Grape Berry Development and Ripening

Grape berries exhibit a double sigmoid growth pattern.

The First Growth Phase:

• occurs from flowering to approximately 60 days post flowering
• growth occurs mainly by cell division causing the berry to expand
• tartaric and malic acids are the most prevalently accumulated compounds during the first growth phase
• tartaric acid is accumulated during the initial phase it's concentration is highest in the periphery of the grape berry
• malic acid is accumulated in the flesh cells at the end of the first growth phase
• hydroxycinnamic acids accumulate in the flesh and skin of the berry
• tannins, including the monomeric catechins, accumulate in the skin and seed tissues but nearly absent in the flesh

Lag Phase:

• the length of the lag phase is specific to the variety
• the end of the lag phase corresponds to the end of the herbaceous phase of the fruit

Second Growth Phase or Ripening

• berries switch from a status where they are small, hard and acidic, with little sugar to a status where they are larger, softer, sweeter, less acidic, and strongly flavoured and coloured
• ripening phase begins in August in the north hemisphere and lasts about 45 days, depending on the environmental conditions
• the berry approximately doubles in size between véraison and harvest
• the solutes accumulated in the grape berry during the first period of development remain at harvest; but due to the increase in berry volume, their concentration is significantly reduced
• malic acid is metabolized and used as an energy source during the ripening phase
• tannins also decline considerably on a per-berry basis after véraison
• lthough the first growth period contributes to the final quality of the berry, the most important event occurring during the second growth period is a massive increase in compounds, the major ones being glucose and fructose, as a result of a total biochemical shift into fruit ripening mode

References:
1. Text and berry illustration from: Carlos Conde, Paulo Silva, Natacha Fontes, Alberto C. P. Dias, Rui M. Tavares, Maria J. Sousa, Alice Agasse, Serge Delrot, Hernâni Gerós, Biochemical changes throughout Grape Berry development and fruit and wine quality, Food, 1(1), 1-22 ©2007 Global Science Books.
2. Illustration of the double sigmoid curve from: Moschou, Panagiotis & Aziz, Aziz & Roubelakis-Angelakis, Kalliopi, Chapter 7, Polyamines and grape berry development, The Biochemistry of the Grape Berry, (2012), 137-159.

Grape Health During a Heat Wave

We have been having an unusally hot summer, punctuated by heavy rainfall. We have been seeing some signs of berry stress in our Chenin Blanc where the berries in some clusters have been raisining. Here is a minor example of what we are seeing. I am bringing my tweezers to the vineyard so that I can clean these sunburnt grapes from the cluster.

I was telling my husband about what I was seeing and then I came across an article in Wine Industry Network, written by Mark Greenspan called "Growing High Quality White Wine Grapes".¹ It was a timely article to be reading because we are now in the lag phase of berry growth and experiencing high heat bordering on drought conditions and his article was focussed on this phase of berry growth.
White wine grape growing is more difficult than red wine grape growing. A white grape is inherently more vulnerable to degradation since it doesn’t have an arsenal of polyphenols protecting it which is the case in red grapes because they have anthocyanin compounds for protection.
However, a white grape does have some means of protection which can generate aromatic compounds if the stress event occurs during the grape lag phase.
Benefits of heat stress during grape lag phase:

• aromatic compounds are produced in abundance during periods of abiotic stress, such as a heat wave, because they help protect the plant from oxidation
• water stress imposed during lag phase upregulates the synthesis of many secondary metabolites associated with better color and mouthfeel
• other compounds associated with water stress imposed pre-veraison include thiols or mercaptans, organic compounds containing sulfur that are associated with passion fruit, guava, and grapefruit aromas and flavors
• Glutathione is an important compound in helping white grapes with stress
  
• glutathione is synthesized in many plants in response to abiotic stress such as drought, this compound breaks down into thiols, which accounts for the many desirable aromatic compounds in wine
• glutathione is integral in protecting plant tissue from oxidative stress, which is more important in white grapes given that the antioxidant anthocyanin is lacking
• biochemical pathways responsible for terpenes and 13-norisprenoids (derived from carotenoids) are upregulated by water stress between lag phase and veraison, these are the compounds associated with floral and earthy aromas

The link between phenolics and water stress is well-established. In places where irrigation is practiced, such as California, farming practices can be manipulated to increase the tannins and color by planning the appropriate time to irrigate after hot weather.
This article recommended that excessive leaf removal be avoided. Where severe heat events are on the rise, shade cloth and microsprinklers are being used to cool the fruiting zone.
My husband and I are quite conservative when it comes to leaf pulling. My husband is of the mindset that the leaves on the west side of the canopy should be left in place in order to protect the grapes from the heat of the afternoon sun. Currently, we are working in our Chenin Blanc, hedging, shoot thinning, shoot tucking, shoot positioning, and leaf pulling. This is what the canopy looks like on the left side and how the leaf pulled grapes look like on the right side of the photo.

