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Methanol Mitigation during Manufacturing of Fruit Spirits with Special Consideration of Novel Coffee Cherry Spirits


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Methanol is a natural ingredient with major occurrence in fruit spirits, such as apple, pear, plum or cherry spirits, but also in spirits made from coffee pulp. The compound is formed during fermentation and the following mash storage by enzymatic hydrolysis of naturally present pectins. Methanol is toxic above certain threshold levels and legal limits have been set in most jurisdictions. Therefore, the methanol content needs to be mitigated and its level must be controlled. This article will review the several factors that influence the methanol content including the pH value of the mash, the addition of various yeast and enzyme preparations, fermentation temperature, mash storage, and most importantly the raw material quality and hygiene. From all these mitigation possibilities, lowering the pH value and the use of cultured yeasts when mashing fruit substances is already common as best practice today. Also a controlled yeast fermentation at acidic pH facilitates not only reduced methanol formation, but ultimately also leads to quality benefits of the distillate. Special care has to be observed in the case of spirits made from coffee by-products which are prone to spoilage with very high methanol contents reported in past studies.
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Methanol Mitigation during Manufacturing of Fruit Spirits
with Special Consideration of Novel Coffee Cherry Spirits
Patrik Blumenthal 1,2, Marc C. Steger 1, Daniel Einfalt 2, Jörg Rieke-Zapp 1, Andrès Quintanilla Bellucci 3,
Katharina Sommerfeld 4, Steffen Schwarz 1and Dirk W. Lachenmeier 4,*
Citation: Blumenthal, P.; Steger,
M.C.; Einfalt, D.; Rieke-Zapp, J.;
Quintanilla Bellucci, A.; Sommerfeld,
K.; Schwarz, S.; Lachenmeier, D.W.
Methanol Mitigation during
Manufacturing of Fruit Spirits with
Special Consideration of Novel
Coffee Cherry Spirits. Molecules 2021,
26, 2585.
Academic Editor: Claudio Ferrante
Received: 29 March 2021
Accepted: 23 April 2021
Published: 28 April 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
1Coffee Consulate, Hans-Thoma-Strasse 20, 68163 Mannheim, Germany; (P.B.); (M.C.S.); (J.R.-Z.); (S.S.)
2Yeast Genetics and Fermentation Technology, Institute of Food Science and Biotechnology, University of
Hohenheim, Garbenstrasse 23, 70599 Stuttgart, Germany;
3Finca La Buena Esperanza, Pasaje Senda Florida Norte 124, San Salvador, El Salvador;
4Chemisches und Veterinäruntersuchungsamt (CVUA) Karlsruhe, Weissenburger Strasse 3,
76187 Karlsruhe, Germany;
*Correspondence:; Tel.: +49-721-926-5434
Methanol is a natural ingredient with major occurrence in fruit spirits, such as apple, pear,
plum or cherry spirits, but also in spirits made from coffee pulp. The compound is formed during
fermentation and the following mash storage by enzymatic hydrolysis of naturally present pectins.
Methanol is toxic above certain threshold levels and legal limits have been set in most jurisdictions.
Therefore, the methanol content needs to be mitigated and its level must be controlled. This article
will review the several factors that influence the methanol content including the pH value of the mash,
the addition of various yeast and enzyme preparations, fermentation temperature, mash storage,
and most importantly the raw material quality and hygiene. From all these mitigation possibilities,
lowering the pH value and the use of cultured yeasts when mashing fruit substances is already
common as best practice today. Also a controlled yeast fermentation at acidic pH facilitates not only
reduced methanol formation, but ultimately also leads to quality benefits of the distillate. Special care
has to be observed in the case of spirits made from coffee by-products which are prone to spoilage
with very high methanol contents reported in past studies.
Keywords: alcoholic beverages; spirits; methanol; risk mitigation; legal limits; quality control
1. Introduction
Methanol is an alcohol that is typically found in almost all kinds of alcoholic beverages
and some other fermented food products [
]. Methanol may occur in alcoholic beverages
through two major pathways: a natural one (pectin degradation), as well as an artificial
one (adulteration by illegal addition of the pure compound). Only the latter pathway
(adulteration) is typically associated with major morbidity and mortality due to methanol
poisoning [
]. While adulteration is still prevalent and incidences have increased due to
alcohol shortages during the COVID-19 pandemic [
], this article will exclusively focus on
the first pathway, the natural content of methanol in spirits and its mitigation. Regarding
the mitigation of problems related to methanol addition, we have recently provided a
separate review [11].
In the human body, methanol may be endogenously present in low concentrations [
while in most alcoholic beverages such as beer and wine, the natural content of methanol is also
quite low. This differs with fruit spirits, so that the major focus on methanol reduction measures
lies on this kind of beverage.
Spirits are alcoholic beverages that use fruits or other sugar-containing plant parts as
the raw material. They are produced by alcoholic fermentation followed by distillation [
Molecules 2021,26, 2585.
Molecules 2021,26, 2585 2 of 16
In Central European countries and in Russia, but also in Asia and many American countries,
home production or artisanal small-scale production of spirits has a long tradition, while
typically the sugar-containing materials of the region are preferred. For instance, countries
in Central Europe mainly utilize fruits such as cherries, apples, and plums while other
regions focus on grains (Eastern Europe) or sugar cane materials (Central and Southern
America). From all natural materials used for fermentation, fruits are associated with
the highest concentrations of methanol in the end-product, because of their pectin con-
tent. Typically, stone fruits of the genus Prunus (cherries, plums) and pome fruits of the
genera Malus and Pyrus (apples, pears) are associated with the highest methanol levels.
More recently, coffee cherries (genus Coffea) were identified as fruits possibly leading to
comparably high methanol levels in their spirits [15].
Methanol concentrations in spirits are closely linked to enzymatic activities in the
fruits and during the alcoholic fermentation process. Pectin methylesterase activity (1) may
derive endogenously from the fruits themselves but also during alcoholic fermentation by
pectin methylesterase formed from yeast metabolism or from other microorganisms [
Pectin methylesterase activity may also be exogenously introduced by addition of certain
pectolytic enzyme preparations. A negligible pathway may be thermic demethylation of
pectins [19].
Pectin +H2OPectin methylesterase
Pectic acid +methanol (1)
When methanol has been released from the fruits’ pectin, it inevitably becomes part
of the mash [
]. Its level is dependent on the degree of esterification of the pectin inside
the fruits and the fruit-dependent ratio between sugar and pectin [
]. Another pathway
suggested for methanol formation in protein-rich fruits such as jejube (Chinese date,
Ziziphus jujube Mill.) was glycine deamination, followed by decarboxylation and reaction
with nitrite from fertilizer use [22].
The European Union (EU) regulates maximum methanol contents in spirits depen-
dent on the utilized raw materials [
]. For ethyl alcohol of agricultural origin, the
maximum level of methanol is 30 g/hL of 100% vol alcohol (pure alcohol, pa), while for
vodka it is 10 g/hL pa and the lowest level is defined for London gin with 5 g/hL pa. The
limits are higher for fruit-based materials: for wine spirit 200 g/hL pa, for grape marc and
cider 1000 g/hL pa, for fruit marc 1500 g/hL pa, for fruit spirits in general 1000 g/hL pa,
except 1200 g/hL pa for apples, apricots, plum, mirabelle, peach, pear, blackberry and
raspberry, and 1350 g/hL pa for quince, Williams pear and some other berries [
]. While
these EU limits are set to reduce toxic effects on the human body, they were also judged as
being rather low and, for some types of fruit, as challenging to be upheld by small artisanal
distillers [
]. Lower limits in other countries such as the USA may also prohibit export of
fruit spirits to these countries [26].
This article will review the possibilities to control and reduce the methanol content in fruit
spirts and also describe some initial observations for the novel spirit made from coffee cherries.
2. Materials and Methods
A database research in January 2021 was conducted in Google Scholar and PubMed
using the keyword combination “methanol, “reduction” and “spirits” or “alcoholic bev-
erages”. It became quickly evident that the indexed international literature contains only
few references about the topic. For that reason, the paper collection of the authors was
screened for the key words to identify the gray literature mostly in German language
industry magazines. The reference lists of all identified articles were screened for missing
references. A narrative review was compiled from the available evidence.
3. Toxicity of Methanol in Alcoholic Beverages
Methanol is a colorless liquid and it is highly flammable. It is the simplest alcohol with
a wide range of industrial applications. Methanol is also a natural ingredient in alcoholic
Molecules 2021,26, 2585 3 of 16
beverages and spirits. To ensure that the residual methanol content present in spirits is
safe, methanol content has to be strictly monitored [2,27].
