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Research on 2-methoxy-3-isobutylpyrazine in grapes and wines

(School of Oenology, University of Bordeaux II)
Pyrazines (1,4-diazines) are nitrogen-containing heterocyclic compounds that are quite widely
distributed in nature in both the animal and plant kingdoms. The food industry is the area in
which these compounds have been the most extensively studied. They are considered to be
the heterocyclic compounds most widely represented in food aromas (Vernin and Vernin,
1982). They can be classified into three groups depending on their origins: those formed by
heat treatment, those formed by micro-organisms and those present in the natural state in
plants. Amongst the methoxypyrazines in the last category, the most important ones are 2-
methoxy-3-isopropylpyrazine (IPMP), 2-methoxy-3-sec-butylpyrazine (s-BMP) and 2-
methoxy-3-isobutylpyrazine (IBMP). IBMP was identified for the first time in green pepper
(Capsicum annuum var. grossum) by Buttery et al. (1969). Its detection threshold in water is
estimated to be 2 ng/L, and those authors consider it to be responsible for the characteristic
aroma of green peppers. It was subsequently identified in several raw vegetables such as chili
peppers (Capsicum frutescens), beans (Phaseolus vulgaris), broad beans (Vicia faba), lettuce
(Lactuca sativa), spinach (Spinacea oleracea), etc. (Murray and Whitfield, 1975). Those
authors note that one of the other methoxypyrazines is often dominant in some species. This is
the case for IPMP in asparagus (Asparagus officinalis), peas (Pisum sativum), cucumber
(Cucumis sativus), lettuce, potatoes (Solanum tuberosum) or even sow-thistle (Sonchus
oleraceus) and for s-BMP in beets and carrots (Daucus carota sativa).
In 1975, IBMP was identified for the first time in Cabernet Sauvignon grapes (Vitis
vinifera L. cv. Cabernet Sauvignon) by Bayonove and Cordonnier, who claimed that it was
responsible for the green pepper aroma that is characteristic of this variety. In 1982, Augustyn
et al. identified IBMP in Sauvignon blanc grapes (Vitis vinifera L. cv. Sauvignon blanc). Over
the last 10 to 15 years, its contribution to the vegetal and green pepper aromas of Cabernet
Sauvignon, Merlot and Sauvignon blanc wines has been demonstrated (Harris et al., 1987;
Maga, 1989; Allen et al., 1989; Allen et al., 1991; Allen et al., 1994; Kotseridis et al., 1998;
Roujou de Boubée et al., 2000). These authors also show that s-BMP is rarely detected in
wines, whereas IPMP is found at levels below its detection threshold in water (2 ng/L). As
such, 2-methoxy-3-isobutylpyrazine would seem to be the key compound involved in the
green pepper aroma of Cabernet Sauvignon, Sauvignon blanc and some Merlot wines. With
these varietals, the IBMP concentration significantly exceeds the detection threshold.
This compound is present in grapes, it has no known precursor and its concentration
decreases during ripening (Allen et al., 1989; Lacey et al., 1991) under the influence of light
(Heymann, 1986; Allen and Lacey, 1993; Hashizume and Samuta, 1999). Consequently, a
high concentration in grapes at harvest is associated with a lack of ripeness and has a
negative impact on wine aroma quality. Winemakers and oenologists commonly associate
such aroma characteristics in grapes with low anthocyanin content and with mediocre “tannin
It is therefore crucial to know what conditions influence IBMP concentration in grapes
and wine. In this paper, we present the results of our research on the methoxypyrazine aroma
of wines and on the conditions under which IBMP forms or breaks down in the grapevine.
1. The Methoxypyrazine Character of Wines and Its Evolution during Winemaking
and Ageing
1.1. The Organoleptic Impact of 2-Methoxy-3-Isobutylpyrazine in Wines and Its
Distribution in Wines of Different Varieties
The quantification method that we developed (Roujou de Boubée et al., 2000) is based on
that developed by Harris et al. in 1987 and then used by Allen et al. in 1994. By improving
the ease and rapidity of extract preparation, we have been able to perform analyses with good
repeatability on relatively large series of samples.
In oenology, the value of interest is the threshold beyond which the green pepper aroma
caused by IBMP becomes perceptible in wine. However, the determination of a detection
threshold in wine does not yield an indicative value, owing to the great variations in
composition from one wine to another and in descriptors used from one taster to another. As
such, we sought to establish not a threshold value for a given wine, but rather a representative
threshold for a given wine type, in our case a red Bordeaux-type wine. To do this, 50 red
wines from Bordeaux and the Loire Valley (Cabernet Sauvignon, Cabernet franc and Merlot
varieties from several different vintages for the Bordeaux wines; Cabernet franc from the
1991 and 1992 vintages for the Loire Valley) were evaluated by a panel of 10 persons at the
Bordeaux School of Oenology. The wines were noted on a scale of 0 to 5 for the intensity of
their green pepper aroma. The median of the scores for each wine was calculated and then
correlated with the IBMP content determined by gas chromatography coupled with mass
spectrometry (GC/MS). The relationship is linear between the median scores and the IBMP
contents (r_ = 0.739, p>0.01%) (Figure 1). Wines with no green pepper aroma (median=0)
contain 10 ng/L of IBMP on average. Those with only a slight green pepper aroma
(median=1) have an average content of 15 ng/L, whereas beyond this level, the perception of
the green pepper aroma is medium to strong.
Figure 1: Correlation between the median of tasting scores obtained with 50 red wines from
Bordeaux and the Loire Valley and the concentration of 2-methoxy-3-isobutylpyrazine as
determined by GC/MS.
We can therefore estimate that the detection threshold for the green pepper aroma, also known
as the methoxypyrazine aroma, is 15 ng/L of IBMP in red Bordeaux and Loire Valley wines.
In other words, this is the concentration at which the tasters identify a vegetal aroma in those
We then performed a statistical study on 96 red and white wines made from the Cabernet
Sauvignon, Cabernet franc, Merlot and Sauvignon blanc varieties in order to determine those
y = 0.1533x - 1.3106
R2 = 0.7389
0 5 10 15 20 25 30 35 40
[IBMP] (ng/L)
Median of tasting scores
in which IBMP plays a role in the vegetal aroma. This study shows that IBMP is the main
contributor to the vegetal aroma in Cabernet Sauvignon, Cabernet franc and Sauvignon blanc
wines. However, this compound is perceptible in only a minority of Merlot wines.
Once the methoxypyrazine character had been defined, its threshold determined and the grape
varieties identified, we focused on how the IBMP content changes during the winemaking
1.2. Extractability of 2-Methoxy-3-Isobutylpyrazine during Winemaking.
Observations on the Evolution of IBMP Content in Wines during Bottle Ageing.