We are trying to strike a balance between air flow, which is critical for maintaiining a clean canopy and grapes and preventing the grapes from getting too much sun so that they do not raisin before veraison.
The weather for the first few days in August shows no rain, but also thankfully, no temperature hitting 90 degrees!
References:
1. Mark Greenspan, Wine Industry Network, "Growing High Quality White Wine Grapes.

Two Stages of Grape Berry Development

Our friend has been helping us with our vineyard work. Recently, we showed him the Chardonnay fruitset 2 weeks after bloom. He was surprised at how large they were and so was I. He said that at this rate, the grape bunch will be huge.

Grapes, however undergo a lag phase between two growth phases. Sneaky berries!
Here is a chart showing all that is going on once berries are set. The chart illustrates the double sigmoidal curve of berry growth and development:¹

Development During First Growth Period2

Development During Second Growth Period

The first period of growth lasts approximately 60 days past bloom The berry is formed and the seed embryos are produced Rapid cell division in the pericarp occurs through the first few weeks, establishing the total number of cells within the berry The berry expands in volume as solutes such as tartaric and malic acid accumulate Tartaric acid appears to accumulate during the initial stages of berry development, and malic acid accumulates just prior to véraison Hydroxycinnamic acid also accumulates during the initial period of growth Tannins including the monomeric catechins also accumulate during the first period of growth Minerals, amino acids, micronutrients, and aroma compounds (such as methoxypyrazines have all been observed during the first period of berry growth

The first growth period is followed by a lag phase during which little or no growth occurs. The second growth phase coincides with the onset of ripening (veraison) Cells in the pericarp undergo expansion The berry expands in size due to the influx of water, carbon and mineral nutrients Softening and coloring of the berry occurs during ripening Synthesis and accumulation of anthocyanins occur during ripening There is an increase in abscisic acid (ABA), sugar levels and color development The big change during the second growth period is the accumulation of glucose and fructose as the grape shifts into ripening mode Important aroma and flavor compounds are produced late in fruit ripening The berry approximately doubles in size between the start of ripening and harvest

It is important to understand the development of the grape berry because knowing when flowering occurs, the lag phase can be predicted. In our case, if flowering occurred during late June, our lag phase will be toward the end of August. Our nets should be up by that time to prevent the birds from eating the fruits of our labor!

References:
1. Moschou, Panagiotis & Aziz, Aziz & Roubelakis-Angelakis, Kalliopi, Chapter 7, Polyamines and grape berry development, The Biochemistry of the Grape Berry, (2012), 137-159.
2. James Kennedy, Understanding Grape Berry Development, Practical Winery and Vineyard Journal, July/August 2002.

Berry Shriveling in our Chenin Blanc

We are now up close and personal with our Chenin Blanc as we shoot tuck and move the netting into the proper trellis slot for deployment. Before the hurricane-AKA-tropical storm Ida came, our Chenin Blanc berries were green and hard indicating that they had not yet left the lag phase of development. After the storm, the berries were beginning to soften and are now in the ripening phase, véraison.
We have been noticing, even during the lag phase that our Chenin Blanc looked like this:

We thought that it might be sunburn and by searching the Internet, we came across an article written by American Vineyard called Preventing Sunburn on Grapes. What drew me to this article was this photo:¹

It certainly looked like what we were seeing in the Chenin Blanc so I read on. Sunburn can happen during any stage of fruit development if the conditions are right which include too much sun, not enough shade and low humidity. The bunch may be soft at first, but after a period of time, the affected area dries up and creates a berry that is hard on one side and partially mummified.
Here is an example from our Chenin Blanc:

The advice on these sunburned grapes is to drop them.
More recommendations from the article include:

• Leaf pull between bloom and véraison
• Early leaf removal prevents the grapes from sudden exposure to strong sunlight late in the season
• Leaf removal should involve only 2-4 leaves on each shoot
• Skip leaf removal if vines lack strong vigor
• If possible, drape a shade cloth over the fruit to decrease the amount of direct sunlight

Their advice for long term strategy include:

• Orient the vineyard rows in a north-south direction
• Provide adequate nutrients (especially nitrogen, phosphorus, and potassium) to the plants, to support strong canopy growth
• Vines can be watered using overhead irrigation like a sprinkler or hose during periods of hot temperatures to create an “evaporative cooling” effect

References:
1. American Vineyard, Preventing Sunburn on Grapes, July 24, 2020.