Methanol is one of the few compounds occurring in foods for which excellent human
toxicity data is available. This data mostly origins from the experience with poisonings
from methanol containing spirits that sadly still regularly occur worldwide in connection
with unrecorded and illicit alcohol consumption [
]. Methanol is metabolized in the body
to its toxic metabolites, formaldehyde and formic acid. The accumulation of formic acid
may cause metabolic acidosis including damage to the retina, the central nervous system
and other organs [2,28].
It must be directly noted that such poisonings typically occur from methanol addition
to spirits (mostly found on the illicit market), while the natural content due to fermentation
from fruits does not typically exceed levels causing acute toxicity [11].
Poisoning outbreaks were reported from all regions worldwide, the size of which
ranging from a few to over 800 victims, with fatality rates of over 30% in some instances [
Paine and Dayan [
] reported that the low concentrations of methanol naturally occurring
in most alcoholic beverages are not causing any harm. According to WHO [
], methanol
concentration in typical ranges of 6–27 mg/L in beer and 10–220 mg/L in spirits are not harmful.
Paine and Dayan [
] also reported that the daily tolerable, virtually safe dose of methanol
for an adult is 2 g and the toxic dose is 8 g. For a drinking volume of 100 mL of a spirit at
40% vol
, the tolerable concentration would be 2% vol methanol (i.e., 5000 g/hL pa). Hence, the
EU general limit for naturally occurring methanol in fruit spirits of 1000 g/hL pa [
] offers
a safety margin of about 5 for heavy consumers of fruit spirits. Compared to other toxic food
constituents, this margin is rather low, so that the limits must be strictly controlled and adhered
by industry. Considering the demand for precautionary public health protection, it is obviously
prudent to lower the methanol content in fruit spirits as low as it is reasonably achievable
(ALARA principle).
4. Factors Influencing the Methanol Content of Fruit Spirits
Table 1provides an overview of the major methods and approaches to reduce methanol
in spirits. From their experience in practical work in spirits drinks control and distillation
technology, the authors also provide a judgement about the applicability of the approaches,
considering practical as well as economical aspects. The following sections are considering
each approach in more detail.
Table 1. Summary of major methods to reduce methanol during production of fruit spirits.
Method Methanol Reduction
Potential 1
Authors’ Judgment about
Applicability References
Improvement of quality of
raw material up to 40%
Raw material is extremely important
and the type and quality highly affects
the methanol content. Removal of
pectin-rich fruit parts such as skins may
reduce methanol content.
Acidification of mash up to 50%
Acidification of mash inhibits the
activity of pectin methylesterase. It also
inhibits spoilage microorganisms,
which may produce pectin
Sterilization of mash 40–90%
Temperature treatment efficiently
denaturizes pectin methylesterase
enzymes. High energy requirement and
not feasible for artisanal distillers.
Decreased storage time of
fermented mash before
up to 50%
Storage time should be avoided or
being minimized as far as possible,
because sharp methanol increases were
reported during storage.
Molecules 2021,26, 2585 4 of 16
Table 1. Cont.
Method Methanol Reduction
Potential 1
Authors’ Judgment about
Applicability References
Selection of appropriate yeast
strains up to 25% Yeasts with low capacity of producing
pectin methylesterase to be preferred. [4,30,42,43]
Decreased fermentation
temperature up to 25%
Lower temperatures and the use of cold
fermentation yeast is recommended. [26]
Improvement in distillation
method and conditions up to 80%
Methanol is enriched in tailings. Earlier
cut (not below 50% vol). No recycling
of tailings.
Demethanolization following
distillation 50–90%
Effective in industry but not feasible for
small artisanal distillers, high
Avoidance of liquefaction
enzymes up to 20% Avoid pectin methylesterase enzymes
which release methanol. [4,22,26,34,39,42,47]
Application of alternative
liquefaction enzymes up to 88%
Substitute pectin methylesterase
enzymes by pectin lyase enzymes to
reduce the release of methanol
1Authors’ estimation if several studies were available.
4.1. Raw Materials, Mash Preparation and Fermentation
Prior to sensitization of industry regarding the methanol problem and the implemen-
tation of maximum limits by the EU in the first spirits regulation in 1989 [
], so-called
liquefaction enzymes were often applied during mash preparation. In addition to the de-
sired pectin hydrolysis activity, these enzymes also had pectin esterase activity, resulting in
methanol formation of up to five to six times higher than in untreated fruit mash [
Such conventional, unspecific enzymes should only be used with caution—if at all—and
only if methanol monitoring is implemented [
]. The use of commercial mash enzymes
(i.e., pectolytic enzymes such as pectin methylesterase) always resulted in very high
methanol contents (similar to the maximum methanol release potential) [
]. In the
case of Rubinette apples, methanol increases between 5.5% and 12% occur after addition
of various pectin enzymes, which are used to liquefy the mashes without adding water,
compared to the untreated sample [
]. In quince, the lowest methanol contents were
measured in the mashes blended with 33% water [
]. The avoidance of conventional
liquefaction enzymes alone can lead to a 20% reduction in methanol content [
]. However,
thick fruit mashes usually require a more or less high addition of water for fermentation
and distillation, which means time and increased energy input during distillation, and at
the same time leads to lower alcohol yields [
]. If pectinolytic enzymes have to be applied,
pure lyases should be preferred (see Section 4.1.4). Besides the scrutiny in use of enzymes
the raw material quality, mash preparation and fermentation conditions have potential to
mitigate the methanol release.
4.1.1. Quality and Treatment of Raw Materials
The methanol content is directly related to the fruit type or types used in the fermen-
tation process (mainly dependent on the sugar/pectin ratio) but there are also differences
between cultivars and harvest years [
]. For example, in studying distillates
of Bartlett pear between 1978 and 1995, the 1993 vintage was the year with a strikingly
lower methanol content [
]. In addition to the fruit type, it is very evident that the fruit
quality used affects the quantity of the methanol formation [
]. At what stage of fruit
development and how it is harvested also effects the methanol content [30].
Early harvest or hard pears led to higher methanol levels [
]. For pears and apricots,
other researchers corroborated this finding showing that overripe fruit led to the lowest
Molecules 2021,26, 2585 5 of 16
methanol contents [
]. In deviation of this finding, Adam reported an increase of methanol
through advancing maturity of Williams Christ pears [44,47].
Utilization of plum juice leads to lower methanol contents than plum mashes [
]. On
the other hand, destoned cherry mashes showed higher methanol contents than mashes
with complete fruits including stones [
]. However, in another investigation of the same
research group, destoned cherry mashes showed consistently lower methanol contents [
The conflicting results currently cannot be explained, other than confounding factors not
controlled in the studies.
As pectins have a major occurrence in the skin layer, the removal of the fruit skins
before fermentation may also reduce the methanol level by about 50% during production of
wine spirits [
]. Cores and stems were also described to contain high levels of pectins [
Peeling and coring of pears, therefore, led to a methanol reduction of up to 42% [
However, this method is judged as not economically feasible for most spirits.
4.1.2. Inhibition of Pectin Methylesterase by Acidification of Mash
pH is one of the most important factors which highly affects the activity of enzymes.
Pectin methylesterase showed an optimum at pH 8 and 50
C [
]. Other authors suggested
pH 5–6 as optimum for pectin methylesterase [
]. Pectin methylesterases from yeast
may have optimal pH values ranging from 3.75 to 6 [58].
Therefore, the proposed pH for fermentations to avoid pectin methylesterase activity
is 2.5 [
] (Figure 1). No large differences were reported between pH 2.8 and 3.3,
however [
]. Denes et al. [
] stated a decrease to 1% of the enzyme activity by decreasing
the pH to 4.5 (pectin methylesterase from apples).
Figure 1.
Kinetics of methanol formation in Bartlett pear mashes affected by the initial mash pH and fermentation time
(redrawn from [32]).
There is a clear indication from several studies of an up to 50% reduction in methanol
by acidification of fruit mashes [4,22,25,26,3335].
Molecules 2021,26, 2585 6 of 16
There is not a clear preference about the kind of acid to be used. Gössinger et al.
suggest ortho-phosphoric acid (85%) [
] while Pieper et al. suggested sulfuric acid [
Commercially available products for acidification often contain mixtures of several acids
such as malic acid/hydroxypropionic acid or phosphoric acid/lactic acid.
Gerogiannaki-Christopoulou used citric acid resulting in a decrease of about 15%
methanol in grape pomace distillate [
]. However, while some organic acids such as citric
acid might be depleted during fermentation by their inclusion in metabolic pathways,
inorganic acids appear to be more appropriate. Buffer systems ensuring a long-term
stability of mash pH might be an interesting option for future investigation.
4.1.3. Inhibition of Pectin Methylesterase by Sterilization of Mash
A significant reduction of methanol by 40–90% [
] can be achieved by thermal de-
activation of pectin methylesterase (often referred to as “mash heating”). There are various
suggestions for temperature/time combinations to achieve the enzyme’s denaturation.
