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The concept of berry sugar loading

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Alain Deloire at Institut Agro Montpellier
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WineLand · January · 2011
WynLand · Januarie · 2011 81
Alain Deloire
The concept of berry sugar loading
Faculty of AgriSciences, Stellenbosch University, Deloire@sun.ac.za Alain Deloire
Sugar loading – Introduction
Sugar loading can be dened as the evolution of the quantity
of sugar per berry, expressed as mg per berry, from véraison
onwards. Véraison corresponds to the onset of fruit maturation.
In the grapevine, this fruit maturation starts with an abrupt
softening of the berry (within 24 hours), which then becomes
transparent. This softening goes hand in hand with sugars being
actively introduced into the berry (sucrose rapidly hydrolysed
into hexoses: glucose and fructose). In red and black cultivars,
véraison is characterised, after softening, by skin colouring as a
result of the biosynthesis of anthocyanins.
The evolution of sugar loading in grape berries gives an
indication of the ripening process from a new perspective
and is a novel approach to identifying practical indicators for
obtaining particular styles of grapes and wine. Sugar loading
may also provide information on ripening kinetics and enables
the principal phases of ripening to be distinguished (McCarthy &
Coombe, 1999; Wang et al., 2003a & b; Hunter & Deloire, 2005).
Furthermore, this information provides a greater understanding
of how grape quality develops in the vineyard.
Sugar loading calculation
Phloem sugar transport, principally to the esh cells, has been
characterised in studies on plant-to-berry sugar loading, and
phloem sugar unloading, notably by the peripheral vascular
system of the berry (Ollat & Gaudillère, 1996; Fillon, 1997; Hunter
& Ruffner, 2001; Wang et al., 2003a). Phloem sugar unloading
into cell vacuoles occurs mainly via an apoplastic mechanism,
which requires the intervention of hexose transporters (Agoerges
et al., 1995; Terrier et al., 2005). From above-mentioned
studies, it can be concluded that sugar loading into the berry,
coupled with the dynamics of sugar concentration changes,
may be considered a useful indicator of grape quality. It takes
into account the evolution of the sugar level per berry (mg per
berry) and therefore enables the kinetics of sugar concentration
changes to be monitored.
Kinetic monitoring of the quantity of sugar per berry may be
considered as a method of measuring the plant’s physiological
functioning (Hunter & Deloire, 2005; Deloire et al., 2004; Wang
et al., 2003b; Carbonneau & Deloire, 2001; Carbonneau et
al., 1998) and in particular, photosynthesis, which is a reliable
indicator of temperatures to which the vine is subjected under
given conditions over a specic time period and grapevine water
status.
Active sugar loading is calculated on the basis of berry volume
(or berry fresh mass) and sugar concentration (McCarthy &
Coombe, 1999; Brenon et al., 2005; Hunter & Deloire, 2005).
Example of sugar loading calculation
For a berry with a ripeness level of 25 °brix:
Convert 25 °brix to in probable alcohol:1.
25 x 0.59 = 14.75° in probable alcohol, where 0.59 is ·
the coefcient used for yeast activity to convert brix in
probable alcohol (this coefcient as to be adapted to
the probable alcohol level).
Determine mg of sugar per ml probable alcohol:2.
To obtain 1° probable alcohol, 17 g/L of sugar is required.
14.75° x 17 g/L = 250.75 g/L, which is equivalent to ·
250 mg of sugar per ml (in this example).
Calculate quantity of sugar per berry:3.
In addition to measuring °brix, the volume of a berry (or
berry fresh mass thereof) should also be measured so
that the quantity of sugar per berry can be calculated.
Approximately 50 berries should be used to determine
berry fresh mass so that the single berry fresh mass is an
average of a berry population.
250 mg x volume of a berry (or the berry fresh mass ·
thereof, because for many varieties there is a linear
correlation between berry volume and fresh mass).
It should be taken into consideration that this calculation is
only an approximation of sugar loading into berries. This is due
to a number of reasons; amongst others seed volume, sugar
distribution between skin and pulp. Despite the calculation being
an approximation, with associated shortcomings, it nevertheless
is a useful indicator and the use thereof is becoming increasingly
more common.
