Knowing the optimum time to pick your grapes for wine is a crucial skill that must be mastered before any vineyard can become successful, yet the “knowing when” seems to be the one thing that eludes many amateur vintners.
What’s At Stake
The timing of the harvest plays a serious roll in the resulting wine. Basic features such as flavor, acidity, body, color, as well as stability are all tied to this decision. One should think of the harvest timing as the first decision to be made in the wine making process.
Grapes are no different than most fruits on the face of this earth. As they mature through the growing season, they go from small and tart to big and sweet. In general, we want the grapes to be as sweet as possible but without risking the loss of too much acidity or acidic strength.
The sugars are what the yeast ferment into alcohol. The more sugars there are in the grape juice the more alcohol you will have from the fermentation, so we always want more sugar. But we also don’t want the acidic concentration and strength to deplete too much. This will cause the wine to be less stable and less likely to be able to protect itself from flavor deterioration, loss of color intensity, and potentially spoilage. We also don’t want the wine to be too acidic. This will make the wine too tart or sharp in flavor.
As a vintner there are three key pieces of equipment that are necessary to determine the when to pick your grapes: a refractometer, an acid titration kit, and a pH meter. Refractometers measure the amount of sugar in the juice. An acid titration kit measures the amount of the acid in a juice. The pH meter measures the strength of the acid in the grape juice.
I would also strongly recommend getting a wine hydrometer for doing a final check of sugar levels before actually picking the grapes. The hydrometer actually floats in the juice to determine the Brix level. Having a wine hydrometer will also be handy later on when you’re actually making the wine.
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years. #picking