Vintage 2020: Next Steps for the Cabernet Sauvignon and Cabernet Franc

We left the Cabernet Sauvignon and the Cabernet Franc in their half ton bins at the Jonathan Edwards Winery undergoing a "cold" maceration until Sunday, October 25, 2020 when we went back to inoculate the must. Jonathan Edwards was harvesting his Cabernet Franc at this time so we were able to repay his kindness by helping to harvest his grapes. Around 1 p.m. we rehydrated our yeast, F15 for the Cabernet Sauvignon and FX10 for the Cabernet Franc.

We calculated that we might have at most 80 gallons of juice. The yeasts that we had chosen came in convenient 80 gram packets so the two yeasts, F15 for the Cabernet Sauvignon and FX10 for the Cabernet Franc were rehydrated in 800 mL of water at 100 degrees. The F15 seemed a little bit more reluctant to be rehydrated and the FX10 was faster at rehydrating and "blooming". The must for each of the two varieties was at a very hospitable 62 degrees Fahrenheit so after the 20 minute rehydration, the 800 mL of must was added in two aliquots each spaced 10 minutes apart. A little after 2 p.m. both bins were inoculated with their respective yeasts and covered with a special half ton bin covering that my husband (Procurement Officer) purchased.

Beginning on October 26 we went to Jonathan Edwards Winery three times a day to do punch downs. During this time, the yeasts were in their lag phase, beginning to get accustomed to their grapey environment. What we did see was that the weather was going to turn decidedly cold on Friday so on Tuesday evening, my husband purchased a small rotating heater to help the yeasts along. We set up the heater on Wednesday morning, October 28, 2020:

After the heater was put in place the yeast began their activity of converting sugar into alcohol. We monitored this by the change in Brix that we observed:

Variety	10/19	10/25	10/27	10/28	10/29	10/30	10/31	11/1	11/2
Cabernet Sauvignon Brix	22.4	20.5	20.5	19	16.6	15	13.5	12.2	10.6
Cabernet Franc Brix	23.5	23.2	21.0	19.5	18	15.5	14	12	10.4

After the heater was put in place, the yeasts came out of their lag phase and entered their rapid division phase and the decrease in Brix attest to this. It is still a slow fermentation so we hope to capture some nice aromatics in the process.

2024 Chenin Blanc and SAD: Part Two

Recently, I blogged about 2024 Chenin Blanc and SAD: Part One. This post is a continuation with the goal of trying to figure out what causes impaired sugar import into the grape berries. Sugar accumulation disorder (SAD) and suppression of uniform ripening (SOUR) are both classified as grape ripening disorders.
In order to understand why SAD and SOUR can occur in grapes, we have to go back to how grapes ripen since these disorders occur shortly after the onset of ripening. After fruitset and the first growth stage, the grapes enter into a lag phase before véraison. This progression of first growth, lag phase and véraison in grapes is characterized by a double-sigmoid curve, which is best summarized by this graphic:

For additional information about grape berry ripening, please check out this post: Grape Berry Development - Heading into Véraison.
Ripening involves higher levels of abscisic acid (ABA), brassinosteroids, and ethylene. Grapes affected with SAD or SOUR exhibit the following symptoms:

• Grape berries look deflated
• Reduced berry weight, symptoms appear shortly after onset of ripening
• Low (10–13 °Brix) due to arrested phloem influx
• Titratable acids often high due to berry dehydration
• Tartaric and malic acid content per berry not changed; oxalic and citric acid reduced
• Most amino acids reduced; higher hydroxyproline, arginine, and alanine
• Low yeast-assimilable N, K+, and other nutrients; low K+ in rachis and pedicels
• Low anthocyanins, genes for biosynthesis delayed; elevated skin tannins
• Rachis and pedicels are green and show no symptoms

Here are pictures of unripe Chenin blanc that we dropped prior to our harvest. Many of the grapes did have low °Brix that we checked for using our hand held refractometer or by taste test. The rachis and the pedicels did appear green so that did not help us in the culling but in the process of dropping nearly one ton of grapes, we were able to hone in on which bunches were likely to be affected with SAD and SOUR.

Next blogpost will be on the possible causes of SAD and SOUR mentioned in the review.
References:
1. Griesser M, Savoi S, Bondada B, Forneck A, Keller M. Berry shrivel in grapevine: a review considering multiple approaches. J Exp Bot. 2024 Apr 15;75(8):2196-2213. doi: 10.1093/jxb/erae001. PMID: 38174592; PMCID: PMC11016843.