Sterilization at temperatures higher than 70
C was generally suggested to effectively
prevent the production of methanol by inactivation of pectin methylesterase [
]. Methanol
can be reduced by targeted thermal deactivation of pectin methylesterase by heating the mash
to 80
C up to 85
C for a holding time of 30 min or to 60
C for 45 min [
]. Pasteurization
at 72
C for 15 s prevented the production of methanol in fermented plant beverages containing
Morinda citrifolia (noni fruit) [
]. In cider spirit, the pasteurization (30 min at 50
C, then
heated to about 85
C) of the apple juice prior to fermentation reduced the methanol content by
34–46% [
]. Lower methanol levels were obtained in Williams and plums by heating the mash
to 65 C for 5 min, followed by re-cooling for fermentation [34].
Xia et al. [
] confirmed that autoclaving by steam injection of the mash of jujube
reduced the methanol content in the spirit significantly by a factor of about eight. The
authors also determined pectin methylesterase activity confirming that their treatment
method reduced the activity to one-fifth to half of that without treatment.
Further technological approaches for inactivation of methylesterase are thermosoni-
cation (ultrasound plus temperature at 70
led to 30% methanol reduction in plum wine)
or use of microwaves (70
C for 1 min led to 70% methanol reduction in plum wine). The
authors indicated an additional nonthermal effect of both ultrasonication and microwaving
with improved sensory properties of the product [41].
4.1.4. Inhibition and Substitution of Pectin Methylesterase by Certain Additives
Pectinolytic enzymes (pectinase) are classified into esterase and depolymerase (lyase
and hydrolase). Lyase produces oligo- or mono-galacturonate, while esterase produces
pectic acid and methanol [
]. The addition of pectin lyase significantly (
= 0.01) reduced
the resulting methanol contents in the mash of apricot and quince by 40–71% [
Lyase appears to inhibit the activity of the naturally contained pectolytic enzymes. The
mechanism was speculated as being a cleavage of the pectin chains by the pectin lyase
in such a fashion that the pectin fragments are not accessible as substrate for the pectin
methylesterase [
]. The effectiveness of lyase enzymes can be increased by dilution of the
mashes with water [
]. Similarly, the addition of certain detergents (anionic surfactants)
as well as polyphenols (tannins) has a reducing effect on the release of methanol by full
or partial inhibition of pectin methylesterases [
]. However, a large amount
of agents is needed, which are rather expensive so that these methods were not widely
implemented in practice [39].
Substituting the application of liquefying pectin methylesterase enzymes by pectinlysase
reduced the methanol concentrations in apple distillates by 40–88%. The combination
of mash sterilization (Section 4.1.3) and pectinlyase liquefaction resulted in an average
methanol reduction of 94 ±4% in the same distillates [48].
Molecules 2021,26, 2585 7 of 16
4.1.5. Selection of Yeast Strains and Fermentation
Microbiological control of the process could also be used to prevent methanol forma-
tion in fermented beverages. For instance, pure culture inoculation using commercial yeast
in contrast to spontaneous inoculation by wild yeasts should be practiced [
]. Mashes
fermented without pure yeast cultures generally lead to higher methanol levels [
]. Yeast
culture selection can reduce methanol contents in the distillates by up to 20% [34].
However, the reason why there are significant differences from yeast breed to yeast breed is
hypothetically due to the fact that the individual breeds apparently differ in their ability to inhibit
pectin esterase and thus the release of methanol from pectin [
]. Strains of Saccharomyces yeasts
may produce all three types of pectinolytic enzymes (see Section 4.1.4) [
]. Selection of yeasts
which do not form pectin methylesterase was suggested to contribute to reduction of methanol
occurrence [
]. Selected mutant Saccharomyces cerevisiae S12 exhibited a methanol content
during wine fermentations decreased by 73% compared to that of the wild-type strain [
]. On
the other hand, Rodríguez Madrera et al. reported lower methanol concentrations in apple
pomace spirits fermented with indigenous yeast than with commercial wine yeast [54].
In a comparison of three different yeast types (one newly developed strain with
improved genetic and physiological performances and two commercial distillers’ yeasts),
the new yeast showed higher methanol contents in plum and pear mashes, but not in cherry
mashes [
]. In another investigation with the same yeast types, the new yeast showed
lower methanol contents in plum mashes but higher in cherry mashes [
]. In a third study
with these yeast types, the new yeast showed consistently lower methanol values than the
commercial yeast in cherry spirits [
]. These conflicting results were interpreted by other
influences on methanol content rather than a yeast influence. Similarly, different strains of
yeast were used in fermentations but no significant change in the quality or quantity was
noticed over time [4].
Another microbiological method for the control of methanol in fermented beverages,
might be the use of methylotrophic yeast such as Pichia methanolica [
] and Candida
boidinii [
] which have the capacity of utilizing pectin or the methyl ester moiety of pectin
and methanol, thus preventing the accumulation of methanol in fermented products [
However, the application of these microorganisms for fermentation of spirits has not been
demonstrated so far.
4.1.6. Fermentation Conditions
The activity of the pectin methylesterase enzyme is directly linked with the tempera-
ture [
]. Increasing the temperature of the mash increases the speed of reaction until the
temperature reaches a very high level where the enzyme starts denaturizing (see Section 4.1.3).
Lowering the fermentation temperature from 20
C to 12
C with use of cold fermentation
yeast may result in a 10–24% reduction in methanol release in the mash [
], but not in all
cases [25,26].
4.2. Storage of Fermented Mash before Distillation
Generally, the storage time following fermentation has a major influence on the
methanol release (Figure 1) [
]. Depending on the pH level, an almost 100% release can
be expected after only some weeks of storage. During mash storage of 4 weeks, methanol
contents increased, in some cases sharply by 15–50% [
]. Therefore, the optimal practice
would be to conduct the distillation as soon as fermentation has been complete or at least
to minimize storage time as far as possible [33].
4.3. Distillation Method and Conditions
4.3.1. Methanol Reduction during Pot Still Distillation
Methanol has a boiling point (64.7
C) that is considerably lower than the ones of
ethanol (78.5
C) and water (100
C). However, it is nevertheless difficult to separate
methanol from the azeotropic ethanol-water mixture [
]. When the alcohol mixture is
distilled in simple pot stills such as the ones used by most small-scale artisanal distilleries
Molecules 2021,26, 2585 8 of 16
throughout Central Europe, the solubility of methanol in water is the major factor rather
than its boiling point. As methanol is highly soluble in water, it will distil over more at the
end of distillations when vapours are richer in water. That means, methanol will appear
in almost equal concentration in almost all fractions of pot still distillation in reference to
ethanol (i.e., as g/hL pa), until the very end where it accumulates in the so-called tailings
fraction (Figure 2) [
]. However, even today many professional distillers
believe that methanol concentrates preferably in the first fractions (heads fractions). And
that methanol is the reason that heads fractions smell and taste bad (which is caused
by acetaldehyde and ethyl acetate but not by methanol). It is of note that single studies
that suggested that methanol may be enriched in the first distillation fractions were not
plausible and potentially erroneous (e.g., compare the abstract with the conclusion section
in Xia et al. [
], which report completely conflicting information—from the data presented
in the work it can be assumed that the study from China is in fact corroborating the studies
from Europe and the United States that methanol is enriched in the tailings while the
information in the abstract that it is enriched in the heads fractions is most probably a
translation mistake).
Figure 2.
Distillation characteristics of ethanol and methanol affected by different reflux ratios (v) during distillation of
Bartlett pear mashes (redrawn from [32]).
Various distillation tests carried out show that the methanol content in the product
(hearts) fractions can hardly be influenced by different distillation techniques. Even in
experiments with various “catalysts”, no groundbreaking findings have yet emerged. Only
relatively expensive silver wool as adsorbent led to methanol reductions of up to 20% [
Therefore, the separation of tailings, which also has to be done for sensorial reasons,
is so far the only option for a reduction of methanol during pot still distillation. The
reduction of methanol contents of the product fractions in g/hL pa compared to mash may
be between 20 and 30%. On the other hand, an extremely late separation of tailings can
cause an increase of methanol contents of about 20% in the product fractions [39].
In general, it can be seen that the methanol content in the spirit increases with reflux
ratio increases. That means the higher the reinforcement and the slower the distillation is,
the higher the methanol content in the distillate [
] (Figure 2). Distillation parameters
also had an influence on the methanol content of the distillates. Especially the dephlegmator
Molecules 2021,26, 2585 9 of 16
temperature showed a significant effect on the methanol content. Within the parameters
tested using 150 L still, three trays and one dephlegmator, the decrease in methanol content
varied between 16% and 36% [25].
