Definition - What does Fruit Set mean?
Fruit set is part of the grape growing season as it denotes the time in which the flowering clusters turn into berries. The flowering part of the vine has hundreds of flowers but only 30-50% of these should become berries and any more than this ratio can lead to poor fruit set.
The flowers naturally shed during the berry shatter period and the berries that become grapes are known as the fruit set.
WineFrog explains Fruit Set
The fruit set of the vine is dependent on the variety, the wine growing region and the environmental conditions of that particular year. The best conditions for a good fruit set are mild temperatures, long sunny days, good soil water saturation and dense nutrients. Since the fruit set is a representation of the health of the vine, it can be impacted by poor weather conditions, stressors like pests or disease and poor water or too little sunlight exposure. The number of flowers doesn’t always depict how the fruit set will turn out, only the berries that achieve their full desired size are considered the fruit set. A reduced number of berries or berries that don’t develop and stay small, green and without seeds would contribute to a poor fruit set.