Chardonnay Fermentation Experiments

Our harvest of the Chardonnay occurred on September 28, 2019. Since we had such a small amount of grapes, we were able to handle this fermentation in our basement and our friends helped us to extract the juice by stomping on the grapes. The juice went by gravity flow into our basement into the waiting stainless steel kegs where the first step was the cold settling of the larger pulp matter.
We harvested about 290 pounds of Chardonnay, which turned out to be approximately 26 gallons of juice, enough to try three small experiments on fermentation with different yeasts. We chose X16, CH9 and D47 for the fermentations. Our goal is to see if there is an organoleptic difference imparted by the different yeasts on the resulting Chardonnay wines.

Here is what we know from the product data sheet of X16, CH9 and D47:

Yeast Strain	Fermentation Characteristics	Aromatic Characteristics
X16	→Rapid fermentative kinetics →Alcohol tolerance up to 16% per volume →Tolerance to low temperature fermentation (53 ℉) →Low nitrogen requirements →Tolerance to low turbidity →Low production of volatile acidity and H2S	→Very high aromatic production of white peach, white flowers and yellow fruit
CH9	→Alcohol tolerance up to 16% per volume →Fermentation temperature: 57 – 60 °F →Average nitrogen requirements →Short lag phase	→Fresh almond and hazelnut, toasted bread and citrus fruits
D47	→Alcohol tolerance to 15% per volume →Low nitrogen demand →Short lag phase and moderate fermentation vigor →Low to moderate production of H2S →Ideal for barrel fermentation	→When left on lees spicy, tropical, citrus notes develop and the wine is said to have a silky persistence

The fermentation step of the wines inoculated with CH9 and D47 took more than three weeks to go to dryness. The fermentation inoculated with X16 took about 6 weeks to complete because we kept the temperature around (53 ℉). We took the fermented wine data and it looks like this:

Variety	Yeast	Volume of Wine	pH	TA
Chardonnay	X16	12 gallons	3.24	12.8 g/L
Chardonnay	CH9	6 gallons	3.20	10.4 g/L
Chardonnay	D47	6 gallons	3.15	13.2 g/L

The Microbial Community of Grape Berry - Part 3

In the first blog, The Microbial Community of Grape Berry, the topic was about the four groups of microorganisms that include (1) residents, (2) adventitious, (3) invaders, and (4) opportunists that can populate the grape berry.
The second blog The Microbial Community of Grape Berry - Part 2 was about the grape berry cuticle and the important role it plays in protecting the grape berry.
In today's blog we bring both topics together and ask, when are these four groups of microorganisms on the grape berry and what impact does it have on the condition of the berry?
The answer to this question depends fundamentally on:

• the berry development stage
• the intactness of the grape skin
• the prevailing environmental conditions

The Berry Development Stage
Grape berry development consists of two distinct but successive sigmoidal growth periods separated by a lag phase.
The first, the berry formation stage, also termed herbaceous or green phase, is the first period of growth, lasting from bloom to approximately 60 days afterwards.
Veraison or the ripening stage occurs 8-14 weeks after flowering and begins the second growth phase typified by sugar accumulation, skin softening , and skin coloration in the case of red varieties. The second period of growth is to make the berry as appealing as possible to birds and mammals so that seed dispersal may occur.
The following diagram clearly shows the berry development stage and the microorganisms that are prevalent at that stage.¹

• resident microorganisms are present on healthy grape surfaces at all times during their development
• invader infections occur essentially during the berry formation stage
• opportunist infections are concentrated during the berry ripening phase

Intact Berries

• in intact berries, the residents will be most prevalent.
• the residents can be rapidly superseded by the invaders or the opportunists when they proliferate through a berry wound, either of abiotic (i.e. rainfall, wind, temperature, viticultural practices, etc.) or biotic (i.e., diseases, pests, an insect or a larger animal) origin that can affect skin integrity.
• loss of skin integrity paves the way for massive growth of opportunists adapted to the low pH (3.0 to 3.8) and high sugar concentration (ca. 200 g.L-1) of grape juice
• the wound largely influences the microbiota which subsequently colonizes the damaged grape since it will induce a rapid change in the blend of grapevine volatile organic compounds (VOCs) emitted.
• G. Oxydans, predominates in sound berries, but is superseded by Gluconoacetobacter and Acetobacter, namely A. aceti and A. pasteurianus, in rotten berries.
• B. cinerea, the causal agent of grey rot, responsible for intense damage when rainfall is abundant, especially towards the end of grape ripening, as a result of berry splitting
• damaged grapes possess much higher cell counts (up to 5 log cycles) and display wider species diversity than sound grapes

