The winter months are an important part of the California table grape growing cycle. Growth and development stop temporarily and the vine rests. This stage is called “dormancy.” At this time, growers prune the vine and set it up for the upcoming cycle to begin. Pruning and training of the vine are two of the most important aspects for quality grape production – growers decide how much and which parts of the previous season’s growth to remove in order to regulate vegetative growth (shoots and leaves) and crop load (grape clusters) to produce quality grapes and optimum yield.
In early spring tiny buds on the vine start to swell and green leaves appear. Appearance of the first green leaves through the bud scales is called budbreak. Growth is slow at first. As the mean temperature rises, growth and shoot elongation accelerate. After three or four weeks, the period of most rapid growth begins – where shoots can grow an average of one inch or more per day. As the days warm up, flowers bloom, then shatter to make way for the tiny green grapes that will eventually ripen into clusters. Berry size increases rapidly. Sunlight and warm temperatures are vital to the physiological functions of the grapevine (such as photosynthesis).
The point in the growing season when ripening grapes begin to soften is called “veraison.” During ripening, colored varieties gradually change color from green to either red or black, while green varieties become translucent. Sugars start to accumulate in the berries. The interval from veraison to harvest is different for each variety. Unlike many fresh fruits, grapes are harvested fully ripe. After they’re picked, they do not become sweeter, so timing is everything.
Determining when grapes are ripe is a real science and both the U.S. Department of Agriculture and California Department of Food and Agriculture are involved in setting and monitoring grape production standards. Sugar content, color, bunch and berry size and uniformity are all measured before harvest begins and the workers who decide which grapes to clip are trained professionals with years of experience.
Once picked, fresh grapes are easily damaged by rough handling, warm temperatures, excessive moisture and decay-causing organisms. Consequently, grape bunches are carefully inspected and then immediately packed by hand into shipping containers — sometimes right in the field. Shortly after picking, the field heat is removed from the fruit in cold storage facilities. From this point until they reach their destination — markets throughout the world — the grapes will be maintained in a carefully regulated environment to assure they arrive in just-picked condition.