Updated: Jul 4, 2020
Deciding when to pick grapes for wine can be challenging. There are many factors involved, but luckily two of the most important are easy to measure; sugar and acid. As the harvest approaches, sugar levels will increase, while acids will decrease to a manageable level. If you are lucky, sugar and acid will be where you want them both at the same time. If you are not so lucky, you can try to get as close as possible while minimizing trade offs. Depending on the variety that you are growing, the optimal sugar and acid levels will vary. This article is intended to provide some target numbers to get you into the ballpark for each popular grape variety.
At Harvest vs At Bottling:
The pH will generally rise .15 to .3 during primary fermentation and malolactic fermentation. To achieve the target balance at the time of bottling, the grapes will need to be picked with a bit more acid to compensate for this loss.
Grapes will be picked with very high sugar levels, but this does not mean they will be sweet. For a dry wine, nearly all of this sugar is converted to alcohol. More sugar means more alcohol. If you know the target alcohol number, divide it by .57 to get an estimate of the percent sugar needed to achieve the target.
Targets vs Reality
The targets provided are a great starting point if you are unfamiliar with the variety. There are great wines that are made outside of these target windows though. The winemaker style and the climate are driving factors that would lead one to make a wine that doesn't meet the norm for that varietal.
Target Values for Red Wines:
Harvest pH 3.3-3.4, 24-26.5° Brix, .6-.7 TA
Final pH 3.6-3.7
Harvest pH 3.2-3.4, 23-25.5° Brix, .65-.8 TA
Final pH 3.55-3.65