Prevailing Environmental Conditions

• Downy Mildew
  →when warm and wet weather conditions prevail during the vegetative growth of the vine, downy mildew caused by the oomycete, obligate biotroph Plasmopara viticola is one of the most widespread and destructive diseases of grapevine
  →spring and summer rainfall at temperatures above 50ºF releases the oospores which is the primary inoculum
  →the occurrence, development and spread of disease are mainly dependent on rainfall and temperature
  → oospore, the primary source of infection, germinates on moist soil or in the presence of free water when temperatures rise above 11 ^oC, producing sporangia
  
• Powdery Mildew
  →Erysiphe necator is also known as Uncinula necator and is commonly called oidium
  →prefers mild temperatures between 68 and 85°F, relative humidity levels above 75%, and low levels of solar radiation
  
• Botrytis cinerea
  →under cool, wet and humid conditions, Botrytis bunch rot which favour sporulation and infection occurs
  →the severity of the infection by the fungus requires at least 25 h at 15-20 °C and saturated relative humidity
  →berry wounds constitute a preferential way for B. cinerea entry since it is an opportunist
  →susceptibility of grapes to this infection has been shown to greatly increase at the onset of grape ripening (veraison)
  →high free water level, suitable temperature and the presence of nutrients on the skin surface are necessary to induce spore germination and fungal growth
  

References:
1. V. Loureiro, M. M. Ferreira1, S. Monteiro1 and R. B. Ferreira, "The Microbial Community of Grape Berry", The Biochemistry of the Grape Berry, Chapter 12, 2012, 241-268.

Sugar in Grape Berry and Wine---Sugar Fermentation

The companion blog to this was called Sugar in Grape Berry and Wine---Sugar Transport and Accumulation in Berry, this blog picks up the fate of sugar after harvest.
One secret to making great wine is to find/grow high quality berries and ensuring that they are harvested in optimal condition.
During the fermentation process, glucose and fructose, the two major sugars of berries, are converted into alcohol by the action of the yeast Saccharomyces cerevisiae, releasing carbon dioxide and heat.

Winemakers control the fermentation through several parameters:

• temperature
• skin contact time
• pressing technique
• other techniques

The fermenting yeast S. cerevisiae has several hexose transporters (encoded by HXT1-HXT17 and GAL2), six of which (Hxt1-4p and Hxt6-7p) have been characterized as the most physiologically relevant. During must fermentation they perform different roles, and have different expression patterns according to their regulatory and kinetic properties:

• HXT2 is expressed essentially in the lag phase
• HXT1 is then expressed from the beginning of fermentation to the stationary phase
• HXT3 is present throughout fermentation, with a maximal expression when growth stops
• HXT6 and HXT7 are induced at the entry of stationary phase and remain expressed till the end of fermentation

These hexose transporters have a preference for glucose so towards the end of fermentation there is a prevalence of fructose. In addition to fructose, wines also contain small amounts of other sugars, such as arabinose, xylose, ribose, rhamnose, galactose, etc. The residual sugar in dry wines is enough to add mouth-feel without a perceivable sweet taste, and can balance the wine, and increase viscosity.
References:
1. Carlos Conde, Paulo Silva, Natacha Fontes, Alberto C. P. Dias, Rui M. Tavares, Maria J. Sousa, Alice Agasse, Serge Delrot, Hernâni Gerós, Biochemical changes throughout Grape Berry development and fruit and wine quality, Food, 1(1), 1-22 ©2007 Global Science Books.

Véraison: How the Grape Berry Gets Sweet

Véraison, is the onset of ripening in the grape berry. This is where the grapes enter the second rapid growth phase and is marked by the rapid increase in both the berry volume, soluble sugar accumulation and a rapid decrease of the organic acid contents. In other words, the grape is beginning to get sweeter, tastier and less acidic.
The transition from the lag phase to véraison is a critical development checkpoint in the grape berry and can last for 1 to 2 days.¹
At véraison, water import into the grape berry shifts from the xylem to the phloem. (Please checkout my blogpost: Grape Berry Circulatory System). Before véraison, the xylem is the main pipeline that delivers water, mineral nutrients, and growth regulators from the root system to the rest of the vine, including the developing grape berry. Water can move in and out of the berry through the xylem.
The phloem, is the vascular pathway that brings the photosynthates or the sugary solution made from photosynthesis by the leaf (the source), into the berry (the sink). The phloem can transport the photosynthates only one way, from the leaves to the berries.
This sugar concentration delivered by the phloem is mainly determined by the grape genotype but the environment, temperature and cultural management such as irrigation can have an impact on the final sugar concentration.
The phloem delivers sugar in the form of the dissacharide sucrose which is comprised of one molecule of glucose and one molecule of frustose. (Please checkout my blogpost: Sugar in Grape Berry and Wine---Sugar Transport and Accumulation in Berry). The uptake of sugar in the grape berry can be affected by various parameters including:²

