🌿 Yield (wine)

Yield in viticulture is the amount of crop a vineyard gives per unit of area, for example tons per acre. It follows from a few components: row spacing, the number of shoots per linear foot of trellis, the number of clusters per shoot and the weight of a cluster. In a Penn State Extension example, with rows 9 feet apart, 1.5 clusters per shoot and 120 g clusters, yield is roughly 3.8 tons per acre at 4 shoots per foot of trellis and roughly 4.8 tons per acre at 5 shoots per foot, assuming no losses to pests.

Growers regulate yield in steps. Dormant pruning is the first, because clusters arise from the buds that are retained. Shoot thinning is the second: it removes basal, latent, unfruitful, diseased or malformed shoots, aiming at roughly 3 to 5 shoots per linear foot of trellis. Cane-pruned vines produce fewer shoots than spur-pruned ones (19 to 24 against 44 to 46 shoots per vine in the table quoted by Penn State), so they need less thinning. Divided canopies and double-cordon systems usually carry more shoots per vine.

A crop that is too high is a risk. An excessive crop may fail to reach commercial maturity in a timely manner, clusters touch and bunch rot increases, and wine quality potential can fall, with poor colour and varietal character in congested clusters.

Yield is also a matter of law. Under Regulation (EU) No 1308/2013, the product specification of a protected designation of origin or geographical indication wine must state the maximum yields per hectare. The same regulation defines green harvesting, for the purposes of wine support programmes, as the total destruction or removal of grape bunches while still immature, reducing the yield of the area concerned to zero.