Profiles of sugar loading
It is possible to distinguish three principal sugar loading pro-
les:
Continual and rapid loading1.
This type of sugar loading occurs from véraison and is related
to the active functioning of carbon production sources (leaves)
which supply plant sinks (berries, secondary shoots etc.) du-
ring their growth phases. It is therefore often associated with
signicant vegetative growth and greater berry volume. Phenolic
maturity is not affected. This type of loading is often considered
benecial for the production of rosé, fresh fruit red wines, or
pleasant aromatic white wines.
Slow sugar loading – inhibition of ripening2.
Low sugar content per berry, associated with a slow loading
rate, can be considered to “blocked” ripening and this could
be indicative of an imbalance in the vine. If major physiological
problems, such as mineral deciencies, viral diseases etc., are
WineLand · January · 2011
82
WynLand · Januarie · 2011
excluded, blocked ripening can often be related to excessive
water decit (Wang et al., 2003b) or to an excessive crop load
in relation to the exposed leaf surface (Carbonneau & Deloire,
2001).
In all grape varieties, this type of situation is far from ideal in
terms of the standard vinication practices in white and dry red
wine production. Furthermore, in relation to red and black gra-
pes, this situation may be associated with blocked technologi-
cal and phenolic maturities. Ultimately, it may be necessary to
adapt the fermentation procedure to this type of grape, with
thermo vinication and short macerations with limited extraction
being the preferred options.
Sugar loading presenting a plateau phase3.
Vines showing this tendency present a phase of active sugar
ripening ripeness overripeness
sugar per berry (mg/berry)
•The plateau is reached when the speed
of sugar loading is 3 mg/berry/day.
The Brix value at the beginning of the plateau
is an important criteria.
day « 0 »
Slope = the speed
of sugar loading
(mg/berry/day)
Duration of the plateau
(number of days after day «0»)
= allows to determine the level
of ripeness from fresh to mature fruit
for the red cultivars.
ripening ripeness overripeness
sugar per berry (mg/berry)
•The plateau is reached when the speed
of sugar loading is 3 mg/berry/day.
The Brix value at the beginning of the plateau
is an important criteria.
day « 0 »
Slope = the speed
of sugar loading
(mg/berry/day)
Duration of the plateau
(number of days after day «0»)
= allows to determine the level
of ripeness from fresh to mature fruit
for the red cultivars.
FIGURE 1. Berry sugar loading concept. This theoretical curve is based on data obtained over five years using at least 20 different grape varieties in different countries, principally
France, Spain, Argentina and Chile. This curve has been recently calibrated for some South African viticulture areas and cultivars (in collaboration with Distell).
loading in the berry (ripening), followed by a plateau represent-
ing a cessation of sugar loading and corresponding to matu-
rity (Hunter & Deloire, 2005; Deloire et al., 2005a & b). In some
cases, there is a third phase corresponding to a possible de-
crease of the quantity of sugar per berry (over ripening). To date
a probable explanation for the occurrence of this phase has not
been identied.
Theoretical berry sugar loading curves (evolution of berry sugar
content over time) are presented in Fig. 1. These curves are
based on data obtained over ve years using at least 20 differ-
ent grape varieties in mainly France, Spain, Argentina, Chile and
recently in South Africa.
The implications of this curve in terms of dening the nished
wine is important: depending on whether grapes are harvested
in the early, mid or later stages of the plateau phase, the wine
FIGURE 2. The Berry Aromatic Sequence (B.A.S.): Sugar loading and style of wine. Example of relationships between the berry sugar loading curve and the possible related style
of wine, for Cabernet-Sauvignon. After “day 0”, three successive main periods have been determined: a fresh fruit period, a “neutral” period and a mature fruit period. In terms of
harvesting dates, these periods have been determined according to the number of days after “day 0”, which corresponds to the sugar loading “plateau”, and not directly to a calendar
date. This introduces the concept of “physiological clock”.
WineLand · January · 2011
WynLand · Januarie · 2011 83
will be characterised by fresh fruit, neutral-spicy or mature fruit
avours, respectively.
The concept of Berry Aromatic Sequence (B.A.S.)