On the other hand, Scherübel [
] suggests the following three measures to reduce
methanol by improvements in pot still distillation:
Perform double distillation: it is always advisable to carry out two subsequent distilla-
tions with regard to methanol separation
Increase separation efficiency: The methanol separation can be increased by a simple
optional parallel connection of a conventional spirits tube and a more separation-
efficient column. If possible, this column should be at least partially cooled at the top
to increase internal reflux and thus separation efficiency.
Cooling at the head: When use of an additional column is not feasible, partial cooling
of the spirits tube at the beginning of the second distillation can also increase the
internal reflux and thus increase the separation efficiency.
In summary, there is still a bit of discrepancy regarding the influence of reflux ratios
between the different studies in the literature. This can probably be explained by the wide
variability of commercially available stills and legal differences (number of plates) for
artisanal distilleries in different jurisdictions.
4.3.2. Methanol Reduction during Large-Scale Distillation
In contrast to pot stills that typically consist of a small column (three or four plates),
industrial-scale distilleries with 15 to 30 plates provide the possibility of continuous distil-
lation and advanced regulation of distillation including processes of demethylation [39].
Methanol content can be decreased during the rectification by using demethanolization
columns [
]. This process is efficient and successfully reduces the methanol content up
to 40–90% in comparison to the starting amount. However, investment is only viable for
rather big businesses with high capacity utilization [39].
A combined evaporation/condensation method to reduce methanol from distillates was
patented by Capovilla [
]. The application of the method was found to reduce methanol
in fruit spirits by 58–190 g/hL pa [
]. However, such methods may not be economically
viable as they considerably reduce the alcohol content along with the methanol content [
The promised results of the evaporation/condensation method were also criticized as im-
plausible with independent investigations showing lesser methanol reduction (9–92 g/hL pa)
always connected with inacceptable losses of ethanol (up to 10% vol) [
]. All in all evapo-
ration/condensation methods for demethanolization were judged as economically unviable
specifically for smaller businesses.
4.4. Storage of Distillate after Fermentation
Not much evidence is available regarding the methanol evolution during the distillates’
storage and aging process. Botelho et al. [
] suggested a tendency for low amounts of
methanol in advanced wood-cask aged spirits, attributable to methanol oxidation and
subsequent acetalization reaction with the formation of diethoxymethane. On the other
hand, methanol is expected to be quite stable in inert containers without the presence
of oxygen. This is also in line with the authors’ experience from validating methods for
methanol determination, which suggested that methanol is a stable compound in bottled
hydroalcoholic solutions [67].
Similar results were observed by Xia et al. [
]. The 270-day storage of jujube spirit
in oak barrels significantly reduced its methanol content, while lower reductions were
observed in plastic or stainless-steel containers. The authors explained the reduction by
esterification reactions but were unable to provide explanation for the differences between
container materials.
Molecules 2021,26, 2585 10 of 16
5. Discussion
5.1. Good Manufacturing Practice for Methanol Reduction Leading to Decreased Levels in
Commercial Products
The only currently available review about methanol reduction possibilities has been
provided by Botelho et al. [
] in the context of a more general review on quality of fruit
spirits. While being less comprehensive and lacking the coverage of major studies only
available in German language, the major areas influencing the methanol content in fruit
spirits were in agreement with this review, namely, raw material quality, fermentation,
storage, and distillation. Botelho et al. [
] concluded that the reduction of the time between
fermentation and distillation being the most effective way to reduce the methanol content
of the final beverage, with that suggestion to be classified as “good manufacturing practice”.
This is also in agreement with the comprehensive book of Adam and Versini published by
the European Commission [39].
The quality of the raw material used is a key factor which defines the quality of the
spirit produced and its methanol content. Alcoholic beverages derived from materials low
in pectin content (such as beer, wine or grain-based spirits such as whiskey) have typically
a much lower concentration of methanol than fruit-based products. Mitigation efforts in
the past were therefore focused on fruit spirits.
Previous results have shown that industry efforts and application of improved fermen-
tation and distillation technology have led to lowered methanol levels in fruit spirits [
Due to the limits for methanol introduced uniformly throughout Europe in 1989, processes
were developed to reduce this substance in spirits [
]. Methanol release during fermenta-
tion and distillation is not a univariate process, but a combination of several measures can
effectively ensure methanol levels below legal limits.
According to Glatthar et al. [
], the following mitigation measures are simple and
can be applied even by small, artisanal distilleries:
Adjust the mash pH before fermentation to pH 2.5–3.0
Short fermentation using inoculation with yeasts followed by immediate distillation
Do not recycle the tailings
Using these measures, a methanol content reduced by half, without changing the
sensory quality of the products, can be expected.
Interestingly, all the measures discussed before may have led to considerably decreased
levels of methanol in commercial products on the European market and can be seen as an
excellent example of implementation of research results into practice. This may be evidenced
by the efforts of the researchers to publish their results in addition to the usual peer-reviewed
journals in trade journals in a format readable and understandable by distillers.
Adam and Postel [
] showed that cherry brandies tested in 1991 had almost 100 g/hL pa
less methanol than cherry brandies produced before 1986. Adam and Versini [
] confirmed
this trend in 1996. Own investigations of 923 cherry spirits (Figure 3), which is one of the
most frequently tested product groups at the CVUA Karlsruhe as this product is traditionally
a specialty of North Baden or the Black Forest, analyzed during the years 1980–2020 confirm
a statistically significant linear decrease in methanol content (r =
0.345, p< 0.0001). Mean
methanol contents decreased from an average of 500 g/hL pa in the early 1980s to an average
of 400 g/hL pa at present (for methodology and details on samples 1980–2003, see [
]). None of
the samples was found to exceed the EU limit of 1000 g/hL pa.
Molecules 2021,26, 2585 11 of 16
Figure 3. Methanol contents of 923 cherry spirits analysed between 1980 and 2020.
5.2. Coffee Spirits—A Special Case for Methanol Mitigation
Despite some anecdotal evidence that spirits derived from coffee cherries or coffee
by-products were traditionally manufactured in some coffee-producing countries such
as Nepal, there is not only extremely limited evidence on production methods [
] but
also on chemical composition and specifically the methanol content of coffee cherry spirits.
Especially the coffee pulp juice from wet-processing with about 3–5% of total sugars is
an adequate substrate for production of ethanol [
]. For coffee mucilage from various
Coffea arabica varieties, the pectin yield in the coffee fruit was 0.03–0.09% and methoxyl
esterification degrees of 19–31% were reported [
]. Coffee pulp of Coffea canephora contains
2–3% pectin with a methoxyl esterification degree of about 6% [
], while higher contents
were reported for Coffea arabica with 15% pectin in dried pulp with a methoxyl esterification
degree of 63% [
]. Another study reported 11% pectin in Coffea arabica without specifying
the esterification degree [74].
Depending on species and processing, the pectin content of Coffea by-products could be
higher than the one in most other fruits used for spirits production, such as cherries (0.4%),
apricots (1%), or apples (0.8%) [
], while the methoxyl degree of Prunus avium cherries
was between 44% and 91% depending on extraction method and ripening stage [
]. Hence,
the capacity for enzymatic methanol formation may be higher in coffee cherries than in
conventional materials for fruit distillate production. From the few studies on spirits
produced from coffee cherries or coffee-by products many did not investigate methanol
contents [
], which is a bit puzzling because methanol is typically included in any
standard spirits analysis [82].
Nevertheless, there are some studies on methanol in fermentations of coffee materials
available (Table 2). Bonilla-Hermosa et al. [
] showed comparably low levels of methanol
in coffee pulp mixed with coffee wastewater from the depulping and demucilage process
of Coffea arabica beans. However, only the fermentation mash was analyzed in this case
and no distillation was conducted. A study of spent coffee grounds fermented with
Molecules 2021,26, 2585 12 of 16
added sugar of 180 g/L also showed rather low levels of methanol. On the other hand,
Somashekar and Appaiah [
] showed that solid substrate fermentation of coffee cherry
husk from Coffea canephora with Clavispora and Pichia strains may lead to considerable levels
of 7.2–10.8% methanol. The process was intended for technical alcohol production and
appears as completely unsuitable for obtaining products for human consumption. While
the production of technical alcohols from coffee by-products and waste-products could be
an interesting valorization option, this study shows that extreme scrutiny has to be applied
if spirits from coffee by-products are intended to be used as consumer products.