Whole clusters of manually harvested Sauvignon blanc grapes were placed in a pneumatic
press (Bücher, 70 hL). The juice samples obtained by simple crushing of the berries during
press filling and at the beginning of the press cycle (0.2 bar; 30 min) had the highest IBMP
contents (Table 1).
Table 1: IBMP concentration (ng/L) of Sauvignon blanc musts sampled at different press
levels during the 1998 harvest.
Pressure Level
Batch 2
Free run 0.2 bar (30 min)
Free run 0.2 bar (60 min)
0.8 bar (90 min)
1.4 bar (120 min)
2 bar (140 min)
2 bar (180 min)
The musts extracted subsequently contain less IBMP, and as the volume of liquid is lower,
these fractions contribute less to the final IBMP content. The final IBMP concentration differs
little from that of the first free-run juice obtained during press filling. IBMP is easily extracted
from grape clusters during crushing and at the beginning of pressing, at least in the case of
pneumatic pressing of whole clusters.
Table 2 shows the effect of settling on the IBMP content of musts.
Table 2 : Effect of settling on the IBMP concentration (ng/L) of Sauvignon blanc musts
Batch 1
Batch 2
Before settling
After settling (200 NTU)
The clarified musts (200 NTU) contain about half as much methoxypyrazine as the unsettled
musts. A part of the IBMP seems to interact with the grape solids and is thus eliminated by
must clarification. It has previously been observed that settling limits the grassy aroma of
white musts by lowering the contents of C6 aldehydes and alcohols (Dubourdieu et al., 1986)
and of methionol (Lavigne, 1996). The effect of settling on IBMP content in musts has never
been reported before.
Under real conditions, the IBMP contents of Cabernet Sauvignon 24 hours after
tanking-down and at the end of maceration are not very different (Figure 2). Most of the
IBMP in the free-run wine is therefore extracted into the aqueous phase prior to alcohol
Figure 2: Evolution of the IBMP concentration during winemaking with Cabernet Sauvignon
grapes in 1997 (CS 97) and 1998 (CS1 98 and CS2 98).
To monitor the kinetics of IBMP extraction as precisely as possible with Cabernet
Sauvignon grapes, a micro-batch of wine was made in the laboratory (7 kg of grapes in 15-
litre stainless steel drums).
Figure 3: Evolution of the IBMP concentration during micro-batch winemaking from
Cabernet Sauvignon grapes in 1999 (CS 99).
The extraction of IBMP from the grapes into the must is even quicker in this case
(Figure 3). Within 24 hours, before the alcohol fermentation even begins, all of the IBMP
found in the wine after racking has already been extracted from the grapes. The IBMP content
is not increased by the successive punching-down operations performed during fermentation
nor by post-fermentation maceration. Finally, the final concentration of the wine after racking
does not seem to be influenced much by the frequency of pump-overs or by the skin contact
time. However, as Kotséridis et al. (1999) observed, the IBMP content of the press wine can
be greater than that of the free-run wine (Table 3). As such, IBMP certainly participates in the
1 2 3 4 5 7 8 9 14 15 16 17 18 23
Days after tanking down
IBMP (ng/L)
CS 97 CS1 98 CS2 98
End AF
Time (h)
IBMP (ng/L)
increased vegetal character of many press wines. A certain fraction of the IBMP associated
with the solid parts of the grapes can therefore be extracted during the mechanical operations
of pressing.
Table 3: Evolution of the IBMP concentration (ng/L) in Cabernet Sauvignon press wines
(1998) during the press cycle. Batches 1 and 2.
Batch 1
Batch 2
Start of pressing (0.2 bar)
Pressing after 1 hr. (0.8 bar)
Pressing after 2 hrs. (2 bar)
Quite often, it can be observed that the thermovinification of red grapes (heating of the
grapes to between 60 and 80°C for a short period to promote extraction of phenolic
compounds and to destroy oxidases) leads to a decrease in the vegetal character of some
wines. Of the 5 examples presented (Table 4), thermovinification systematically decreases the
IBMP concentration to below the 15 ng/L threshold, and as such the vegetal character is no
longer perceptible in those wines. This decreases varies from 29 to 67%, depending on the
Table 4: Influence of thermovinification on the IBMP content (ng/L) of 5 Cabernet Sauvignon
Wine 1
Wine 2
Wine 3
Wine 4
Wine 5
We thus sought to provide an analytical interpretation for an empirical observation. In
the laboratory, a Cabernet Sauvignon must doped with IBMP was heated by means of a water
bath to 60°C in a flask connected to a rotary vacuum evaporator in order to recover the
volatilised fraction. It was shown that all of the IBMP that disappeared from the must was
found in the evaporated fraction, which shows that this compound is volatilised during
heating (boiling point of IBMP = 50°C). Thermovinification can be of interest in cases where
the grapes have not reached optimal ripeness for different reasons (difficult weather
conditions, unfavourable soil/exposure, excessive yield, etc.) or where the grapes are mouldy.
This technique can lead to highly coloured, supple, fruity (ester-type) and less vegetal wines.
The evolution of IBMP content for one Cabernet Sauvignon wine and one Sauvignon
blanc wine during bottle ageing was also monitored. After three years of ageing in a dark
cellar, no significant change was recorded. The chemical stability of IBMP explains this
result. Thus, one should not count on time to diminish this olfactory defect in the bottle.
The aroma of Sauvignon blanc or Muscat wines is determined by the grape ripening
conditions and also, in large part, by the winemaking conditions (Peyrot des Gachons, 2000;
Günata, 1984). For the Bordeaux varieties, we show here that obtaining fruity wines with no
vegetal character depends mostly on the grape ripening conditions. This means that to get a
low IBMP concentration in the wines, it is imperative to understand what happens prior to the
harvest. What is the metabolism for IBMP in the grapevine? In what parts of the grapevine is
this compound found? How does its concentration change during the reproductive cycle and
what factors affect it?
2. Evolution and Location of 2-Methoxy-3-Isobutylpyrazine in Various Grapevine
Organs during the Reproductive Cycle
2.1. From Fruit Set to Veraison
The determination of IBMP content in grape berries at an early stage (prior to veraison)
enables us to observe a synthesis phase preceding the start of veraison (Figure 4), as
previously reported by Hashizume and Samuta (1999).
Figure 4 : Evolution of IBMP content in Cabernet Sauvignon grapes from berry touch to
veraison (1999).