The above curve demonstrates that selecting a harvesting date
according to the quantity of sugar per berry in conjunction with
other indicators (titratable acidity, malic and tartaric acids, pH,
berry volume, berry tasting, tannins, anthocyanins, etc.) ena-
bles different styles of wine to be produced. Hence, for a ba-
lanced red wine, complete ripeness will be achieved between
one and ve weeks after the cessation of sugar loading (Fig.
2). Once the plateau phase of berry sugar loading has been
reached, the evolution of ripening will depend on other factors
such as cultivar, bunch microclimate, the leaf/fruit balance, the
ratio of primary to secondary shoots and the climate mainly du-
ring berry ripening (maximum temperature, night-time coolness,
sea-breeze, wind-speed, late season rains, and various factors
which are quantiable) (Bonnardot et al., 2005; Carey, 2001;
Hunter & Bonnardot, 2002).
It should be noted that the plateau phase in sugar loading may
be reached at different sugar concentrations (brix), depending
on the cultivar and environmental conditions. A red cultivar, with
a very high sugar concentration (brix) when the maturity plateau
is reached, will not always be desirable for the production of
certain types and/or styles of wine (Deloire et al., 2008).
Monitoring ripening with various indicators, coupled with appro-
priate analytical data measurements such as berry fresh mass
or volume, brix, sugar loading, evolution of titrable acidity, malic
acid tartaric acid, pH, colour evolution, anthocyanins, tannins,
berry tasting, etc.) enable decision-makers to determine the
optimum harvesting date, a major consideration in determining
grape quality. Such monitoring provides a greater understand-
ing of vine morphological and physiological parameters dur-
ing ripening and therefore vineyard practices can be adapted
to production objectives. There are, in most vineyards, several
potential optimal harvesting dates and optimal ripening levels
according to the desired style of wine. The wine is therefore cre-
ated in the vineyard!
As the world becomes more technologically advanced, more
advanced technology is being developed to monitor berry rip-
ening. This technology is rapidly being adopted by large estates
and co-operatives to enhance their marketing edge.
Acknowledgements
Many thanks to Vivelys and Nicolas Bernard (Montpellier,
France) for providing the data on berry sugar loading. Many
thanks as well to Dr Mary Kelly (Montpellier 1, France) and to
Carolyn Howell (ARC Infruitec-Nietvoorbij) for helping with the
English translation.
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Article
  • Apr 2022
  • SCI HORTIC-AMSTERDAM
Late pruning is a field technique that has recently been proposed to mitigate the advance in phenology produced by global warming. However, contrasting effects have been observed depending on the cultivar and the date of pruning evaluated. In this work, our aim was to evaluate the effects of delayed pruning on phenology, vegetative growth, yield components, and crop evapotranspiration in cv. Malbec. During three seasons, winter pruning (WP) was compared to three late pruning treatments: plants pruned at budburst (BB), at 2-3 unfolded leaves (2-3 L) and at 8 unfolded leaves (8 L). Our results showed that late pruning treatments delayed phenology from budburst to veraison the three years of experiment, but harvest date could not be postponed. Plants pruned at 2-3 L and 8 L showed a decrease in vine yield of 17% and 60%, respectively while plants pruned at budburst showed the same yield than control vines. Late pruning treatments did not cause carry over effects on yield formation the following season. Finally, plants pruned at 2-3 L and 8 L reduced annual crop evapotranspiration by 5–10% mainly at the beginning of the cycle, compared to control and BB. Our study provides evidence that late pruning is effective to delay the first phenological stages but it is not as effective to delay the total soluble solids accumulation fixed for harvest, in our conditions.
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... During phase II of the experiment, all treatments were harvested on different dates but at a similar average ripeness level of 22 °Brix ( Figure 2B). Berries were thus sampled at the end of the main sugar accumulation period before any major weight loss to avoid adding another variable in the experiment (Deloire, 2011). As observed in , phloroglucinolysis conversion yields can significantly vary between extraction solvents. ...