This concern was strengthened by the informative pilot study of Einfalt et al. [
reporting results of coffee cherry spirit production. The mash was prepared using Coffea
arabica cherries transported in frozen form from Thailand to Germany, where they were
pulped. After lowering the pH to 3.1 using phosphoric acid/lactic acid addition, a com-
mercial pectinase enzyme was added for liquefaction. After addition of commercial yeast,
the mash was distilled after 17 days of fermentation. The methanol content in the hearts
fractions was 2600
400 g/hL pa, which considerably exceeded the EU limit of 1000 g/hL
pa and offers a safety margin of less than 2 for the level of acute toxicity of 5000 g/hL pa
(see Section 3). The authors suggested that the application of pectinase and the long storage
had an adverse effect on the methanol concentration [
], which is plausible considering
our review results in Sections 4.1 and 4.2.
In a patented method by Bodmer and Ruder [
], whole coffee cherries were mashed
with addition of 5% sugar, adjusted to pH 3.0 with phosphoric acid/lactic acid, and pitched
with Saccharomyces cerevisiae yeast and diammonium phosphate. After a fermentation
time of 7–14 days, the mash was double-distilled using pot still technique. The methanol
contents of two coffee cherry spirits were 684 and 573 g/hL pa. While the production
method with addition of sugar is not compliant with the EU regulation for fruit spirits,
where the products’ ethanol must exclusively originate from fruits [
], this also lowers
the relative methanol content by increasing the ethanol content. Hence, it can be deduced
from the results that a coffee cherry spirit production according to the patented method,
excluding artificial sugar addition, would lead to a methanol limit exceedance similar to
the results of Einfalt et al. [15].
In conclusion, apart from the lack of novel food approval [
], none of the coffee cherry
spirits presented so far would have been compliant with the EU spirits regulation. It is
clearly necessary to apply the gathered knowledge about methanol mitigation possibilities
in further research of this interesting novel type of spirit, so that compliant coffee cherry
spirits will hopefully be available in the future.
Table 2. Methanol content in spirits produced from coffee cherries and coffee by-products.
Raw Material Methanol Content Compliance with EU
Regulation for Fruit Spirits 1References
Coffee cherry 2600 ±400 g/hL pa no 2[15]
Coffee cherry + 5% sugar 573–684 g/hL pa no 3[84]
Coffee cherry husk 7–11% (non-food product) [83]
Coffee pulp mixed with coffee
wastewater (1:10) 40–128 µg/L (in mash) (no distillation conducted) 4[74]
Spent coffee grounds + 18% sugar
11 ±3 mg/L
(44 ±12 g/hL pa 5)no 4[86]
This does not suggest general compliance with EU food regulations. Novel food approval is needed in the EU for most coffee by-products
and derivative products before being placed on the market [
Exceedance of general methanol limit for fruit spirits of 1000 g/hL pa [
The production method with added sugar is not compliant with EU regulations for fruit spirits; without sugar addition, the methanol
limit of 1000 g/hL pa would have likely been exceeded.
Fruit sprit ethanol must exclusively originate from fresh fruits [
] and not from
waste products such as spent coffee grounds or wastewater. Potential compliance in another spirit drinks’ category or as a generic ‘spirit
drink’ needs to be checked. 5Recalculation (alcoholic strength at 40% vol).
Molecules 2021,26, 2585 13 of 16
6. Conclusions
The methanol content is among the key parameters for determining the regulatory
compliance of spirits and other alcoholic beverages. The mitigation measures developed
over the last decades allowed industry not only to conform to the EU standards but also to
increase the margin of safety by generally lowering the methanol content in the category of
fruit spirits.
Interestingly, coffee cherry pulp, which is produced in large quantities as a by-product
of coffee manufacturing, was proposed as a material to produce spirits. Very high con-
centrations of methanol were found in coffee cherry spirit compared to other fruit spirits.
Hence it is specifically necessary to mitigate the methanol content in these spirits to uphold
the legal requirements and to protect public health from this potential hazard.
Author Contributions:
Conceptualization, D.W.L.; methodology, D.W.L.; formal analysis, D.W.L.
and K.S.; investigation, P.B. and M.C.S.; resources, D.W.L.; data curation, D.W.L.; writing—original
draft preparation, D.W.L.; writing—review and editing, P.B., M.C.S., D.E., J.R.-Z., A.Q.B., K.S., S.S.;
visualization, D.W.L.; supervision, D.W.L. and S.S.; project administration, D.W.L. and S.S. All authors
have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Acknowledgments: Aliazam7786/Fiverr is thanked for redrawing Figures 1and 2.
Conflicts of Interest:
S.S. is owner of and P.B., M.C.S. and J.R.Z. are consultants for Coffee Consulate,
Mannheim, Germany. Coffee Consulate is an independent training and research center. A.Q.B. is
owner of Finca La Buena Esperanza, a coffee plantation in El Salvador. Coffee Consulate and Finca
La Buena Esperanza are currently researching the potential of coffee by-products for production of
spirits. Neither of them are currently commercializing spirits produced from coffee by-products.
Therefore, S.S., P.B., M.C.S., J.R.-Z., and A.Q.B. report no conflict of interest related to the work under
consideration. The other authors declare no conflict of interest.
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... The enzyme pectin methylesterase transforms pectin into pectic acid and methanol [36]. As fruits contain high amounts of pectin, spirits made from them (such as plums, apples or coffee cherries) also have a higher methanol content compared to distillates made from grains or sugar cane [21]. Both mashes, YC and YI, showed an almost similar methanol concentration, whereas the value of BT was lower. ...
... The results of these experiments show that the methanol content could almost be reduced by half compared to a previously produced coffee cherry spirit with a methanol content of 2600 ± 400 g/hL pa [18]. The use of a very fresh substrate, the short fermentation period and the direct distillation after the end of fermentation may have contributed to the lower methanol content [21]. However, it must also be noted that the raw material cannot be exactly compared with each other. ...
... In the tail fractions of the three samples, a higher methanol concentration was detected than in the heart fractions. This behavior is similar to the distillate analysis with GC-FID of Einfalt et al. [18] and literature data on other fruit spirits [21]. Methanol has a lower boiling point than ethanol and should therefore evaporate earlier. ...
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Coffee pulp, obtained from wet coffee processing, is the major by-product accumulating in the coffee producing countries. One of the many approaches valorising this underestimated agricultural residue is the production of distillates. This research project deals with the production of spirits from coffee pulp using three different Coffea arabica varieties as a substrate. Coffee pulp was fermented for 72 hours with a selected yeast strain (Saccharomyces cerevisiae L.), acid, pectin lyase, and water. Several parameters, such as temperature, pH, sugar concentration and alcoholic strength were measured to monitor the fermentation process. Subsequently, the alcoholic mashes were double distilled with stainless steel pot stills and a sensory evaluation of the products was conducted. Furthermore, the chemical composition of fermented mashes and produced distillates were evaluated. It showed that elevated methanol concentrations were present in mashes and products of all three varieties. The sensory evaluation found the major aroma descriptor for the coffee pulp spirits as being stone fruit. The fermentation and distillation experiments revealed that coffee pulp can be successfully used as a raw material for the production of fruit spirits. However, the spirit quality and its flavour characteristics can be improved with optimised process parameters and distillation equipment.
... The enzyme pectin methylesterase transforms pectin into pectic acid and methanol [36]. As fruits contain high amounts of pectin, spirits made from them (such as plums, apples or coffee cherries) also have a higher methanol content compared to distillates made from grains or sugar cane [21]. Both mashes, YC and YI, showed an almost similar methanol concentration, whereas the value of BT was lower. ...
... The results of these experiments show that the methanol content could almost be reduced by half compared to a previously produced coffee cherry spirit with a methanol content of 2600 ± 400 g/hL pa [18]. The use of a very fresh substrate, the short fermentation period and the direct distillation after the end of fermentation may have contributed to the lower methanol content [21]. However, it must also be noted that the raw material cannot be exactly compared with each other. ...
... A higher methanol concentration was detected in the tail fractions of the three samples than in the heart fractions. This behavior is similar to the distillate analysis with GC-FID by Einfalt et al. [18] and literature data on other fruit spirits [21]. Methanol has a lower boiling point than ethanol and should therefore evaporate faster. ...
Full-text available
Coffee pulp, obtained from wet coffee processing, is the major by-product accumulating in the coffee producing countries. One of the many approaches valorising this underestimated agricultural residue is the production of distillates. This research project deals with the production of spirits from coffee pulp using three different Coffea arabica varieties as a substrate. Coffee pulp was fermented for 72 h with a selected yeast strain (Saccharomyces cerevisiae L.), acid, pectin lyase, and water. Several parameters, such as temperature, pH, sugar concentration and alcoholic strength were measured to monitor the fermentation process. Subsequently, the alcoholic mashes were double distilled with stainless steel pot stills and a sensory evaluation of the products was conducted. Furthermore, the chemical composition of fermented mashes and produced distillates were evaluated. It showed that elevated methanol concentrations (>1.3 g/L) were present in mashes and products of all three varieties. The sensory evaluation found the major aroma descriptor for the coffee pulp spirits as being stone fruit. The fermentation and distillation experiments revealed that coffee pulp can be successfully used as a raw material for the production of fruit spirits. However, the spirit quality and its flavour characteristics can be improved with optimised process parameters and distillation equipment.