Normally, the breakdown of IBMP is rapid initially and then it slows down as harvest
approaches. However, in 1999, we observed in this vineyard block that the IBMP content
increased in the berries between 31 July and 12 August (mid-veraison). This phenomenon,
which had never been observed previously, is related to specific weather conditions. Between
27 July and 10 August, approximately 180 mm of rain fell on the block. The soil water
reserves were thus restored, and the grapevines, which had been close to the end of their
growth cycle, began to grow again. These vineyard observations do not enable us to draw any
definitive conclusions. However, it would seem that IBMP synthesis is related to the
vegetative growth of the grapevine. This could explain why vigorous vines that stop growing
relatively late in the season produce grapes that generally have high IBMP levels. This result
should, however, be compared with those we obtained in the following experiment set up by
researchers at INRA Bordeaux (Tandonnet et al., 1996). A block of Cabernet Sauvignon vines
was subjected to three soil-water statuses: normal (vintage conditions), irrigated (the vines
received 4.6 mm of water/day from late June to late August) and dry (the soil was covered
with a tarp from late June to harvest time). The grapes were vinified in small batches, and the
IBMP concentrations were determined in the wines in 1994, 1995 and 1996 (Figure 5). We
can note that irrigation leads to a significant increase in IBMP concentration in the wines
12-Jul 17-Jul 22-Jul 27-Jul 01-Aug 06-Aug 11-Aug 16-Aug 21-Aug
[IBMP] (ng/L)
(+79% in 1994 and +39% in 1996 with respect to the “normal” wines). In 1996, tarping-over
at soil level led to a 57% decrease in the wine IBMP levels with respect to the “normal”
wines. Perhaps by inducing high vine vigour, irrigation leads to greater IBMP synthesis.
Figure 5 : Effect of different soil water statuses on IBMP concentration for Cabernet
Sauvignon wines in 1994, 1995 and 1996 (normal: vintage conditions; irrigated: 4.6 mm of
water per day from late June until veraison in late August; dry: tarping-over at soil level under
the vines from late June until ripeness).
Regardless of the cause, IBMP synthesis seems to occur between fruit set and two to
three weeks prior to the onset of veraison. At this stage, the stems contain a large proportion
of IBMP (Figure 6). Inside the berry, IBMP is found mainly in the skin (72%) and also in the
seeds (23.8%). The pulp contains very little IBMP (4.2%).
At this stage, IBMP is found in the berries, but we cannot determine if it is synthesised
in situ. IBMP has in fact been identified in Cabernet Sauvignon leaves at the time of grape
harvest (Hashizume et al., 1997). This finding suggests that IBMP could be synthesised in the
leaves. We have therefore examined whether IBMP is present in the leaves upon berry touch.
During this analysis, the clusters were grouped as a function of their insertion point on the
shoot. On the primary shoot, we distinguished between leaves in the basal area (the first three
to four leaves from the base), the leaves in the intermediate zone and the leaves in the apical
zone where growth has not finished.
Figure 6: Location of IBMP in different components of Cabernet Sauvignon grape clusters
prior to veraison (4/08) in 1999.
Normal Irrigated Dry
[IBMP] (ng/L)
Skins Pulp Seeds Stems
The leaves on the secondary shoots (or summer laterals) were also divided into groups.
Firstly, we show that the leaves contain IBMP at this stage (Figure 7). They are therefore
capable of synthesising this compound. Secondly, we can note that the basal leaves have a
very high IBMP content, i.e. much greater than in the other leaves or in the clusters.
Basal l.
Middle l.
Apical l.
Lateral l.
Figure 7: IBMP content in clusters and leaves (l.) at different levels of Cabernet Sauvignon
shoots (30/07/1999).
Knowing that many products synthesised in the leaves are then transported to the berries, we
decided that it would be interesting to determine whether IBMP is transported from the leaves
to the clusters. To do this, we used fruit-bearing cuttings of Sauvignon blanc obtained in
accordance with the protocol described by Ollat et al. (1998a) and Gény et al. (1998). Twelve
fruit-bearing cuttings of Sauvignon blanc (4 cuttings _ 3 repetitions A, B and C), each with
one cluster, were selected between the small-pea stage and the beginning of veraison for their
homogeneity (physiological stage, cluster size and compactness). On each of the cuttings,
eight leaves were selected from all along the shoot. Each leaf was placed in a plastic container
and then treated with a solution of 2(2H3)methoxy-3-isobutylpyrazine (1 mg/L), which is the
deuteriated analogue of IBMP and is used as an internal standard for GC/MS. The deuteriated
analogue solution of IBMP was deposited on the leaf every morning and evening for three
days. On the fourth day, the clusters were harvested. For the leaves treated with the
deuteriated IBMP solution, the leaf blade was removed (to avoid any contamination risk).
Only the petiole was sampled. The leaves not treated with deuteriated IBMP (i.e. the young
leaves near the apex) as well as the apices were sampled and gathered together. Finally, the
clusters were picked.
The distribution of deuteriated IBMP in the shoot was then measured (Figure 8). Firstly,
we can note that the deuteriated IBMP is detected in the petioles, which shows that it
penetrated the leaf blade and that it was transported. The great quantity of deuteriated
methoxypyrazine found in the petioles for repetition C (80%) seems to indicate that the
compound deposited on the leaf had not yet fully migrated towards the other plant organs. For
the three repetitions, we can also observe a low level of redistribution to the growing parts of
the vine (i.e. young leaves and apex, which always contain less than 10%). This corroborates
the fact that at this stage, the cluster is the organ to which metabolites are preferentially
Figure 8: Distribution (in %) for three repetitions (A, B, C) of deuteriated IBMP treatment on
Sauvignon blanc shoots after deposition on the leaves and migration.
1 repetition = 4 cuttings.
Finally, we found deuteriated IBMP in the stems and then in the berries. We therefore
demonstrate that this compound is transported by the phloem from the leaves to the berries.
Knowing that leaves contain high IBMP levels during ripening and that this compound
can migrate from the leaves to the clusters, we can imagine that the leaves form IBMP
reserves that can supply the clusters. We can also postulate that the berries are also capable of
synthesising methoxypyrazine. Before veraison, synthesis seems to occur faster than
breakdown. Perhaps at this stage, the berries have not yet acquired the capacity to break down
IBMP (or only at very low levels). The IBMP content in the berries would thus be the result
of transport from the leaves and of synthesis in situ.
Unfortunately, no advances have been made in the field of IBMP biosynthesis in plants,
and even the origin of this compound remains unknown. Murray et al. (1970) put forth the
hypothesis of a condensation between glyoxal (which is also involved in the formation of
other methoxypyrazines, according to these authors) and leucine (after having accepted an
amide group). In line with this hypothesis, a study on the biosynthesis of 2-methoxy-3-
isobutylpyrazine was undertaken using cell cultures of Cabernet Sauvignon. For the first time,
we demonstrate that an undifferentiated callus of Cabernet Sauvignon is capable of
synthesising IBMP. Moreover, adding leucine, i.e. the supposed precursor of IBMP, to the
culture medium increases IBMP production by the cells. However, in one experiment, the
addition of stable isotopes (L-leucine-d10 and 15NH4Cl) did not lead to isotopic enrichment of
the IBMP produced by the cells.