Effect of high and extreme high temperatures on berry tannin composition in Vitis vinifera cv. Shiraz
Thesis
Full-text available
  • Aug 2021
Climate change is leading to an increase in average temperature and in the frequency and severity of heatwaves, and is already significantly affecting grapevine phenology and berry composition. As weather conditions of Australian warm and hot grape growing regions evolve, flavonoids, for which biosynthesis depends on bunch microclimate, are expected to be affected. These compounds include flavan-3-ols and tannins which are important contributors to grape and wine quality. The aim of this project was to determine if berry tannin accumulation is sensitive to high temperature. While the synergistic effect of light and temperature on anthocyanins has been intensively examined, more knowledge is required for tannins as their metabolic pathway is yet to be fully elucidated, and their structural analysis is limited due to their complex nature. Using a multi-disciplinary approach, the research focused on how high (>35 °C) and extreme high (>45 °C) temperatures impact on berry physiology, survival and detailed tannin composition. Temperature-related parameters (duration, intensity, day/night, phenological stages, levels and berry acclimation) were investigated across four glasshouse experiments, conducted on well-irrigated potted Shiraz grapevines. Bunch or whole-vine temperature was manipulated using experimental systems that prevented differences in canopy/bunch light exposure while allowing natural light and UV. The first two experiments used a factorial design to either investigate the effect of a single or several whole-vine heat treatments (+6 °C) or to assess the influence of high day (+8 °C; 45 °C) and night (+6 °C; 33 °C) bunch temperature, during berry development. Another experiment examined different intensities (35-54 °C) and durations (3-39 h) at mid-ripening (E-L 36). The last experiment combined the previous parameters that had affected tannins. Two additional assays evaluated the potential temperature impact on subsequent wine composition using wine-like extraction and micro-scale winemaking. Detailed tannin composition was primarily determined by liquid chromatography-tandem mass spectrometry after phloroglucinolysis, with complementary total tannin concentration (methyl cellulose precipitable assay). Tannin size distribution (gel permeation chromatography), together with primary and secondary metabolites (gas and liquid chromatography-mass spectrometry) were also analysed on key samples to provide a more comprehensive picture. Providing berries were not damaged, tannin accumulation experienced just a short delay following high temperature exposure during early berry development. Differences were likely due to a combination of berry development disruption as well as a deregulation of some genes involved in tannin biosynthesis. Parameters most commonly impacted across all experiments were seed tannin size (increased) followed by tannin content (decreased) and skin galloylation (increased). Most differences were no longer evident by harvest, but if any, extractability was increased compensating for the decrease in berry phenolics. To complement compositional responses, berry survival thresholds were identified with green berries exhibiting visual damage for temperatures above 42-44 °C while red berries only started to necrose above 50 °C. In damaged berries, skin tannins were dramatically reduced while seed tannins were mostly preserved. With the experimental system used for this thesis, tannin accumulation showed an elastic response to high temperature and if berries were not shrivelled, quality was not impaired at harvest by the sole effect of temperature. The project provided enhanced knowledge on upper temperature limits for viable wine production, in turn informing critical timing for mitigation strategies.
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Vine and water a short review
Article
Full-text available
  • Mar 2004
  • J INT SCI VIGNE VIN
Water is an important factor in the terroirs of grape-growing regions. The vine obtains water from rainfall and the water table and when it is in short supply, it is necessary either to irrigate or accept the effects of water stress. Depending on the intensity of the water stress and the period at which it occurs, it may or not be favourable for the harvest and the wine it is used to produce. The objective of this article is to provide some information on the relationship that exists between the vine and water. The climate and the soil, which are essential but not the sole elements of this relationship will only be touched upon, but we will discuss in a non exhaustive way, with information's from the bibliography or from our research, the following aspects: the root system, vegetative growth, the relationship between plant architecture and the water status of the vine, the carbon balance and the biochemical composition of the grape berry in relation to vine water status. We will also present the currently available techniques for measuring vine water status and its evolution during the vegetative cycle as a function of water reserves in the soil easy to use by the roots. Finally examples are presented of possible recommendations for vine cultural practices as a function of the vine water status evolution during the growth, according to the predawn leaf water potential thresholds.
