Vintage 2020: April Weather

I have written about the April weather before. Check out these blogposts:
2019: April Update on our Buds
2018: Vintage 2018: Spring Chores
2017: Vintage Notes: April 2017
The common theme of all of the above blogposts was the rain days that we had in that year. I distinctly remember that last year, the old adage,
April showers bring May flowers, was modified by one of our friends to:
April showers bring May showers because of all of the rain that we had last spring.
So, keeping with the tradition, I decided to look back at April, 2020 to see what the rain situation was. I knew that we had a fair amount of rain, but in looking back, we had 10 days of rain in April. This is not counting the rain that occurred during the late night and early morning hours, because we were able to get into the vineyard to work.

In addition to the rain that we've had, on April 27, this past Monday, Connecticut recorded the lowest high temperature since 1917! It is no wonder that our buds have refused to come out of dormancy. Hopefully May will bring some warmer weather.

Organic Acids in Grape Berry and Wine---Malic Acid Metabolism

Malic Acid Metabolism Malic acid is accumulated in the fleshy cells at the end of the first growth phase, reaching its maximal value just prior to véraison.
Both leaves and immature green berries can form malic acid. Photosynthesis in the green berry is responsible for approximately 50% of the accumulating acids.
About 6 to 9 weeks after flowering and midway between bloom and fruit ripening, there is the simultaneous initiation of organic acid breakdown and sugar accumulation at the onset of ripening. When the grape berries begin ripening, the level of malic acid decreases due to malate oxidation.
What is known about the decrease in malic acid in the ripening grape:

• used as carbon and energy source for respiration
• cytosolic NADP-malic enzyme is considered to play a key role in the regulation of malic acid breakdown catalysing the oxidative decarboxylation of malic acid to pyruvate and CO₂
• diffusion of malic acid into the mitochondria and its subsequent degradation through the action of a mitochondrial malate dehydrogenase into oxaloacetate
• malic acid oxidation to pyruvate through the action of a mitochondrial NAD-malic enzyme
• cool regions typically produce grapes with higher concentration of malic acid and, conversely, grapes grown in warmer regions tend to have lower acidity; this negative temperature correlation with malic acid levels is due to the effect of temperature on the balance between malic acid synthesis and catabolism
• accumulation of potassium into the berries results in the formation of tartrate and malate salts, accounting also for a reduction of the total acid concentration
• despite their structural similarity, tartaric and malic acids are synthesized and degraded by markedly different biochemical processes

References:
1. The chemical structure of tartaric acid was drawn by the freely available drawing program from ACD Labs called ACD/ChemSketch Freeware.
2. 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.

First Spray of the Season: Lime-Sulfur

We almost never get a chance to do this but this year, we were able to prune all of our vines and lay down all of our canes in preparation for the first spray, lime-sulfur, a dormant spray. My husband modified our handy John Deere mower to accomodate a sprayer and hand sprayed mainly the trunks of our vines as well as some of our canes.

Next up of our list of many things to go is probably, mow the growing grass and weeds!

Organic Acids in Grape Berry and Wine

Tartaric Acid Metabolism

Here is an interesting factoid about tartaric acid: Grapes, the baobab tree and the tamarind fruit are the only plants that contain tartaric acid.
Given that tartaric acid is found in nature in a limited number of instances, it would be interesting to know how it is synthesized.

In grape berries, tartaric acid is synthesized beginning at flowering and ending at véraison.
References:
1. The chemical structure of tartaric acid was drawn by the freely available drawing program from ACD Labs called ACD/ChemSketch Freeware.
2. Patrick McGovern, Ancient Wine: The Search for the Origins of Viniculture.
3. 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.

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.

2017 Leonetti Merlot

We have been having FaceTime dinners with our friends. We get together on Thursday evenings and split the dinner making. Last night, our friends made grilled butterfly leg of lamb, green beans almondine and gruyere potatoes au gratin. It was delicious and we enjoyed their "company".
Not only that, we shared half of their bottle of 2017 Leonetti Merlot. It was dark inky, purple in the glass and had just enough fruit, but very nice acidity that went perfectly with the grilled lamb.
We have been fans of Leonetti for a long time. I remember road trips we used to take just to longingly stare at bottles of Leonetti at the Wine Stores. I learned a few things when I visited their website, Leonetti Cellar. In 1977, Gary and Nancy Figgins established Walla Walla, Washington's first commercial winery. At the present time, their son, Chris and daughter Amy run the operations.

Sugar in Grape Berry and Wine---Sugar Transport and Accumulation in Berry

Sugar in Grape Berry and Wine
Sugar transport and accumulation in berry

• Sucrose is a disaccharide sugar composed of one unit of glucose and one unit of fructose, as shown above
• Sucrose is produced through photosynthesis in the mesophyll of mature grape leaves
• The mesophyll of mature leaves are the "source tissue" and sucrose produced in the mesophyll are transported to the grape berries that are the “sink organs” which accumulates the sugar
• Sucrose is the major osmotically active constituent in the phloem and provides the driving force for translocating all other compounds in the phloem sap
• Massive accumulation of glucose and fructose in the vacuoles of mesocarp cells in the grape berry occurs after véraison
• The rapid accumulation of hexose characterizing berry ripening must involve the activity of invertases
• Invertases catalyse hydrolysis of sucrose provided by the phloem conducting complex into glucose and fructose; different invertase isoforms are localized in the cell wall, cytoplasm and vacuole
• Sugar accumulation in the berry is regulated by complex mechanisms and may be affected by various parameters including light, water and ion status, wounding, fungal and bacterial attacks, and hormones
• Once phloem transport has ended, any further increase in berry sugar concentration is exclusively due to water loss
• The fungus B. cinerea can thus act positively on the sugar content in matured berries and is used by grape growers to produce sweet wines
• Sugar content is an indicator often used to assess ripeness and to mark the harvest
• While indicating maturity level, “sugar ripeness” is not, by itself, the best index of optimal maturity
  
• Most of the sugar is fermented to ethanol during the wine making process, the measurement of sugar content, the so-called “must weight”, allows the control of alcohol content in the wine
  

References:
1. Text and 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.

