With harvest just over a month away, grape picking equipment is being fine tuned and tanks are being emptied to make room for the coming harvest. But how does a viticulturist determine when his or her grapes are ripe enough to pick?
There are several key factors that influence harvest decisions. The first is the brix (or sugar level) in the berries. Brix are, by definition, the grams of solid in 100 grams of liquid. Most of the solids are fermentable sugars but there is a small amount of non-fermentable solids, such as acid and aroma compounds. The brix number goes up as the summer goes on and each brix will ferment to roughly 0.6% alcohol (v/v).
The second key factor is the titratable acidity (TA) in the grape must. TA is the measure of tartaric acid in the grape. This is the measurement of how acidic the wine will taste. Any number too high and the wine will taste sour. If the TA is too low the wine will feel flat and watery on your pallet.
For premium wines, a grower might also consider the amount of anthocyanin (color compound) in the wine. Additionally, some aroma compounds deteriorate with ripeness, such as green bell pepper or fresh cut grass aromas. Growers need to wait till these smells break down, otherwise you and I will be able to smell it in the final product and most consumers don’t really want to drink grass.
-Brian Tomasello 4th Generation Outer Coastal Plain Winemaker Tomasello Winery