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Study of sugar phloem unloading in ripening grape berries under water stress conditions
Article
Full-text available
  • Oct 2003
  • J INT SCI VIGNE VIN
Sugar phloem unloading in ripening grape berries (Vitis vinifera L. cv. Syrah) was studied under water stress conditions using the «berry- cup» technique. After veraison, berry growth, the potential Exposed Leaf Area (pELA) and photosynthetic activity are clearly reduced in water-stressed vines (-0.5 ≥ Ψb ≥ - 0.6 MPa) as compared to normally-watered vines (Ψb ≈ = -0.2 MPa). The ratio pELA/yield is also reduced, which is particular to this experiment. The berries' ripening period (between veraison and maturity) can be divided into three growth phases, IIIa, IIIb and IIIc. During phase IIIa, the berries grow rapidly; at this point, water stress severely inhibits cell expansion of the berries but does not impact on daily sugar accumulation. During phase IIIb, the berries grow slowly in both water-stressed and control vines. Water stress can shorten this phase and reduce sugar accumulation in the berries by decreasing daily sugar unloading. During phase IIIc, the fresh weight and volume of the berries decreases as does the daily sugar unloading. During the day, sugar unloading in ripening berries occurs mainly in the morning (7 am to 10.30 am) and at noon (1 to 1.30 pm); little sugar is unloaded in the afternoon (4 pm to 4.30 pm). Moderate water stress from veraison to maturity affects vegetative growth (i.e. the growth of primary and secondary shoots), and reduces the exposed leaf area, photosynthetic activity, berry growth, and the accumulation of sugar at the end of ripening (phases IIIb and IIIc).
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Assimilate transport in grapevines - Effect of phloem disruption
Article
Full-text available
Assimilate translocation in mature grapevines (cv. Gewürztraminer and cv. Harslevelü) under field conditions was investigated during the growth season by quantifying individual sugars and organic acids in mature leaves, shoot bark and berries, as affected by girdling the shoot just above the bunches. Tissue was sampled at berry set, pea size, veraison and ripeness stages of the vine. Invertase activity was determined in the shoot bark at ripeness. In the leaves, malic acid concentrations reached lowest levels at pea size, but increased thereafter. Tartaric acid decreased after peaking at pea size stage. Tartaric acid concentrations increased with girdling. Despite the increase in leaf age, sucrose concentrations remained virtually stable during the season, emphasising the importance of mature leaves for nourishing bunches. Girdling resulted in a build-up of sucrose in the leaves. In the bark, malic and tartaric acid stayed more or less the same during the growth period, but increased above the girdle. As a result of phloem disruption, sucrose also increased. The increase in glucose and tartaric acid is believed to result from catabolic cleavage of sucrose by invertase. Invertase activity was evident in the bark (of mature Harslevelü vines) at ripeness, which may indicate involvement in osmotic adjustments and gradients in the bark/phloem structure. In the berries, malic and tartaric acids reached peak concentrations at pea size. The volume increase during the ripening period, and in the case of malic acid also respiratory loss, resulted in a decrease in organic acid concentration. Malic acid continued to decrease after the initial decline, whereas tartaric acid stayed virtually stable. Girdling had no marked effect on organic acid accumulation in the berries. Sucrose concentrations were low during the first part of the season, but increased thereafter. Sucrose concentrations during ripening increased with girdling, which may represent a concentration effect and/or import from the rest of the vine. Sucrose concentrations (in mature Harslevelü vines) were indeed lower below than above the girdle. Comparison of sucrose concentrations in the leaves, bark and berries showed the existence of a decreasing concentration gradient, in line with the source:sink transport concept. An equally prominent decrease in sucrose:glucose ratio in the berries from the start of the ripening period indicates that vacuolar integrity (compartmentation) was affected in the ripening berry, most probably allowing hydrolysis of sucrose by invertase and decreasing osmotic potential within the berry. The results provide further evidence for the hypothesis of an osmotic gradient driven transport to the berry.