From fruit set up through about two to three weeks before mid-veraison, IBMP is
synthesised and accumulates in the leaves and/or berries, perhaps from leucine. Thereafter,
the IBMP content drops up through harvest.
2.2. From Veraison to Ripeness
The shape of IBMP content curves during ripening does not change as a function of
whether this content is expressed as ng/L, ng/kg of fresh matter or pg/berry (Figure 9).
0% 20% 40% 60% 80% 100%
Apical zone Petiole Stems Berries
Figure 9: Evolution of IBMP content (expressed in ng/L, in ng/kg of fresh matter or in
pg/berry) in Cabernet Sauvignon grapes from berry touch till harvest (1999). Mid-veraison
occurred on 11 August.
As such, and in contrast with what occurs with tartaric acid, for example, the decrease in
IBMP content expressed in ng/L is independent of the dilution that occurs through the
increase in berry volume during this period. This compound is thus truly broken down during
ripening. Several studies have revealed a strong relationship between exposure of the cluster
to light and the decrease in IBMP concentration (Allen and Lacey, 1993; Noble et al., 1995;
Hashizume and Samuta, 1999). They thus confirm the first studies performed by Heymann
(1986) and then by Maga (1989), which showed that methoxypyrazines are broken down by
A photo-degradation study of IBMP in a solvent (methanol, 10% v/v) and in wine
(white and red) enabled us to confirm that it breaks down when it is exposed to normal
daytime sunlight. We then showed that the breakdown products (including 2-methoxy-3-
methylpyrazine, which has been identified as a reaction intermediate) are present in very low
quantities and do not seem to have an organoleptic impact. Until now, it was possible to
suppose that an IBMP breakdown product could be involved in the aroma of Cabernet
Sauvignon wines. While this variety has a strong green pepper aroma when unripe, this
vegetal character disappears when conditions permit it and only then can a great Cabernet
Sauvignon wine with fruity and toasty aromas be made. Our work seems to show that the
origin of these aromas is not directly related to IBMP breakdown.
12-Jul 22-Jul 01-Aug 11-Aug 21-Aug 31-Aug 10-Sep 20-Sep 30-Sep
ng/kg of FM
As we have seen, prior to veraison, IBMP begins to break down in the berries. However, the
distribution of this compound in the clusters remains the same throughout ripening (Figure
Figure 10: Distribution (in %) of IBMP in different components of Cabernet Sauvignon
clusters during ripening in 1999.
Regardless of the phenological stage, the pulp contains little IBMP and the stems contain a
lot. However, from veraison to harvest, the proportion of IBMP decreases in the stems and
increases in the skins. It also decreases slightly in the seeds during this period.
Upon harvest, IBMP is found mainly in the stems. As such, we can understand why the
green pepper character in a wine can be greatly influenced by destemming quality. Between
11 August and 23 September, the IBMP content increases most in the basal and intermediate
leaves (Figure 11). In fact, the IBMP concentration in the adult leaves evolves in the opposite
direction from that of the grapes. This result may appear paradoxical. Under identical
environmental conditions, IBMP accumulates in the leaves, whereas it is broken down in the
grapes during ripening. If IBMP is broken down by light, why is it that the basal leaves,
which receive as much if not more light than the clusters, display increasing levels of IBMP
during the ripening phase? Everything suggests that the metabolism of this compound is
different in the fruit and in the leaves.
0% 20% 40% 60% 80% 100%
After veraison
Before veraison
Stems Skins Seeds Pulp
Adult leaves
Middle leaves
Young leaves
[IBMP] (ng/kg of FM)
Figure 11: IBMP in the clusters and leaves (l.) at different insertion levels on the shoot during
ripening of Cabernet Sauvignon (1999).
These results confirm the advantages of leaf removal from the grapevine to decrease the
vegetal/green pepper aromas of grapes. By exposing the grapes to greater sunlight, leaf
removal increases IBMP breakdown, and it might also decrease the IBMP content in the
berries by removing organs that could be a source of IBMP supply for the clusters.
2.3. Effect of Vineyard Practices and Conditions on IBMP Content in Grapes
First, we measured the cumulative effect of all summer pruning and thinning work on
the IBMP content of Cabernet Sauvignon and Merlot grapes. This work includes debudding
(between budbreak and bloom), removal of summer laterals in the cluster zones on the east
side of the vine row (at the end of fruit set), leaf thinning in the fruiting zone on the east side
(at berry touch) and cluster thinning to limit the yield to around 50 hL/ha (at the start of
Table 5: Influence of summer pruning and thinning (SPT) work on the composition of Merlot
(M) and Cabernet-Sauvignon (CS) wines, 1997.
% vol.
Total acidity
(g/L H2SO4 )
M control
CS control
TPI: Total Polyphenolic Index
Summer pruning and thinning has a direct effect on decreasing the IBMP content of
Cabernet Sauvignon and Merlot grapes, from veraison till harvest. The photolabile nature of
IBMP explains this result. Grapes from the control group and from the thinned group were
vinified on a large scale (311-hL tanks) and then analysed at the start of ageing (Table 5). The
differences are more marked for Cabernet Sauvignon. The wine made from the “test” vines
(i.e. the thinned vines) has more alcohol, a higher phenolic content (+40% anthocyanins) and
its IBMP content is much lower than that of the wine made from the “control” vines (-39%).
The “control” wine is clearly marked by the green pepper aroma of IBMP, whereas IBMP is
not perceptible in the “test” wine.
It is widely acknowledged that the grapevine reacts differently depending on the date on
which summer vine work is performed. An experiment was conducted in 1998 on Cabernet
Sauvignon and Sauvignon blanc vines in order to determine how the timing of summer vine
work (summer lateral removal and leaf thinning in the cluster zone on the east side) affects
the IBMP content of grapes at harvest. This experiment led to the following conclusions. It is
generally important to perform lateral removal and leaf thinning early, i.e. between fruit set
and berry touch. If this is done, the grapes have a higher sugar content at harvest, they are
smaller in size and they contain less IBMP (Table 6). Late leaf thinning, while it does increase
the sugar content in the grapes, does not lead to a sufficiently great decrease in IBMP content
(this content is 65% greater than for a vine on which the leaf thinning and lateral removal
were done early).
Table 6: Influence of the timing of summer pruning and thinning (difference with respect to a
control group) on the composition of Cabernet Sauvignon grapes upon harvest – 1998.
