After preparing the area around our grape vines as described in last month’s “In Vigna Blog”…we now anxiously await the evolution of the grape.
Shortly after the vine’s canes have developed somewhat, we begin to see what appear to be miniature bunches of grapes about an inch long. Actually, they are not yet grapes, but are the vine’s flower buds or floral clusters. Approximately 45 days after the formation of flower buds, the clusters have grown to about 2 ½ inches long and “bloom” occurs.
Bloom is one of the wonders of nature that is the beginning of a grape. Each of what seemed to be a tiny berry in the little clusters is in fact a flower bud. Each flower in the cluster has its own stem, called a “pedicel,” and a protected cap, called the “corolla.” When bloom occurs, the corolla pops off to reveal an extremely delicate, tiny flower. The flower itself consists of a central female pistil which receives pollen. Surrounding the pistil, are five stamens, and white petals. The male stamens are composed of very fine, hair-like filaments, each holding a pollen sack.
The grape vine is hermaphroditic or “monoecious” to the botanist. In other words, grape vines are self-pollinating and don’t need the services of the bees. The pollen is discharged into the air, usually in the early morning hours as the temperature rises, breezes carry it to the female pistil where pollen is trapped and germination begins.
Pollination in the vineyards is usually completed within ten days to two weeks after bloom. What takes place during this critical stage is important to both the quantity and quality of the fruit. The microscopic pollen descends a tube in the center of the pistil to an ovary near its base. There, within a few days fertilization occurs. The ovary then develops into a green berry as the flower withers and falls off.
This transformation from flower into berry is what we call “set” or “berry set.” Not every flower converts into a berry that eventually becomes a grape. In some instances, no pollination takes place, and the berries that appear are said to have “shattered.” It is not uncommon for other blossoms to achieve only partial pollination, in this case the berries will mature and develop some sugar, but will be only a fraction of normal size. These are what we refer to as “shot berries.”
The relative successful “set” to vintners is very important. We don’t expect every flower bud to be transformed into a berry. Thankfully, the vine normally produces more flowers than are needed to give us a good crop. It is a successful set when 40% to 50% of the flowers are pollinated. Inhospitable weather during this critical 10-day period, in the form of frost, a hot spell or high winds, can result in very poor berry set with excessive shatter or shot berries. We also worry about a stretched out period of “bloom” and “set” which give us an irregular set. That means that in a given cluster, early pollinated berries will mature earlier than those pollinated much later. Come the harvest season, we will find a cluster with fully ripe grapes along with still green berries. Grapes optimally are picked cluster by cluster, irregular set is a situation that makes it difficult for us to determine when to harvest. It presents a real challenge for the winemaker to create a balanced wine. Obviously, we prefer both a good set in terms of quantity and a regular, even set, in terms of quality.
As vintners, we do what we can to assure fine quality before and after the “bloom” and “set” period. We plant the finest wine varieties in the ideal locations, cultivate the vineyards with the utmost care, harvest only when the grapes are at their optimum levels, and nurture the wine in the winery. But the greatest single factor in the ultimate grape and wine quality is controlled by Mother Nature. It has been, and will always be the case.