• light
• water
• ion status
• wounding
• fungal and bacterial attacks
• hormones

Massive accumulation of glucose and fructose in the vacuoles of mesocarp cells in the grape berry occurs after véraison. This is accomplished through the action of an enzyme called an invertase that converts the dissacharide sucrose via hydrolysis, into it's components, glucose and fructose. Different invertase isoforms are localized in the cell wall, cytoplasm and vacuole.
Before ripening, the level of total soluble sugars in the phloem of the pedicel of grape berry is lower than 50 mM, whereas it reaches more than 500 mM at the beginning of ripening and 1,000 mM at the late ripening stage!
References:
1. Xiao-Yan Zhang, Xiu-Ling Wang, Xiao-Fang Wang, Guo-Hai Xia, Qiu-Hong Pan, Ren-Chun Fan, Fu-Qing Wu, Xiang-Chun Yu, and Da-Peng Zhang, "A Shift of Phloem Unloading from Symplasmic to Apoplasmic Pathway Is Involved in Developmental Onset of Ripening in Grape Berry", Plant Physiology, September 2006, Vol. 142, pp. 220–232.
2. António Manuel Jordão, F. Cosme, and Alice Vilela, From Sugar of Grape to Alcohol of Wine: Sensorial Impact of Alcohol in Wine, Beverages, 2015, 1, 292-310.

Auxerrois at Véraison

Our Auxerrois is always the first to come out of lag phase following the first growth period. My vineyard buddy, Bella and I noticed the softening of the Auxerrois when we were working on the Chenin Blanc which is adjacent to the Auxerrois. After handling the Chenin Blanc, the Auxerrois grapes felt much softer indicating that it was in the ripening phase.
I had my refractometer on August 15 and in checking the Brix of one grape, the Auxerrois was at 10^o Brix. On Sunday, August 18th we tasted a few grapes and the Brix at that time was 12^o Brix. The grapes are definitely taking on flavors but are still a bit tart. Time to do lab work with a repesentative sampling of grapes to measure Brix, pH and titratable acids.

Grape Berry Development - Heading into Véraison

Right around this time of the year is a good time to review a very relevant article called Understanding berry development by James Kennedy.
August is typically the month that our grapes enter véraison or the onset of ripening. The grapes have been in the first growth stage and are now in the lag phase. This stage lasts approximately 60 days after bloom. In our case, since our bloom occurred during mid-June, we would expect véraison to begin around mid-August.¹

Another way to look at the same information is:²

A grape berry only starts to accumulate significant sugars from the time of véraison indicated by:

• berry softening
• skin colour changing
• recommencing of rapid growth

This dramatic increase in sugar accumulation at véraison is accompanied by profound physiological variations:³

• sugar phloem loading shifts from symplasmic to apoplasmic pathway
• transcription of some genes encoding sugar transporters is enhanced
• activity and expression of key sugar metabolism enzymes are increased
• water influx pathway changes from predominantly xylem to phloem

Here is yet another way to look at the grape berry development path:⁴

References:
1. Illustration of the double sigmoid curve from: Moschou, Panagiotis & Aziz, Aziz & Roubelakis-Angelakis, Kalliopi, Chapter 7, Polyamines and grape berry development, The Biochemistry of the Grape Berry, (2012), 137-159.
2. Kennedy, James, Understanding berry development, Practical Winery and Vineyard, 2002, 24.
3. Zhan Wu Dai, Philippe Vivin, Thierry Robert, Sylvie Milin, Shao Hua Li and Michel Génard, "Model-based analysis of sugar accumulation in response to source–sink ratio and water supply in grape (Vitis vinifera) berries", Functional Plant Biology, 2009, 36, 527–540.
4. Rogiers Suzy Y., Coetzee Zelmari A., Walker Rob R., Deloire Alain, Tyerman Stephen D., "Potassium in the Grape (Vitis vinifera L.) Berry: Transport and Function", Frontiers in Plant Science, Volume 8, 2017, pg. 1629.
5. Xiao-Yan Zhang, Xiu-Ling Wang, Xiao-Fang Wang, Guo-Hai Xia, Qiu-Hong Pan, Ren-Chun Fan, Fu-Qing Wu, Xiang-Chun Yu, and Da-Peng Zhang, "A Shift of Phloem Unloading from Symplasmic to Apoplasmic Pathway Is Involved in Developmental Onset of Ripening in Grape Berry", Plant Physiology, September 2006, Vol. 142, pp. 220–232.