Summer lateral removal
Lateral removal at fruit set
Lateral removal and leaf
& leaf thinning at fruit set
& leaf thinning after veraison
thinning after veraison
Not significant
Not significant
Not significant
There are no significant differences in grape composition at harvest if this work is performed
at fruit set or when the berries are the size of small peas. In both cases, the work improves
ripening. From a practical point of view, this offers greater flexibility in scheduling summer
vine work. There is a 15-20 day period in which one can perform this work without affecting
final grape quality. Once this period is over, the risk becomes greater of harvesting grapes
with marked green pepper aromas. These results were obtained in the case of low-trained
vines with high planting density (8,550 vines/ha) and also with high-trained vines with low
density (3,300 vines/ha). Analogous results were found with Sauvignon blanc.
However, these results obtained in 1998 were not confirmed in 1999, when the IBMP
contents in the grapes at harvest were close to zero, regardless of when the summer vine work
was performed. The 1999 vintage was an atypical year, with heavy rainfall during veraison,
which lengthened the veraison period and led to heterogeneity in berry ripeness. Thereafter,
the weather was variable, with storms being intermixed with sunny, hot periods. These
weather conditions led to unusual vine function. We can observe that IBMP breakdown was
slower in 1999 than in 1998. The main difference between these two vintages lies in the
IBMP content at mid-veraison: it was three times greater in 1998 for the same vineyard block.
In other words, for vintages like 1998, it is important to intervene early so that the IBMP in
the grapes breaks down as quickly as possible. However, in 1999, early leaf thinning
accelerated IBMP breakdown at the beginning, but at harvest no difference was observed
between the different lots (“test” and “control”), owing to the low levels of IBMP present
from the start.
This proves that it is not so much the weather conditions during the ripening period that
matter but rather those just prior to that period. It is probable that an early diagnosis (i.e. in
late July) of the grape IBMP content would help in determining whether or not lateral
removal or leaf thinning are needed in a vineyard block. While 1999 did not confirm the
observations made in 1998, lateral removal and leaf thinning are major vineyard techniques
enabling production of high-quality wine grapes. These practices are not widely used (since
they cannot be mechanised and are thus costly), but they can be advantageous if performed
early (at fruit set, the laterals are small and can be removed easily and quickly). Such
practices facilitate further summer vine work by eliminating some of the vegetation in the
fruiting zone; they improve the healthiness of the crop and lead to better aeration around the
clusters; they remove some of the organs requiring influx of nutrients and thus they promote
better redistribution of photosynthesis products for improved grape ripeness.
The application of an original protocol enabled us to define a upper limit for the IBMP
concentration beyond which the methoxypyrazine character is perceptible in red Bordeaux-
type wines. This level is on average 15 ng/L. We have been able to determine the contribution
of IBMP to the vegetal aroma of Bordeaux varieties. It plays a major role for Cabernet
Sauvignon, Cabernet franc and Sauvignon blanc and a minor one for Merlot.
We have also shown that the IBMP content of wine depends mainly on that of the
corresponding grapes and that it is only marginally affected by winemaking techniques. In the
case of traditional winemaking, IBMP is highly extractable, independently of pressing
conditions for white wines and of maceration time and the number of pump-overs for red
wines. Only the settling of Sauvignon blanc musts and a careful selection of press wines for
Cabernet Sauvignon can be used to limit the IBMP content of wines. In the case of
thermovinification, heating the grapes leads to a significant drop in IBMP concentration,
owing to volatilisation. We have observed no change in IBMP concentration in wines during
bottle ageing.
IBMP concentration increases in grapes from fruit set until about two to three weeks before
mid-veraison. This phenomenon seems to be influenced by the grapevine water status before
veraison. The use of Cabernet Sauvignon cell cultures has not enabled us to explain the
mechanisms of IBMP biosynthesis. Nevertheless, we have shown that the addition of leucine,
which is the supposed precursor of IBMP, leads to increased IBMP production. During this
period, IBMP is synthesised in the leaves, which is where it is mainly located. It is also in the
stems, skins and seeds (in order of decreasing importance). The pulp contains almost no
IBMP. We have revealed for the first time that IBMP is transported from the leaves to the
clusters during this stage.
The maximum IBMP content in the grape is reached before veraison. After this, the
compound begins to break down in the berries. The order of its distribution in the leaves and
clusters remains the same throughout the ripening period. This breakdown is the result of
IBMP’s sensitivity to light. However, none of the photo-degradation products, including 2-
methoxy-3-methylpyrazine, which we have identified here, appear to have any organoleptic
impact. Paradoxically, while it is broken down in the grapes, IBMP continues to accumulate
in the leaves. The metabolism of methoxypyrazine does not seem to be the same in leaves as
in clusters.
The IBMP content of grapes at harvest can be controlled by summer vine work. Operations
such as debudding, summer lateral removal, leaf thinning and cluster thinning lead to a large
decrease in IBMP content in Merlot and Cabernet Sauvignon grapes during ripening. It is
generally important to perform lateral removal and leaf thinning early, i.e. between fruit set
and berry touch. After that, the risks are greater of harvesting grapes with marked green
pepper aromas. The comparison of the results obtained in 1998 and 1999 enables us to
postulate that the key to the methoxypyrazine character of ripe grapes is related to the weather
conditions that prevail at an early stage and which lead to a certain initial IBMP content in the
grapes prior to veraison.
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... The form and concentration of MPs may vary depending on the grapevine part. For example, very high concentrations of MPs are found in grape roots (8000 ng/L), and these are primarily IPMP, whereas IBMP dominates in the berries, leaves, and shoots [24,25]. Older leaves have the highest IBMP concentrations, and they increase during grapevine growth as the season progresses [25]. ...
... For example, very high concentrations of MPs are found in grape roots (8000 ng/L), and these are primarily IPMP, whereas IBMP dominates in the berries, leaves, and shoots [24,25]. Older leaves have the highest IBMP concentrations, and they increase during grapevine growth as the season progresses [25]. In comparison, clusters, young leaves, and lateral shoots contain lower amounts of IBMP [25]. ...
... Older leaves have the highest IBMP concentrations, and they increase during grapevine growth as the season progresses [25]. In comparison, clusters, young leaves, and lateral shoots contain lower amounts of IBMP [25]. An analysis of the distribution of MPs in grape berries indicates that 72% of IBMP is found in the skin, 23.8% in the seeds and only 4.2% of IBMP in the pulp [25]. ...