... Methanol is a commonly occurring toxic contaminant of alcoholic beverages (Blumenthal et al., 2021;Ohimain, 2016;World Health Organisation, 2014). Because of its similarity to ethanol and lower price, methanol has long been used to fortify informally and illicitly produced alcoholic drinks (Blumenthal et al., 2021;Everstine et al., 2013;Ohimain, 2016;World Health Organisation, 2014). ...
... Methanol is a commonly occurring toxic contaminant of alcoholic beverages (Blumenthal et al., 2021;Ohimain, 2016;World Health Organisation, 2014). Because of its similarity to ethanol and lower price, methanol has long been used to fortify informally and illicitly produced alcoholic drinks (Blumenthal et al., 2021;Everstine et al., 2013;Ohimain, 2016;World Health Organisation, 2014). These adulterated beverages are sold illegally and there are many accounts of methanol poisoning worldwide, with examples in numerous African (Gambia, Kenya, Libya, Nigeria, Sudan, Uganda), American (Costa Rica, Ecuador, Mexico, Nicaragua), Asian (Cambodia, India, Indonesia, Iran, Malaysia, Pakistan, Turkey), and European (Czech Republic, Estonia, Norway, Romania) countries (AbdulRahim and Shiekh, 2012;Adil et al., 2019;Doreen et al., 2020;Hassanian-Moghaddam et al., 2015;Hovda et al., 2005;Lachenmeier et al., 2021;Levy et al., 2003;Ohimain, 2016;Paasma et al., 2007;Pressman et al., 2020;Rostrup et al., 2016;World Health Organisation, 2014Zakharov et al., 2014; for more details on these acute methanol poisonings see Supplementary Table 1). ...
... While the risks of drinking methanol in adulterated beverages are widely recognised, it is rather less well known that methanol is also present naturally in traditional alcoholic beverages produced in different parts of the world (Ohimain, 2016). These are made from fermentation of products grown locally, such as sap of raffia and oil palms, sorghum, millet, maize, rice and banana in Africa and Asia, sugarcane and agave in Central and South America (Ohimain, 2016), and grains and fruits, including wheat, barley, apple, apricot, cherry, grape, mirabelle, peach, pear, and plum in Europe (Blumenthal et al., 2021). Methanol is derived from pectin in the raw materials (Ohimain, 2016). ...
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Methanol is present at high concentrations in unrecorded fruit spirits, placing consumers of these beverages at risk of exposure at high levels. When assessing any health risk it is necessary to consider blood methanol levels (BMLs), reference doses (RfD), and maximum tolerable blood methanol levels (MTBML). The aim of our study was to estimate daily methanol intake and related BMLs attributable to drinking unrecorded fruit spirits in the European population using a probabilistic Monte Carlo simulation. Data on the concentration of methanol in unrecorded fruit spirits in European Union member states were collected and the health risk posed by consumption of unrecorded fruit spirits was estimated. We found that drinking unrecorded fruit spirits containing methanol at a concentration higher than 8598.1 mg/litre of pure alcohol (p.a.) or 6382.1 mg/litre of p.a. and also at least 10 g ethanol can result in a methanol intake above the RfD by men and women, respectively. We confirmed that consumption of unrecorded fruit spirits containing methanol does not result in BMLs higher than the MTBML. Further studies are required to assess whether there is any health risk from chronic exposure to methanol above the RfD from unrecorded fruit spirits.
... Thus, it can be present at high levels in the final spirits. The concentration of methanol in fruit spirits is influenced by many factors: the type and quality of the raw material (polymers of galacturonic acid are located in the cell walls of plant tissues; therefore, methanol concentration is directly correlated with the pectin content of the fermented material), acidification of fruit mash and other conditions of the fermentation process, storage time between fermentation and distillation and, finally, the details of the distillation process [5,7,31]. The mean concentrations (n = 3) of the methanol in plum spirits samples are presented in Table 2 and as it could be seen the concentration of methanol was influenced by plum cultivar used. ...
In Bosnia and Herzegovina plum spirits are often made in small quantity production batches, involving pot still alembic vessels. In many cases the producer will utilize plums still retaining their stone during the fermentation process which results in important contributions to the overall complexity of final spirit aroma. Plum spirits are characterized by an intense fruity aroma. However, these spirits can also contain some harmful compounds. In this study were determined the concentration of the methanol and hydrocyanic acid (HCN) that are toxic and acetaldehyde and furfural that are harmful just if they are present in higher concentration. Plum spirits were obtained using three plum variety: Pozegaca, Stanley and Bilska rana (Buchler). The behavior of these major harmful compounds was followed during distillation, with their respective contents measured in the heads, hearts, and tails fractions. The most abundant compound was methanol, which is concentrated in the heart fraction, reaching a maximum value of 9668 mg·L-1 absolute alcohol, in the heart fraction of Bilska rana spirit. The concentration of HCN and furfural was influenced by the plum cultivar, the spirits made from the Stanley cultivar contained higher concentrations of these two compounds. The concentrations of harmful compounds are seen not to exceed the allowed limit if an adequate fraction of the heart and tail fractions are removed.
... The presence of competing products and organic acids from the FLW and the fermentation broth can create challenges in economic separation of the ethanol. In addition to that, the type of FLW used consisting of pectin can also pose challenges for the downstream processing, as pectin can be converted to methanol during fermentation that can cause the separation challenges [189][190][191]. In the batch processes, the carbon source is usually utilized to exhaustion; however, in the fed-batch processes, the remaining amount of carbon source can interfere in the product separation. ...
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The increasing global population will require sustainable means to sustain life and growth. The continuous depletion and increasing wastage of the energy resources will pose a challenge for the survival of the increasing population in the coming years. The bioconversion of waste generated at different stages of the food value chain to ethanol can provide a sustainable solution to the depleting energy resources and a sustainable way to address the growing food waste issue globally. The high carbohydrate and nitrogen content in the food waste can make it an ideal alternative substrate for developing a decentralized bioprocess. Optimizing the process can address the bottleneck issues viz. substrate collection and transport, pretreatment, fermentative organism, and product separation, which is required to make the process economic. The current review focuses on the opportunities and challenges for using the food loss and waste at different stages of the food value chain, its pretreatment, the fermentation process to produce bioethanol, and potential ways to improve the process economics. The impact of substrate, fermentative organisms' process development , downstream processing, and by-product stream to make the bioethanol production from the waste in the food value chain a commercial success are also discussed.
... Notoriously, acetaldehyde, ethylacetate and methanol are the major markers of wine aging, as acetaldehyde derives from the ethanol oxidation and yeast metabolism during and after alcohol fermentation as well [102]; ethyl acetate is obtained from yeast and acetic bacteria metabolism; while methanol is derived from enzymatic degradation of grape pectins in the fruits and during the alcoholic fermentation [103,104]. Except for methanol, which is not involved in the flavor, aroma and mouth-feel of wine [104], the acetaldehyde may enhance the fruity aroma at a low concentration. However, at higher levels, it is reminiscent of ethereal and ripe apple notes, and above 100 mg/L is then considered as a defect [105]. ...
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Traditional alcoholic beverages have always been part of the Mediterranean culture and, lately, they have been re-evaluated to valorize both the territory and local customs. In this study, the Amarena wine, a fortified wine included in the national list of the traditional agri-food products, was characterized during bottle aging for oenological parameters, chromaticity, volatiles, and inorganic elements. Then, experimental data were visually interpreted by a principal component analysis (PCA). PCA revealed that most of oenological parameters (i.e., alcoholic grade, total dry extract, sugars, organic acids, and phenolic compounds) had a scarce discriminating power. Additionally, ethyl esters were only present in younger products, while remaining at quite constant levels. Conversely, certain metals (i.e., Mg, Na, Mn, Zn, and Cu), chromatic properties, and pH differentiated older Amarena bottles from the younger counterpart. Particularly, acetaldehyde and furanic compounds proved to be valid aging markers. A sensorial analysis highlighted that fruity and floral odors and flavors characterized younger beverages, while dried fruity, nutty, and spicy notes were displayed by older products, along with the valuable attribute of “oxidized” typically observed in aged Sherry wines. Overall, this study may encourage the production and commercialization of the Amarena wine, thus preserving the cultural heritage of the Mediterranean area.
