Wine Quality Factor: Vineyard Management
Trellising systems influence how vigorous a grapevine becomes and how much sun exposure it receives; factors which in turn influence how grape berries and clusters ripen. Vigorous rootstock can lead to vines that are very productive—productive enough for areas where five to ten tons of fruit per acre is the desired yield and ordinary table wines are the end result. Conversely, devigorating rootstock leads to less vigorous vines and is preferred by vintners seeking a smaller crop and superior quality.
The basic fact to keep in mind is this: crop yield is crucial to a wine's quality. The lower the grape yield per acre, the more concentrated the juice will be. This is a very important factor which is considered in the overall cost of a wine. A vine tries to ripen all of its berries. If it is carrying many clusters, it has to work harder and longer to supply the nutrients to ripen all of the berries. If the vine is bearing too many grapes, often it will stop short of maturation, resulting in wines which have an unripe flavor. Therefore, many high quality producers are in the vineyards pruning leaves to allow more sunlight to reach the grape clusters and dropping grape clusters which are not as ripe and developed as others on the vine, to assure even ripening.