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Alkyl-methoxypyrazines are an important class of odor-active molecules that contribute green, ‘unripe’ characters to wine and are considered undesirable in most wine styles. They are naturally occurring grape metabolites in many cultivars, but can also be derived from some Coccinel-lidae species when these ‘ladybugs’ are inadvertently introduced into the must during harvesting operations. The projected impacts of climate change are discussed, and we conclude that these include an altered alkyl-methoxypyrazine composition in grapes and wines in many wine regions. Thus, a careful consideration of how to manage them in both the vineyard and winery is important and timely. This review brings together the relevant literatures on viticultural and oenological inter-ventions aimed at mitigating alkyl-methoxypyrazine loads, and makes recommendations on their management with an aim to maintaining wine quality under a changing and challenging climate.
... Molecules 2020, 25, x FOR PEER REVIEW 8 of 20 Studies on the formation of the pyrazine ring in plants are scarcely found. On an Académie Amorim in 2003, Roujou de Boubée [57] issued the studies on IBMP in grapes and wines. He demonstrated that the addition of leucine in the media could promote the IBMP biosynthesis by the undifferentiated callus of Cabernet Sauvignon. ...
... Studies on the formation of the pyrazine ring in plants are scarcely found. On an Académie Amorim in 2003, Roujou de Boubée [57] issued the studies on IBMP in grapes and wines. He demonstrated that the addition of leucine in the media could promote the IBMP biosynthesis by the undifferentiated callus of Cabernet Sauvignon. ...
... Therefore, the two teams speculated that L-leucine may be one of the precursors of IBMP. However, the addition of stable isotopes (L-leucine-d 10 and 15 NH 4 Cl) did not lead to isotopic enrichment of the IBMP produced by the Cabernet Sauvignon callus [57]. Lei et al. [28] explained that the stable isotope was difficult to track accurately. ...
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3-Alkyl-2-methoxypyrazines (MPs) contribute to the herbaceous flavor characteristics of wine and are generally considered associated with poor-quality wine. To control the MPs in grapes and wine, an accurate understanding of MP metabolism is needed. This review covers factors affecting people in the perception of MPs. Also, the history of O-methyltransferases is revisited, and the present review discusses the MP biosynthesis, degradation, and biochemical regulation. We propose the existence of a cycle between MPs and 3-alkyl-2-hydropyrazines (HPs), which proceeds via O-(de)methylation steps. This cycle governs the MP contents of wines, which make the cycle the key participant in MP regulation by genes, environmental stimuli, and microbes. In conclusion, a comprehensive metabolic pathway on which the HP–MP cycle is centered is proposed after gaining insight into their metabolism and regulation. Some directions for future studies on MPs are also proposed in this paper.
... MPs are efficiently extracted by conventional red wine practices, and their concentrations in wine are strongly correlated to their concentrations in grapes (Ryona et al. 2009). Several studies have evaluated the efficacy of vinification and cellaring practices in reducing MPs (Blake et al. 2009, de Boubee 2003, Marais 1998, Pickering et al. 2006 and have generally concluded that remediation of MPs is ineffective or else results in other nonselective changes to the wine. Viticultural management strategies that reduce MPs in the vineyard have thus been proposed to be the most effective way to control MP concentration in wine (Bogart and Bisson 2006). ...
... These effects are generally hypothesized to be mediated through an increase of sunlight reaching the fruiting zone. Several groups have observed that cluster light exposure results in lower MP concentrations in mature fruit (Allen et al. 1996, de Boubee et al. 2002, de Boubee 2003, Marais et al. 1999, Noble et al. 1995, Ryona et al. 2008. Recent work suggests that sun-exposed clusters accumulate less IBMP preveraison than shaded clusters within the same vine (Ryona et al. 2008) and that the proportional differences persist until harvest, although the physiological mechanisms behind these effects are not understood. ...
... Most of the aforementioned studies have observed differences between shaded and exposed fruit by using artificial shading or taking advantage of natural variation in light exposure within the canopy, but little work has been published on the effectiveness of specific vineyard practices (e.g., leaf removal) to reduce MP accumulation preveraison and subsequent levels at harvest. A 68% reduction in IBMP concentration of Cabernet Sauvignon at harvest resulted from removal of lateral shoots and basal leaves on the east side of the fruiting zone at fruit set compared to an unthinned control (de Boubee 2003). A similar treatment imposed postveraison resulted in only a 10% reduction in IBMP at harvest. ...
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Field studies were conducted on Vitis vinifera L. cvs. Cabernet franc and Merlot to evaluate the effects of basal leaf removal timing and severity on 3-isobutyl-2-methoxypyrazine (IBMP) concentration in grape berries. Treatments consisted of removing either 50% or 100% of leaves from the fruiting zone at either 10 days after anthesis, 40 days after anthesis, or 60 days after anthesis. In the second year of the Cabernet franc study, a 15-day postveraison leaf removal treatment was also included. In both years of the Cabernet franc study, significant reductions in IBMP (range = 28 to 53%) were observed before veraison compared with the control in both 10 days after anthesis treatments (50% and 100% leaf removal). In 2007, all leaf removal treatments significantly reduced IBMP concentrations compared with the control (46 to 88%) in Cabernet franc berries at harvest, with the greatest reduction observed in the 100% leaf removal treatments at 10 days after anthesis and 40 days after anthesis. In 2008, the 100% leaf removal treatment at 10 days after anthesis and the 50 and 100% leaf removal treatments at 40 days after anthesis significantly reduced IBMP concentrations (34 to 60%) in mature Cabernet franc berries. In the Merlot trial, all leaf removal treatments significantly reduced IBMP concentrations (38 to 52%) at harvest. In summary, early season (10 to 40 day after anthesis) basal leaf removal reduced IBMP accumulation preveraison compared with the control in both studies, suggesting that early leaf removal is a more effective management strategy to reduce IBMP accumulation in grape berries than leaf removal later in the season.
... Nitrogen-containing grape-derived volatiles, 3-Alkyl-2-methoxypyrazines (MPs), are found abundantly in the stems (79.2%) rather than in the berries (20.8%) [45]. The precise biosynthesis pathway of MPs is still unclear, although they are suggested to be derived from the metabolism of amino acids [4,30]. ...
... The most important MPs, 2-methoxy-3-isobutylpyrazine (IBMP), 2-methoxy-3-secbutylpyrazine (SBMP), and 2-methoxy-3-isopropylpyrazine (IPMP), out of the seven detected in grapes, impact grassy, herbal, bell pepper, leafy, and asparagus-like odorants in several wines such as Cabernet Sauvignon, Sauvignon Blanc, Chardonnay, Cabernet franc, Carmènere, and Merlot [33,[49][50][51][52]. The most abundant among the three important MPs is IBMP, mostly found in the grape skin [4,45]. Koch et al. [53] studied the accumulation of IBMP in 29 different grapes and reported high levels of IBMP in some cultivars compared to trace levels or undetected IBMP in other cultivars. ...