... This compound is found frequently in fruit-based drinks where pectin is hydrolyzed prior to or during fermentation by pectin methyl esterases (PME), which release the methoxy groups generating methanol (Bindler et al., 1988;Pineau et al., 2021). To reduce the production of methanol, processes such as the removal of the peel or skin of fruits (Hodson et al., 2017), use of very ripe fruit, heating and/or pasteurization to deactivate the PME enzyme (Hang and Woodams, 2010;Miljić et al., 2016), chemical pasteurization using dimethyl dicarbonate (Blumenthal et al., 2021) and even PME enzyme inhibitors such as the use of epigallocatechin gallate (EGCG) (Saelee et al., 2020) have been used. ...
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Mezcal is a traditional iconic Mexican distilled beverage obtained from varied species of agaves. Regardless of the area of production, the process always consists of five stages: harvesting the agaves, cooking, crushing, fermentation, and distillation. It is produced in a large area of Mexican territory, a large part of which is protected by the Denomination of Origin mezcal (DOM). Over time, the word mezcal has evolved from a generic name to a more specific term used to describe the agave-distilled beverages produced in the territory protected by the DOM under the Mexican official standard NOM-070-SCFI-2016 which defined Mezcal as a “Mexican distilled alcoholic beverage, 100% from maguey or agave, obtained by distillation of fermented juices with spontaneous or cultivated microorganisms, extracted from mature heads of maguey or cooked agaves, harvested in the territory covered by the DOM.” In the last 10 years, official production has increased, from <1 million liters in 2011 to almost 8 million liters. This substantial increase in production puts a lot of pressure on resources, in particular raw material, as part of the production is obtained from wild agave. On the other hand, it exposes tradition at risk by increasing production by modernizing production processes and sacrificing the artisanal aspect of this production. We consider appropriate to address the issue of sustainability in this context of great tradition and growing market demand. The article presents the relevant aspects of mezcal production, highlighting some particularities specific to certain production areas, it also addresses the problem of the official standard. A broad discussion is presented on the sustainability of artisanal processes, and the main points to be taken care of in this framework. Additionally, some elements considered as fundamental in the perspective of the design of a sustainable artisanal distillery are described. In summary, this article aims to review the current state of mezcal production, how sustainability may be addressed in a very artisanal process and what are the challenges of the production chain to satisfy an increase in demand without sacrificing the tradition and culture related to this iconic Mexican beverage.
... The methanol concentrations indicated a typical behavior for fruit spirit distillation processes [45,51]. They showed slightly higher concentrations during the beginning and the end of the distillation run. ...
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Fruit spirit distillations processes are based on physical principles of heat and mass transfer. These principles are decisive for the separation of desired and undesired aroma compounds, which affect the quality of the distilled product. It is mandatory to control heat and mass transfer parameters to be able to perform fruit spirit distillation processes in a reproducible manner and to achieve equal products with similar volatile compound compositions repeatedly. Up to now, only limited information is available on the magnitude of reproducibility errors since fruit spirit distillation columns are typically not equipped with a suitable control or monitoring technique. We upgraded a batch distillation column with digitized instrumentation and a control technique to be able to control crucial parameters such as thermal energy inputs and reflux rates. This study aimed to identify whether control over two distillation parameters has the potential to enable us to perform distillation processes repeatedly. This study analyzed the magnitude of reproducibility errors for (i) six monitored distillation process parameters and (ii) 13 quantified volatile compounds in the product between duplicated distillation runs performed with equal setups. A total of eight different distillations were performed in duplicate (n = 16), while the six distillation parameters were monitored and logged every ten seconds. The produced distillates were equally subsampled into 20 fractions and each fraction analyzed for 13 volatile compound concentrations. Based on a dataset of 28,600 monitored duplicate distillation process data points, this study showed that process parameters can indeed be replicated with a median relative standard deviation (RSD) of
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The commercial active dry yeast strains used for cider production in China are far behind the requirements of the cider industry development in recent decades. In this study, eight yeasts, including Saccharomyces cerevisiae, Schizosaccharomyces pombe, Pichia bruneiensis, and Pichia kudriavzevii, were screened and assessed by growth performance, methanol production, aroma analysis, and their transcriptive characterization. Saccharomyces cerevisiae strains WFC-SC-071 and WFC-SC-072 were identified as promising alternatives for cider production. Strains WFC-SC-071 and WFC-SC-072 showed an excellent growth capacity characterized by 91.6 and 88.8% sugar utilization, respectively. Methanol production by both strains was below 200 mg/L. Key aroma compounds imparting cider appreciably characteristic aroma increased in cider fermented by strains WFC-SC-071 and WFC-SC-072. RT-qPCR analysis suggested that most genes associated with growth capacity, carbohydrate uptake, and aroma production were upregulated in WFC-SC-071 and WFC-SC-072. Overall, two Saccharomyces cerevisiae strains are the optimal starters for cider production to enable the diversification of cider, satisfy the di erences in consumer demand, and promote cider industry development.
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Ethanol is a promising biofuel that can replace fossil fuel, mitigate greenhouse gas (GHG) emissions, and represent a renewable building block for biochemical production. Ethanol can be produced from various feedstocks. First‐generation ethanol is mainly produced from sugar‐ and starch‐containing feedstocks. For second‐generation ethanol, lignocellulosic biomass is used as a feedstock. Typically, ethanol production contains four major steps, including the conversion of feedstock, fermentation, ethanol recovery, and ethanol storage. Each feedstock requires different procedures for its conversion to fermentable sugar. Lignocellulosic biomass requires extra pretreatment compared to sugar and starch feedstocks to disrupt the structure and improve enzymatic hydrolysis efficiency. Many pretreatment methods are available such as physical, chemical, physicochemical, and biological methods. However, the greatest concern regarding the pretreatment process is inhibitor formation, which might retard enzymatic hydrolysis and fermentation. The main inhibitors are furan derivatives, aromatic compounds, and organic acids. Actions to minimize the effects of inhibitors, detoxification, changing fermentation strategies, and metabolic engineering can subsequently be conducted. In addition to the inhibitors from pretreatment, chemicals used during the pretreatment and fermentation of byproducts may remain in the final product if they are not removed by ethanol distillation and dehydration. Maintaining the quality of ethanol during storage is another concerning issue. Initial impurities of ethanol being stored and its nature, including hygroscopic, high oxygen and carbon dioxide solubility, influence chemical reactions during the storage period and change ethanol’s characteristics (e.g., water content, ethanol content, acidity, pH, and electrical conductivity). During ethanol storage periods, nitrogen blanketing and corrosion inhibitors can be applied to reduce the quality degradation rate, the selection of which depends on several factors, such as cost and storage duration. This review article sheds light on the techniques of control used in ethanol fuel production, and also includes specific guidelines to control ethanol quality during production and the storage period in orderto preserve ethanol production from first‐generation to second‐generation feedstock. Finally, the understanding of impurity/inhibitor formation and controlled strategies is crucial. These need to be considered when driving higher ethanol blending mandates in the short term, utilizing ethanol as a renewable building block for chemicals, or adopting ethanol as a hydrogen carrier for the long‐term future, as has been recommended.
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Spirits are alcoholic beverages commonly consumed in European countries. Their raw materials are diverse and include fruits, cereals, honey, sugar cane, or grape pomace. The main aim of this work is to present and discuss the source, quality control, and legal limits of methanol in spirits produced using fruit and honey spirits. The impact of the raw material, alcoholic fermentation, and the distillation process and aging process on the characteristics and quality of the final distilled beverage are discussed. In addition, a critical view of the legal aspects related to the volatile composition of these distillates, the origin and presence of methanol, and the techniques used for quantification are also described. The methanol levels found in the different types of spirits are those expected based on the specific raw materials of each and, almost in all studies, respect the legal limits.
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Due to legal regulations, the rise of globalised (online) commerce and the need for public health protection, the analysis of spirit drinks (alcoholic beverages >15% vol) is a task with growing importance for governmental and commercial laboratories. In this article a newly developed method using nuclear magnetic resonance (NMR) spectroscopy for the simultaneous determination of 15 substances relevant to assessing the quality and authenticity of spirit drinks is described. The new method starts with a simple and rapid sample preparation and does not need an internal standard. For each sample, a group of 1 H-NMR spectra is recorded, among them a two-dimensional spectrum for analyte identification and one-dimensional spectra with suppression of solvent signals for quantification. Using the Pulse Length Based Concentration Determination (PULCON) method, concentrations are calculated from curve fits of the characteristic signals for each analyte. The optimisation of the spectra, their evaluation and the transfer of the results are done fully automatically. Glucose, fructose, sucrose, acetic acid, citric acid, formic acid, ethyl acetate, ethyl lactate, acetaldehyde, methanol, n-propanol, isobutanol, isopentanol, 2-phenylethanol and 5-(hydroxymethyl)furfural (HMF) can be quantified with an overall accuracy better than 8%. This new NMR-based targeted quantification method enables the simultaneous and efficient quantification of relevant spirit drinks ingredients in their typical concentration ranges in one process with good accuracy. It has proven to be a reliable method for all kinds of spirit drinks in routine food control.
