🌿 Grape harvest

Grape harvest is the picking of grapes from the vines. For wine, the date is set by ripeness, which growers follow by measuring the grapes.

University extension guidance names three main measurements: soluble solids (°Brix, read with a refractometer), titratable acidity and pH. Ohio State University Extension gives general wine grape targets at harvest of 18 to 24 °Brix depending on variety and wine style, titratable acidity of 0.6 to 0.8 g/100 mL, and pH of 3.1 to 3.3 for white and 3.3 to 3.5 for red grapes. It advises sampling at least 200 berries per block and variety, from at least 10% of the vines, from both sides of the trellis and from the top, middle and bottom of clusters. The University of Georgia adds that sugar is the most widely used index, that many growers also check seed colour, flavour and aroma, or phenolic maturity in reds, and that a pH above 3.9 raises the risk of microbial spoilage.

Grapes are picked by hand or by machine. UC Davis extension slides list pivotal strikers and trunk shakers as the main picking systems of grape harvesters. Machine harvest gives the grower control of peak ripeness because it is fast, but it needs a suitable trellis and correctly spaced rows, and it brings in material other than grapes (MOG).

In a 1980 study in Vitis on Chenin blanc in South Africa, alternate rows were picked by hand and by machine. A higher picking temperature, a longer wait before winemaking and more MOG raised the total polyphenols in the wines and lowered their sensory quality. Grapes picked at low temperature showed no adverse effect after a wait of up to 4 hours.