Grape growing, winemaking and wine maturation

A vine’s growth cycle begins with dormancy, which is the end of one cycle and the beginning of another. Dormancy begins with leaf fall in the autumn and ends with bud break in the spring, when the average daily temperature reaches approximately 50ºF (8-10ºC).

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At the end of dormancy, sap rises through the roots and flows through the vine, causing the buds to swell. Most will burst–some will remain dormant. There are two types of buds: leaf buds and fruit buds, which are identical at bud break. The rate of growth of the shoots or leaves depends on the reserves of carbohydrates in the vine. Growth is slow at first and then accelerates, reaching its peak just before flowering. The speed of growth drops off rapidly at flowering, but growth continues through the season, stopping only at veraison, or when the grapes change color and begin to ripen. Shoots at this stage begin photosynthesis.

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Fruit buds contain the beginnings of flower clusters. The length of time from leafing to flowering is about eight weeks. The number of fruit buds formed and ultimate yield of the vine, depends on many factors, including carbohydrate accumulation in the vine, nitrogen and water supply, and climate.

The flower caps that cover the stamens fall off after flowering so that the stigma can receive pollen. The fertilization of the flowers leads to berry set. Most flowers self-pollinate, with all flowers having both stamens and pistils. Weather at this stage is crucial because poor weather can stop the fertilization from occurring, reducing the amount of clusters that each vine carries. In successful flowering, about 30% of the flowers become grape clusters. If flowering is disrupted by poor weather, yield is reduced and the result is known as shatter or coulure. If the unfertilized flowers do not drop off the vine, they form small hard berries with no seeds called shot berries or 'millerandage.' If the vine lacks carbohydrates because of insufficient photosynthesis or excessive shoot growth, flowers can fall off more easily, leading to this condition. It can also be caused by mineral deficiency, viral infection or old vine age.

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Approximately 40-50 days after fruit set, the berries turn color in the veraison process and begin to ripen. As ripening continues, the grapes soften and their volume increases while the acidity of the grapes decreases. During ripening, the growth of the shoots ceases, so that all of the vine’s nutrition can go to the fruit. Mature, ripe fruit has a good balance between the sugar and acidity. The exact moment of this balance is an individual decision and calculation made by each grower based on the year’s crop.

In addition to balance, ripeness also depends on maturity of the phenolic compounds in the grape. These compounds are the tannins and coloring agents that are present in the skin, seeds and stems. If harvest occurs before they are ripe, the tannins will be hard and unyielding and the wine will have green, unripe flavors.

After harvest, the leaves fall and the vine enters dormancy once again.

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All vineyard treatments are stopped long before harvest to ensure that residue from pesticides does not get into the wine. During this period, growers sample the grapes in the vineyard regularly to determine when the desired level of ripeness is attained. The grower determines the balance of sugar, acid and phenolic ripeness desired and thus decides picking time. In addition to tasting the grapes to determine ripeness levels and phenolic maturity of the grapes, almost every winemaker also utilizes lab analyses with detailed information on acidity, alcohol, anthocyanins, tannins and polyphenols.

Harvest can be done in most regions either by hand, by pickers cutting individual bunches and laying them in small baskets, or by machine. Hand harvesting is mandatory in some regions such as Champagne.

Although hand harvesting is gentler it is slower and more expensive. Handpicked grapes tend to suffer less damage during the harvest. However, in cases where the harvest needs to be completed quickly, such as threatening weather or rapidly falling acidity due to heat spikes, machine harvest can be preferable.

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