Beginning with bud break in mid-May, it had been almost four months since the start of the 2020 growing season. The vines had been occupied with creating energy and resources through photosynthesis. There had been little disease or insect pressure, as the weather had remained warm and dry through the summer.
The development of grape berries can be split up into three stages.
The first stage commences at fruit set, when the berries experience rapid cell division and acid accumulation, culminating in berries that are roughly half their eventual size.
The growth pauses at the onset of stage two, dedicated to seed growth and chemical changes to prepare the fruit for the final stage. At the end of stage two, the berries are dark green, hard as marbles, bitter and acidic, quite unsavory to taste.
Then Mother Nature throws a switch, and thousands of genes kick in or are repressed to perform a magic trick — véraison. It’s the start of stage 3 of berry development. Véraison offers a highly visual cue by changing the berries’ color. Red wine grapes begin to take on a hue of red, while white wine grapes start to turn more translucent with subtle yellow and gold tones.
In many wine producing regions in the world, véraison is a time for celebration, as it signifies the onset of the ripening of the grapes.
September 4, 2020
On a beautiful, sunny day (like just about every other day that summer) I stopped by the Hosmer vineyard to check on our riesling vine in row 18, as véraison has begun. The sea of dark green color was now tempered by the soft yellow glow of the berries.
Cameron Hosmer was away this morning, so I wandered through a few rows of riesling vines by myself. The vines all looked remarkably clean and healthy. The drought had not affected them as the long roots of the old vines (planted around 1980) had no difficulty finding moisture in the depths of the highly organic soil.
In rieslings and other white wine grapes, the color transformation of the berry skin is caused by the breakdown of chlorophyll in the skins, exposing the underlying carotenoids — the same pigments that give carrots an orange and corn a yellow color. A group of chemical compounds called Flavonols acts as sunscreen to protect the berries as the skin softens and becomes more elastic, making it possible to accommodate a rapid expansion of the berries. Flavonols also provide tannins, found mostly in the seeds and skins of the grapes.
The hard berries become softened when the cell walls of the pulp break down, allowing the berries to enlarge through the intake of water, which would wind up constituting up to 80% of the weight of the berries by harvest time. Sugar, attained in the form of sucrose, is mostly broken down into glucose and fructose in the process, making the grapes increasingly sweet to taste. Aroma and flavor compounds continue to amass in the grapes to enhance their complexity and taste. Acidity is reduced and toned-down. The berries are turning from inedible to delectable.
All these changes are for the benefit of an innate evolutionary goal — the propagation of the species, by making the grapes delicious to attract birds and animals to digest the berries and distribute the seeds.
September 24, 2020
During the previous week, nighttime temperatures dropped below freezing during several nights on the east side of Cayuga Lake, where I lived. I drove over to Hosmer today to see if there was any cold damage to our riesling vine.
“I heard my neighbor’s wind machine come on one night and I woke up to run my own machines. Luckily, it never dropped below 34 degrees,” said Cameron Hosmer. “I was up four nights in a row to check the temperature.”
He added, “The magic number for damage is about 28 degrees, when grape tissues begin to freeze.” Ideally, you want warm days and cool but not freezing nights. Cooler temperatures during the day at this juncture retard ripening, slowing the accumulation of sugar and other compounds. The period from véraison to harvest is a critical time that has a huge impact on the quality of a vintage.
While most other grape varieties have already been harvested, riesling and cabernet franc are usually the last two to be picked. “The warm summer really helped. The cold last week was just a blip,” said Hosmer. “We are probably two solid weeks before starting to pick.”
Two weeks might not sound like a long time, but the grapes were currently quite vulnerable. Hosmer explained, “The grapes are fragile now. The skins are thin and they are susceptible to rot.”
To birds and animals, the sweet and luscious grapes represent wonderful treats. Hosmer said, “We have a squawker that makes distress calls to ward off birds. We also use cannons, although that made the cops come one night when we forgot and left it on all night.”
Everything is pointing to an outstanding vintage in the making. But many a promising vintage had been ruined by poor conditions at harvest time. Could this weather hang on for just two more weeks?