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Coffee fruit production is an important agricultural sector in more than 70 tropical countries. However, the production of fruit spirits based on coffee fruits has not been investigated to date. This study evaluated, for the first time, its fermentation and distillation performance, ethanol yield and sensorial attributes. A selected yeast strain (Saccharomyces cerevisiae L.) fermented coffee cherry mash within five days and produced ethanol concentrations of 31.0 g/L. The mash was distilled and distillate fractions were categorized for heads/hearts/tails by sensory evaluation, resulting in an ethanol mass ratio of 1.0:4.2:0.8 with a total yield of 1.8% (w/w) ethanol based on coffee cherry mash. Analysis of fermentative volatiles indicated comparatively high methanol contents of 26 ± 4 g/L ethanol in the hearts fraction. Sensory evaluation of the hearts fraction resulted in 15 spirit specific descriptors, with vegetal and nutty indicating the most important terms to describe the perception of coffee cherry spirit. The results suggested that there is a high potential to introduce a fruit spirit based on coffee fruits.
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Alcohol adversely affects people around the world on a large scale even in non‐pandemic times, with about three million deaths attributed to alcohol use each year (Shield et al., 2020). During the current coronavirus disease (COVID‐19) pandemic, a variety of government reactions related to alcohol control were seen, with some countries banning the sale of alcohol outright, and others formally declaring off‐premises sales and alcohol delivery services to be “essential,” allowing for additional forms of delivery and weakened restrictions on its availability (Rehm et al., 2020, Reynolds and Wilkinson, 2020).
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The coffee plant Coffea spp. offers much more than the well-known drink made from the roasted coffee bean. During its cultivation and production, a wide variety of by-products are accrued, most of which are currently unused, thermally recycled, or used as animal feed. The aim of this review is to provide an overview of novel coffee products in the food sector and their current legal classification in the European Union (EU). For this purpose, we have reviewed the literature on the composition and safety of coffee flowers, leaves, pulp, husk, parchment, green coffee, silver skin, and spent coffee grounds. Some of these products have a history of consumption in Europe (green coffee), while others have already been used as traditional food in non-EU-member countries (coffee leaves, notification currently pending), or an application for authorization as novel food has already been submitted (husks, flour from spent coffee grounds). For the other products, toxicity and/or safety data appear to be lacking, necessitating further studies to fulfill the requirements of novel food applications.
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Coffee is one of the most important commodities worldwide. The industrial processing of coffee cherries generates a considerable volume of by-products such as wastewater, coffee pulp, mucilage, and husk. These by-products have sugars and nutrients that can be converted into value-added products via microbial action. In this study, for the first time, we evaluated the potential of coffee pulp and coffee wastewater as substrate for alcoholic fermentation produce a distilled beverage. The must composed by dry or wet coffee pulp and coffee wastewater added of commercial sucrose or sugarcane molasses was fermented by S. cerevisiae. After a screening step, a larger fermentation was carried out with the wet pulp added of sucrose due to its higher alcoholic fermentation efficiency. The distilled beverage contained 38% (v/v) ethanol and 0.2 g/L of acetic acid. The contaminants furfural, hydroxymethylfurfural and ethyl carbamate were below detection level. Among the 48 volatile compounds detected, the majority (21) were ethyl esters usually associated with floral and sweet aromas. Ethyl decanoate (996.88 µg/L) and ethyl dodecanoate (1088.09 µg/L) were the most abundant esters. Coffee spirit presented taste acceptance of 80% and sugarcane spirit, 70%. The tasters indicated an aroma acceptance of 86% for the coffee spirit and 78% for the sugarcane spirit. The results of this work demonstrate the potential for using coffee by-products to produce a good quality distilled beverage. Considering our results, especially sensorial analysis, we can infer that the produced coffee beverage represents a new alternative for adding value to the coffee production chain.
Objective: About 25% of global alcohol consumption is unrecorded, that is, concerns alcohol not registered in the country where it is consumed. Unrecorded alcohol includes homemade, illicit, or surrogate alcohols. The aim of this review is to update the evidence on unrecorded alcohol and its impact on health. Method: A narrative review and qualitative synthesis of scientific literature (English and Russian) for the period 2016-2020 was conducted. Results: A total of 100 articles were included in the synthesis. The most harm because of unrecorded alcohol seems to be caused by ethanol, although single and mass methanol poisonings constitute exceptions. Nevertheless, unrecorded consumption is associated with disproportionate harm that goes beyond toxicity, which is linked to hazardous drinking patterns of unrecorded alcohol, and its association with alcohol use disorders and social marginalization. The online sale of unrecorded alcohol, which circumvents alcohol availability regulations, is an emerging and not yet well-explored issue. Conclusions: Policy options include restricting access to methanol, increasing taxation, denaturing ethanol-containing liquids that could be used as surrogates, introducing more effective and less toxic denaturizing additives, and improving monitoring systems for fraud, tax evasion, and local sales restrictions, including raising the minimum legal drinking age. These measures should be implemented within a holistic policy framework to avoid unintended effects, such as an increase in total alcohol consumption, shifts from certain types of unrecorded products to potentially toxic alternatives, or limiting economic activity and jeopardizing the livelihoods of vulnerable populations (e.g., women comprise the majority of those making homebrew in some countries).
Coffee pulp is one of the major underutilized byproduct of coffee processing in farm level. Disposal of this agro-industrial waste has become one of the most challenging tasks for coffee planters. However, most of the efforts are towards the management of coffee pulp as an effluent, and not-on re-use. The problem is compounded due to the large volumes produced in diluted forms, which makes it expensive to reuse. The preliminary proximate analysis of coffee pulp indicated it to be rich in pectin and polyphenols. The efficacy of various chemicals like ethanol, sulfuric acid, hydrochloric acid, nitric acid, ammonium oxalate and metal salts for effective precipitation of pectin from coffee pulp was evaluated. HPLC characterization of the extracted and concentrated polyphenols fractions was analyzed. The maximum extraction of pectin was achieved by using metal salts and ethanol with 6.0% and 6.7% on wet weight basis respectively. The equivalent weight of extracted pectin (1180.5 mg/g) was found to be higher than that of commercial pectin (724.8 mg/g). The methoxyl content of the commercial pectin and crude pectin were 9.3 and 5.6% respectively. Gallic, vanillin, catechin, ethyl catechol, coumaric, Caffeic, and ferulic acid were the major polyphenols as quantified by the HPLC. The polyphenol fraction showed a good antioxidant activity with phosphomolybdate, FRAP, DPPH, and ABTS radicals respectively. The sustainable utilization of coffee pulp as a source of pectin and polyphenols with good antioxidant activities could help to solve the problem of waste generated in coffee processing in farm level.
About 0.5 ton of coffee pulp is generated for each ton of coffee cherry processed. In the present study, this waste was investigated as a source of pectin. Coffea arabica L. pulp was dried, treated with ethanol and the pectin extracted with 0.1 M HNO3 (14.6 % yield). Chromatographic, colorimetric and spectroscopic methods were used for pectin characterization. It had 79.5 % galacturonic acid, high methoxyl content (63.2 %), low levels of acetylation, protein and phenolics and Mw of 3.921 × 10⁵ g/mol. The pectin from coffee pulp was able to form gels with high concentration of sucrose or xylitol and low pH. The effect of pH (1.5–3.0), concentrations of pectin (0.5–2.5 %), sucrose (55–65 %) and xylitol (55–60 %) on the viscoelastic properties was investigated. Gels prepared with xylitol diplayed similar viscoelastic behavior to the gels prepared with sucrose. The results demonstrated that coffee pulp is a potential source of commercial pectin with gelling properties.
The World Health Organization estimates that globally out of the 6.2 L of pure alcohol consumed per person (15 + years), 25% is unrecorded alcohol. Unrecorded alcohol is defined as alcohol not registered in the legislation where it is consumed and includes homemade, surrogate, and counterfeit alcohols. Since the production, distribution, and consumption of unrecorded alcohol is not under official quality control and regulation, the risk of unrecorded alcohol containing potentially hazardous substances [e.g., methanol, acetaldehyde, aflatoxins, heavy metals, toxic denaturants such as diethyl phthalate (DEP)] may be higher than that for recorded alcoholic beverages. Consequently, the consumption of such beverages may expose drinkers to morbidity and mortality. For example, research conducted in 2017 on Kenyan artisanal beers collected from slums found 50% aflatoxin contamination. In this chapter we extensively review the epidemiology, chemical composition, health consequences citing a case story of the problem of unrecorded alcohol from Kenya, and also suggest plausible policy interventions to address the challenges posed by unrecorded alcohol.