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Elicitors as alternatives to agrochemicals are widely used as a sustainable farming practice. The use of elicitors in viticulture to control disease and improve phenolic compounds is widely recognized in this field. Concurrently, they also affect other secondary metabolites, such as aroma compounds. Grape and wine aroma compounds are an important quality factor that reflects nutritional information and influences consumer preference. However, the effects of elicitors on aroma compounds are diverse, as different grape varieties respond differently to treatments. Among the numerous commercialized elicitors, some have proven very effective in improving the quality of grapes and the resulting wines. This review summarizes some of the elicitors commonly used in grapevines for protection against biotic and abiotic stresses and their impact on the quality of volatile compounds. The work is intended to serve as a reference for growers for the sustainable development of high-quality grapes.
... It seems that the concentration of MPs in grapes may be the result of a balance between the biological formation and the photo-degradation of MPs throughout the ripening process. MPs might form largely in the earlier stages of grape development and photo-degradation might be greater in the ripe fruit (Allen and Lacey 1993;Roujou de Boub ee 2003;Harris, Ryona, and Sacks 2012). Thus, cool ripening conditions can lead to higher MP levels (Lacey et al. 1991;Hashizume and Samuta 1999;Marais, Hunter, and Haasbroek 1999;Hunter et al. 2004;Ryona et al. 2008) and enhance these aromas. ...
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Weather conditions throughout the year have a greater influence than other factors (such as soil and cultivars) on grapevine development and berry composition. Temperature affects gene expression and enzymatic activity of primary and secondary metabolism which determine grape ripening and wine characteristics. In the context of the climate change, temperatures will probably rise between 0.3°C and 1.7°C over the next 20 years. They are already rising and the physiology of grapevines is already changing. These modifications exert a profound shift in primary (sugar and organic acid balance) and secondary (phenolic and aromatic compounds) berry metabolisms and the resulting composition of wine. For example, some Bordeaux wines have a tendency toward reduced freshness and a modification of their ruby color. In this context it is necessary to understand the impact of higher temperatures on grape development, harvest procedures, and wine composition in order to preserve the typicity of the wines and to adapt winemaking processes.
... The intensity of the characteristic bell pepper aroma of IBMP in wine is positively correlated to factors promoting vine growth, i.e. high vigour vines usually show lower fruit exposure and a higher IBMP concentration in the fruit compared to that of less vigorous vines (Allen 2001, Wilkinson et al. 2007). Seasonal irrigation level is also positively correlated to IBMP fruit concentration, and to the intensity of the resultant bell pepper wine aroma (Roujou de Boubee 2003, Chapman et al. 2005). The amount of IBMP at harvest may be the result of a complex interaction of factors affecting vine vigour, but nitrogen fertilisation has been shown to promote IBMP accumulation, probably because of increased fruit shading (Allen 2001). ...
Background and AimsA field trial during the 2009 and 2010 seasons evaluated the impact of winter rainfall on the main compounds responsible for green aromas in grapes and wines, 3-isobutyl-2-methoxypyrazine (IBMP) and C6 compounds. These compounds are considered undesirable in grapes and wines above the threshold concentration. Methods and ResultsOne treatment subjected vines to average rainfall, while the other excluded winter rainfall by covering the ground with a plastic tarpaulin during the entire dormant season (November to mid-March). Irrigation for both treatments was maintained at a weekly rate of 70% of crop evapotranspiration until commercial harvest. Canopy growth, berry size and vine yield were significantly reduced by rainfall exclusion, and a significant increase in the fruit to pruning mass ratio was recorded from one season to another. Synthesis of IBMP was significantly greater in vines under normal rainfall, whereas C6 compounds were significantly different between treatments only at the end of the second season. Fruit and wine composition, mainly colour and mouthfeel compounds, were positively affected by the absence of rainfall in both years. Wine descriptive analysis showed that the lack of rainfall produced wines perceived as less green and of more intense fruit attributes in the first season. As a consequence of the reduction in vine growth, however, the same treatment produced wines less intense in fruit aromas and of inferior tannin quality in the following season. Conclusions These results show that the soil moisture level prior to budbreak affects both canopy growth and vine yield, even when irrigation is applied following budbreak. If the rainfall level is below normal, the positive effect on fruit and wine composition achieved through smaller berry size may be offset by a significant reduction in canopy growth, resulting in severely unbalanced vines, i.e. inadequate fruit to pruning mass ratio. Significance of the StudyGrowers aiming to minimise the level of IBMP at harvest would benefit from applying moderate deficit irrigation and nitrogen fertilisation rates and also might achieve an earlier harvest date for those vineyards where the absence of undesirable vegetal characters is considered a key harvest metric.
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Temperature, water, solar radiation, and atmospheric CO2 concentration are the main abiotic factors that are changing in the course of global warming. These abiotic factors govern the synthesis and degradation of primary (sugars, amino acids, organic acids, etc.) and secondary (phenolic and volatile flavor compounds and their precursors) metabolites directly, via the regulation of their biosynthetic pathways, or indirectly, via their effects on vine physiology and phenology. Several hundred secondary metabolites have been identified in the grape berry. Their biosynthesis and degradation have been characterized and have been shown to occur during different developmental stages of the berry. The understanding of how the different abiotic factors modulate secondary metabolism and thus berry quality is of crucial importance for breeders and growers to develop plant material and viticultural practices to maintain high-quality fruit and wine production in the context of global warming. Here, we review the main secondary metabolites of the grape berry, their biosynthesis, and how their accumulation and degradation is influenced by abiotic factors. The first part of the review provides an update on structure, biosynthesis, and degradation of phenolic compounds (flavonoids and non-flavonoids) and major aroma compounds (terpenes, thiols, methoxypyrazines, and C13 norisoprenoids). The second part gives an update on the influence of abiotic factors, such as water availability, temperature, radiation, and CO2 concentration, on berry secondary metabolism. At the end of the paper, we raise some critical questions regarding intracluster berry heterogeneity and dilution effects and how the sampling strategy can impact the outcome of studies on the grapevine berry response to abiotic factors.