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An in vivo Experimental System to Study Sugar Phloem Unloading in Ripening Grape Berries During Water Deficiency Stress
Article
Full-text available
  • Nov 2003
An in vivo experimental system-called the 'berry-cup' technique-was developed to study sugar phloem unloading and the accumulation of sugar in ripening grape berries. The berry-cup system consists of a single peeled grape berry immersed in a buffer solution in a cup prepared from a polypropylene syringe. A small cross-incision (2 mm in length) is made on the stylar remnant of a berry during its ripening phase, the skin of the berry then being easily peeled off, exposing the dorsal vascular bundles without damaging either these or the pulp tissue of the berry. The sites of sugar phloem unloading are thus made directly accessible and may be regulated by the buffer solution. In addition, the unloaded photoassimilates are easily transported into the buffer solution in the berry-cup. With the berry-cup technique, it takes 60 min to purge the sugar already present in the apoplast, after which the amount of sugar in the buffer solution is a direct measure of the sugar unloading from the grape berry phloem. The optimum times for sampling were 20 or 30 min, depending on the type of experiment. Sugar phloem unloading was significantly inhibited by the inclusion of either 7.5 mm NaF or 2.5 mm PCMB in the buffer solution. This study indicates that sugar phloem unloading in ripening grape berries is via the apoplastic network and that the process requires the input of energy. The system was shown to be an appropriate experimental system with which to study sugar phloem unloading in ripening grape berries, and was applied successfully to the study of berry sugar unloaded from grapevines subjected to water stress. The results showed that water deficiency inhibits sugar unloading in grape berries.
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BONNARDOT, V., PLANCHON, O., CAUTENET, S. (2005) : The sea breeze development under an offshore synoptic wind in the South Western Cape and implications over the Stellenbosch wine-producing area. Theoretical and Applied Climatology, 81 (3-4), 203-218.
Article
  • Jul 2005
Sea breezes were investigated during the maturation period of wine grapes in the South-Western Cape under particular synoptic wind conditions (onshore for Table Bay and offshore for False Bay). Observations from an automatic weather station network located in the Stellenbosch wine-producing area as well as the Regional Atmospheric Modelling System (RAMS, non-hydrostatic, parallel, version 4.3) were used. Results showed that two sea breezes developed, one from Table Bay late in the morning, and the other from False Bay later in the afternoon. The coastal low strengthened and deflected the sea breeze from Table Bay towards the south and south-east of the study area, while the offshore large-scale circulation hindered the development of the sea breeze in the opposite direction over False Bay and delayed its movement towards land. The decrease in temperature resulting from the onset of the sea breeze from the Atlantic early in the afternoon could be significant for viticulture, reducing the duration and intensity of high temperature stress on grapevine functioning at the coolest locations.
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Investigation of assimilate import mechanisms in berries of Vitis Vinifera var. 'cabernet sauvignon'
Article
  • Dec 1996
Carbon and water balance, as well as mineral nutrient import was investigated in grape berries throughout their development on fruit-bearing cuttings. During the first growth period, carbon was equally partitioned between pericarp, seed development and respiration. Water was mainly imported by xylcm. At the onset of ripening, carbon import increased five times. A stimulation of water flow from phloem was sufficient to explain this higher rate of carbon imports. Mineral nutrient accumulation was also related to the pathways of water import. Calcium was imported during the first growth period and potassium mainly during ripening. Our data support the hypothesis that the sink strength of a grape berry increases substantially at the onset of ripening, and that the controlling parameters of phloem transport are also modified at this stage.
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Is weight loss in ripening grape berries cv. Shiraz caused by impeded phloem transport?
Article
Berry shrinkage in ripening grapes cv. Shiraz is systemic within a given grapevine and coincident between grapevines in any given season. In this present study on weight loss in ripening berries, ripening curves of non-solutes per berry (largely water) were similar to curves for berry weight (as a function of time). Both sets of curves were equivalent with respect to timing of maximum weights and subsequent rates of weight loss. However, curves of solutes per berry (largely sugar) increased steeply up to the time of maximum berry weight, then slowed and plateau-ed. We suggest that phloem sap is the sole source for water and solutes that enter grape berries subsequent to veraison, and accumulate until maximum berry weight. We further suggest that phloem flow becomes impeded at maximum berry weight. As berry ripening proceeds, continuation of berry transpiration leads to berry shrinkage and a concentration of solutes; i.e. any increase in juice Brix depends on shrinkage. One implication is that assimilates enter a berry up to the onset of shrinkage, whereafter accumulation of non-anthocyanin glycosides (including glycosides of flavour compounds) depends upon their synthesis in situ.
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