Vintage 2020: Spring Help in the Vineyard

My husband and I are still pruning, but now we are interspersing laying down our canes, so the end of the pruning tunnel got a bit extended. In the meantime, we have a couple of friends, husband and wife, who have been helping us and have put us in a good place with what they do, all while maintaining the proper social distancing.
Recently, they came to help us plant some Barbera, replacing the ones that didn't make it from last year's planting.

In other news, our other friend who was allowing us to take our cuttings to his burn pile, set the pile up in flames.

That's all the news that is fit to print in this time of a global pandemic. Please stay safe!

Potassium in Grape Berry and Wine

Potassium is a cation that is present in both the grape berry and wine. Potassium in the Grape Berry
Grape berries are very rich in potassium which is an essential macronutrient for grapevine and grape berry growth and development:

• the levels of potassium in grape berries may be affected by numerous factors including potassium level in the soil, grape variety, and viticultural practices
• high permeability of plant membranes to potassium leads to a high concentration in plant tissues
• potassium is absorbed by the roots and distributed to all parts of the vine
• early in the season, when the growth rate is high, much of the potassium accumulates in the leaves
• during an initial rapid phase of berry growth, cells divide and expand at a high rate, during which time potassium may play an important role as an osmoregulator
• after véraison, a sharp increase in berry potassium is observed as a result of potassium redistribution from leaves to berries
• potassium may play an important secondary role in the accumulation of sugars during this phase
• grape skin contains about 9 grams of potassium per liter at harvest
• excessive levels of potassium in berries at harvest may reduce the quality of fruit and have a negative impact on wine quality, particularly on red wines

Potassium plays a key role in the grapevine physiology:

• enzyme activation
• major control on the transmembrane potential difference of the plasma membrane, which to a large extent determines the uptake of many different cations, anions and sugars
• regulation of osmotic potential, thus controlling plant water relations, turgor maintenance and growth
• high potassium levels in the berry may decrease the rate of malate degradation by impairing malate transport from the storage pools in the vacuole to the cytoplasm

Potassium in Wine

• potassium is the main cation in must and wine and can affect the pH which is a critical determinant of wine quality
• exchange of tartaric acid protons with potassium cations results in the formation of largely insoluble potassium bitartrate, leading to a decrease in free acid and tartrate:malate ratio, resulting in an increase of overall pH
• grape juice with a high pH often results in unstable musts and wines that are more susceptible to oxidative and microbiological spoilage
• wines with a high pH and low acidity generally have a flat taste
• high pH of grape juice and wine also leads to a decrease of the colour quality and stability of red wines as a result of reduced anthocyanins ionisation at higher pH
• grape juice contains from 0.5 to 3 grams of potassium per liter
• berry potassium levels are often more important to red than to white wines
• red wine fermentation involves leaving the skin in contact with the must after crushing for the extraction of anthocyanins, even more potassium can leach out of the skins into the juice at this time

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.

Vintage 2020: Still Pruning

On March 12, I wrote about Pruning Time and we are still pruning, but seeing the light at the end of the tunnel. One thing that changed for us is that we usually take our cuttings to the Transfer Station, aka town dump because we don't have a burn permit on our vineyard and on March 26, when we attempted to take the cuttings our town dump was closed!
My husband looked into this and found that we would have to make an appointment to take our trash to the dump 24 hours in advance. This is what life is like in our rural corner of Southeastern Connecticut, during the time of the coronavirus pandemic.
Thankfully, we have a friend who owns a huge property by the lake and he has a burn permit and is allowing us to take our cuttings there. So, from March 26, we have been taking our vineyard cuttings and this is what it looks like now. Our cuttings have a beautiful view of the lake.
Please stay safe during these uncertain times.

Water in Grape Berry and Wine

Water represents 90% of the harvest weight in a crop. When the crop is harvested and pressed, water can represent from 75-85% of the must and in the case of wine, can represent between 65-94%, depending on wine sugar content.
Vine growth and grape berry development are closely related to water availability in the soil and water availability in the soil is related to the Soil Texture and Water Holding Capacity.
Water Deficit:

• water deficit generally leads to smaller berries since it inhibits both cell division and, especially, cell expansion.
• timing of the water deficit is clearly important in order to determine fruit and wine composition
• irrigation can provide a means to manipulate wine sensory characteristics in the vineyard
• water deficit has a less pronounced effect on sugar accumulation than on berry growth
• when water deficit occurs post-véraison, fruit sugar is often reduced rather than being improved
• malate decrease occurs primarily when water deficit occurs before véraison

The Role of the Xylem and the Phloem

• The Grape Berry Circulatory System relies on the xylem and the phloem
• water influx into fruits occurs via both the xylem and phloem
• most of the berry volume gain before véraison is due to water import from the xylem
• most of the post-véraison gain is due to water import from the phloem
• at véraison, there is a substantial reduction in the proportion of water that is transported to the berry through the xylem compared to the phloem
• sugar accumulation in the grape berry is associated with the shift from xylem to phloem water transport at the transient onset of berry ripening
• the shift from xylem to phloem function at véraison would prevent a substantial water or solute backflow from the fruit to the plant

References:
1. Text and 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.