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Food studies have shown that emotional responses can be influenced by food alone and by its environmental context. The influence of context on perception and liking of red wine flavors and on the emotions evoked is poorly understood. The primary aim of this research was to examine the effect of wine flavors and context by immersive environment on consumer-perceived intensities of green and floral flavors, liking, and emotions elicited during wine consumption. Red wine consumers (n = 105) tasted three Cabernet Sauvignon wines: an unaltered control wine (CW), green wine (GW; control wine spiked with 3-isobutyl-2-methoxypyrazine), and floral wine (FW; control wine spiked with rose water), in both a "floral" room (FR) and a "green" room (GR). The wine consumers were asked to taste and rate the intensity of green and floral flavors, hedonic liking, and the emotions elicited. The results showed that in both rooms, FW was rated consistently higher in floral flavor and GW was rated higher in green flavor. CW and FW were significantly (p < 0.001) more liked than the GW. Based on wine liking, three clusters were identified. CW and FW evoked significantly higher positive emotions than GW (p < 0.05), while GW evoked significantly higher negative emotions than CW and FW (p < 0.05) in both rooms. The effect of immersive environment did not influence flavor perception, hedonic liking, or emotional responses. Consumers were also separated into three clusters according to their liking of wines tasted, and despite clusters having identical liking for certain wines, the associated emotions differed.
Background and Aims: Green aroma compounds are considered undesirable when present at a high concentration in red wines. This study aimed to understand the effect of two irrigation levels and a higher than standard nitrogen fertilisation on the concentration of both 3-isobutyl-2-methoxypyrazine (IBMP) and six C6 compounds during fruit development. Methods and Results: Fruit samples were collected biweekly during the 2009 and 2010 seasons in a commercial Vitis viniferaL. Merlot vineyard in California, USA, where two irrigation levels (70 and 100% of crop evapotranspiration) and a higher than standard nitrogen fertilisation dose were implemented. The higher irrigation level and additional nitrogen promoted canopy growth and decreased fruit exposure, resulting in increased concentration of IBMP during fruit maturation. The concentration of the six measured C6 compounds, however, was not affected. Deficit irrigation increased fruit colour, quercetin glycosides and phenol-free glucose glycosides (i.e. aroma precursors), and decreased vine yield. The two irrigation levels did not differ on the sensory vegetal perception of the wines, but the additional application of nitrogen fertiliser at fruitset enhanced it. Significance of the Study: These findings confirm previous work showing that vineyard management practices influence fruit and wine concentration of IBMP, and demonstrate for the first time that the same practices have no significant impact on the concentration of six C6 compounds in grapes or on the concentration of hexanol in wines. Grapegrowers aiming to minimise IBMP concentration in fruit at harvest would probably benefit from a reduced application of water and nitrogen to the vineyard.
This review discusses the factors that affect the concentrations of methoxypyrazines (MPs) and the techniques used to analyze MPs in grapes, musts and wines. MPs are commonly studied pyrazines in food science due to their contribution of aroma and flavor to numerous vegetables such as peas and asparagus. They are described as highly odorous compounds with a very low olfactory threshold. The grape varietals that exhibit green or herbaceous aromas that are characteristic of MPs are predominantly Vitis vinifera cv. Cabernet Sauvignon and Sauvignon Blanc, but include others. The most extensively studied MPs include 3-isobutyl-2-methoxypyrazine (IBMP), 3-isopropyl-2-methoxypyrazine (IPMP), and 3-sec-butyl-2-methoxypyrazine (SBMP). It outlines the significance of methoxypyrazines in grapes, musts and wines in terms of the concentrations that are capable of contributing their sensory characteristics to wines. This review discusses methods for analyzing MPs including gas chromatography -mass spectroscopy (one or two dimension) and high-performance liquid chromatography, the appropriate extraction techniques, and the efficacy of these methods. Additionally, this review explores factors that affect pyrazine content of grapes, must and wines, such as the effects of different viticultural practices, effects of light exposure and grape maturation, climate, soil, the multi-colored Asian lady beetle (MALB) and the effects of different vinification processes.
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p style="text-align: justify;">La mise en oeuvre, sur les cépages blancs du Bordelais, d'une macération préfermentaire, provoque une modification de la composition chimique des moûts et des vins. On observe une diminution de l'acidité, une augmentation des teneurs en composés phénoliques en matières azotées, en colloïdes glucidiques et en substances aromatiques. La diffusion des composés phénoliques diffère selon les cépages, mais demeure modérée. Cette méthode de vinification qui permet d'accroître la typicité des vins blancs secs est seulement envisageable lorsque les raisins sont parfaitement sains et mûrs. +++ The use of skin contact before fermentation on white grapes from the Bordeaux area induces a change on the chemical composition of musts and wines. We have notified a decrease of acidity, an increase of the content of phenolic and aromatic compounds, an increase of proteins and polysaccharides. The diffusion of phenolic compounds depends on the variety of grape and stay moderated. This winemaking procedure, which allows to increase the typical character of the white wines, can only be used on grapes perfectly ripen and healthy.</p
Rejection of lamb carcasses due to a strong potato odor was caused by Pseudomonas taetrolens. Although of rare occurrence, this defect can be of considerable commercial concern.
ISBN 2-9500614-0-0 *INRA Station de Recherches Viticoles Ecole Nationale Superieure Agronomique Place Viala 34060 Montpellier Cedex (FRA) Diffusion du document : INRA Station de Recherches Viticoles Ecole Nationale Superieure Agronomique Place Viala 34060 Montpellier Cedex (FRA)
L'élevage des vins en barriques modifie profondément leur expression aromatique. L'étude par chromatographie en phase gazeuse et spectrométrie de masse permet d'identifier plusieurs substances volatiles appartenant à la fraction phénolique des arômes. Les vins rouges présentent naturellement une composition complexe en phénols volatils alors que celle des vins blancs est plus simple. L'élevage sous bois entraîne une augmentation notable des phénols déjà présents ainsi que l'apparition de molécules spécifiques au bois dechêne brûlé. L'interaction des levures et des bactéries avec le bois est mise en évidence. Les vins rouges se caractérisent par une présence parfois abondante d'éthyl phénols, les vins blancs qui ne subissent pas la fermentation malolactique s'en différencient par l'abondancede vinyl phénols. L'étude sensorielle de chaque substance permet de démontrer le rôle négligeable de certaines : furfural, méthyl-5-furfural, alcool furfurylique et le rôle exceptionnel joué par d'autres : cis et trans β-méthyl-γ-octalactone, vanilline et dans certains cas éthyl-4-phénol et éthyl-4-gaïacol. +++ Wood storage of wines changes profondly their aromatic expression. Several volatile substances from wines and oak woods phenolic fraction of aroma are identified by gas chromatography and mass spectrometry. Wood storage increases natural phenols concentration. Simultaneously specific burned wood molecules appear. Yeast and bacterial interaction with wood is demonstrated. Ethyl phenols are characteristic of red wines and vinyl phenols of white wines without malolactic fermentation. The sensorial analysis of each substance demonstrates the negligible intervention in wine aroma of furfural, 5-methyl-furfural, and furfuryl alcohol, and the important participation of cis and trans β-methyl-γ-octalactone, vanilin 4-ethyl-phenol and 4-ethyl gaïacol.