Vintage Notes 2025: The Auxerrois is at Veraison

We are splitting work duties in the vineyard. My husband is working in the Chenin Blanc and I am working in the Auxerrois. I can tell that the grapes are coming out of their lag phase, the time after berry set where the grapes stop growing. For white grapes, the "tell" that they are in veraison, or the beginning of ripening is when the berry becomes soft to the touch. For a few days now, I have noticed that the Auxerrois is soft when I handle it so I was curious to know what the Brix was. Yesterday, I brought the hand held refractometer to the vineyard and was surprised when taking the reading that the soft Auxerrois berries were at 15 ^oBrix! The slightly greener berries were at 13 ^oBrix.
Here is a photo of the Auxerrois. We only see this in the Auxerrois, where sometimes there are three clusters to a shoot.

It seems early to me that the Auxerrois is already this far along in sugar accumulation. I need to update my chart of the annual cycle of growth. All this means is that we need to bring the nets down in the next few days to protect the ripening grapes!

Vintage 2021: August Heat Wave

Mid-August finds us in the middle of a heat wave that began on August 11 and continued until August 14. Anytime the weather map looks like this is a good time to head for the cool indoors.

The heat wave may be compensating for what we thought would be véraison that would be a little later this year. We know that the Auxerrois is the first to ripen so we were busy netting our grapes. We had help during the heat wave on Saturday and now all five rows of Auxerrois have been netted!
This will be the first time that we have netted the Auxerois before the birds begin pecking at the sweet grapes. We do this so that the bird pecking which lures fruit flies and other insects won't have the opportunity to turn a beautiful bunch of grapes into a rotten mess!
You can use your senses to tell if the grapes are approaching véraison. The grapes will begin to soften and will feel different when you touch it from grapes that are still in the first growth and lag phase. You can also taste the grapes to see if they are sweet.

On August 12, I brought our hand held refractometer to the vineyard to check on the Brix of the Auxerrois. It was at 11 ^oBrix. I tasted one of the Auxerrois grapes and it was still very acidic, so not yet a tasty treat for birds.

Getting Ready to Make Wine

We made our annual trek to Musto Wines Grape Company to get our yeast in preparation for making wine. Over the years, we did our homework and researched some of the yeasts that we were interested in using to ferment our white and red varieties. We used the Scott Laboratories Handbook and have settled on a few yeasts that we feel are the right fit for the grape varieties that we grow.

Variety	Yeast	Yeast Characteristics
Auxerrois	QA23	S. cerevisiae bayanus Alcohol tolerance 16% YAN requirements: Low Temperature range: 59 - 90 °F Fermentation speed: fast Competitive factor: Yes MLF compatibility: Very good Sensory effect: Evc Fruity (esters) Tropical (thiols) Citrus (esters and thios) Floral Spicy Aromatic whites: Chardonnay, Sauvignon Blanc
Chenin Blanc	QA23	S. cerevisiae bayanus Alcohol tolerance 16% YAN requirements: Low Temperature range: 59 - 90 °F Fermentation speed: fast Competitive factor: Yes MLF compatibility: Very good Sensory effect: Evc Fruity (esters) Tropical (thiols) Citrus (esters and thios) Floral Spicy Aromatic whites: Chardonnay, Sauvignon Blanc
Chardonnay	D47	S. cerevisiae cerevisiae Alcohol tolerance 15% YAN requirements: Low Temperature range: 60 - 82 °F Fermentation speed: moderate Competitive factor: Yes MLF compatibility: Very good Sensory effect: Evc, M Fruity (esters) Citrus (esters and thios) Floral Mouthfeel Aromatic whites: Chardonnay Rhône Style Whites Rosé Suitable for barrel fermentation
Cabernet Sauvignon	F15	S. cerevisiae cerevisiae Alcohol tolerance 16% YAN requirements: Medium Temperature range: 68 - 89.6 °F Fermentation speed: moderate F15 is for the production of fruity, well-balanced red wines with good mouthfeel (high glycerol production). It is suitable for the vinification of musts with potentially high alcohol concentrations, especially Merlot, Cabernet Sauvignon and Zinfandel.
Cabernet Franc	FX10	S. cerevisiae cerevisiae Alcohol tolerance 16% YAN requirements: Low Temperature range: 68 - 95°F FX10 is for the production of elegant wine, with more volume on the palate (polysaccharides) and silky tannins.
Barbera	F83	S. cerevisiae cerevisiae Alcohol tolerance 16.5% YAN requirements: Low Temperature range: 68 - 86 °F Fermentation speed: moderate F83 has been selected for its ability to produce fruity, round, supple wines for early release on the market. Due to its short lag phase and easy implementation, ZYMAFLORE® F83 guarantees efficient and complete fermentations.

Here is the link to the Scott Laboratories Handbook, it is a very handy reference to have:
Scott Laboratories Handbook

Effect of Heat Wave on Grape Leaf Stomata

We are in for a heat wave in the Northeast and may be setting some record temperatures. I wondered what effect this will have on the grapevines. I learned in the UConn Master Gardener course that when the temperatures get too high, this adversely affects sugar accumulation. When I first heard that I was really puzzled. In order to understand this conundrum, I needed to learn about the functions of the grape leaf stomata. The image on the right shows the stomata which are located on the underside of the grape leaf.¹ The stomata functions in the evaporation of water as well as in gas exchange. Carbon dioxide entering through the stomata is converted to carbohydrates via photosynthesis. When temperatures approach 100^o F, the stomata on the leaves close in order to conserve water and the translocation of carbohydrates to the grapes stops. We may actually be okay because I believe that the grapes are currently in the lag phase of their growth. (See Vine Growth) However, if the grapes are in veraison, even 3-4 days of excessively high temperatures (>105^o F) may retard ripening. Once temperatures have returned to normal, sugar accumulation can resume.²
1. Regents Biology Chapter 19
2. Nick Dokoozlian Grape Berry Browth and Development

Waiting for Cup Airlock Bubbling

My husband and I started the fermentation of our Auxerrois at 8 p.m. on September 25th. This is a tense time of waiting for bubbling from the airlock, especially when the fermentation is in a non-see through stainless keg. I was trying to convince myself that I could actually smell the beginnings of fermentation, each time I lifted the freezer lid to check on the airlock. This morning, a full 60 hours after the yeasts were put into the keg, I was having serious doubts about my yeast rehydration procedure and was wondering if I needed to rehydrate another batch of yeast.

It turned out that I didn't need to worry because this year, my husband decided to invest in a micro inspection camera. The camera came yesterday and my husband tested it out last night. Around 9:30 a.m. this morning, he set up the device and we went down into our fermentation cave (aka basement) to check on the Auxerrois. Using his micro inspection camera, we found that although the bubbler was mute, the yeast were in an active state of reproduction! This stage is probably part of the lag phase where the yeasts are undergoing rapid division. Once we opened the keg to look inside and resealed it, the bubbler started to show signs of carbon dioxide evolution. I know, Murphy's Law, right!

Malic Acid in Grapes: Part 3 The Importance of Acidity

I am back to doing more digging into the role of malic acid. I have blogged about tartaric and malic acids in the following posts:

• Malic Acid in Grapes: Part 1 Our Titratable Acid Conundrum
• Malic Acid in Grapes: Part 2 Chemical Structure and pKa

In the first blogpost, I wrote about the conundrum we faced when our red grapes were harvested at a very nice level of Brix, but the titratable acidity was very high. In the second blogpost, I wrote about the chemical structures of the two most prevalent acids in grapes and how they respond in a juice/wine environment based on pH.
In this blogpost, I will try to further elaborate on the roles that both malic and tartaric acid play in the ripening grapes.
Why is acidity important?:

• it influences the ageing potential or the shelf-life of wine
• it determines the physical, biochemical and microbial stability of wine
• it ultimately determines wine quality in terms of the perceived organoleptic and aesthetic character

Without acidity, a wine can be very flabby and unbalanced. With the appropriate levels of acidity, a wine can become sublime. But knowing what the right level of acidity is, is a tricky business.
The principal organic acids in grapes are L-tartaric and L-malic acid. L-tartaric acid is often found at higher concentrations than L-malic acid and is the stronger acid of the two. I have already blogged about the Two Stages of Grape Berry Development. During the first stage of berry development, there is the rapid storage of L-malic and L-tartaric acid in the vacuoles leading to an increase in size of the grape berry cells. During the lag phase between stage 1 and stage 2 of berry development, berry acidity reaches a maximum concentration. The concentration of L-tartaric acid is relatively constant, while L-malic acid is the only high proportion organic acid that is actively metabolized throughout the ripening of grapes.
It is this metabolism of L-malic acid that is important to us in trying to understand what happened this year when our Brix level was high and our titratable acid was high in our Cabernet Sauvignon and our Cabernet Franc. Stay tuned for more about malic acid metabolism.
References:
1. H. Volschenk , H.J.J. van Vuuren and M. Viljoen-Bloom, "Malic Acid in Wine: Origin, Function and Metabolism during Vinification", South African Journal of Enology & Viticulture, 27(2):123-136, doi:10.21548/27-2-1613.
2. Crystal Sweetman, Laurent G. Deluc, Grant R. Cramer, Christopher M.Ford, and Kathleen L.Soole, "Regulation of malate metabolism in grape berry and other developing fruits", Phytochemistry, Volume 70, Issues 11–12, July–August 2009, Pages 1329-1344.