The decision on when to pick wine grapes comes down to two very important things: chemistry and intuition!
There are some tell-tale signs that the grapes are ready for harvest, including their color and their flavor. Red grape varietals will turn from green to red, but true ripeness may take weeks to set in once the color turns. But did you know that grapes are easier to pull from a cluster when they’re ripe? They plump as sugars increase and release easily, hinting that they’re ready to start their journey into the wine bottle. The color of the stems and seeds will also turn brown when the grapes are ripe.
One of the most important metrics we use during harvest is Brix, the determination of how much sugar is in a grape. We can use instruments to measure how much light passes through a sample; liquids containing sugar are denser than water and cause greater light refraction. We measure Brix to calculate the potential alcohol strength of the finished product. At 24 Brix, a wine should be between 13.5% and 14% ABV after fermentation. Picking grapes at 20 Brix is undesirable because the ABV would only be 11%, but picking them at 30 Brix would result in a wine with 19% alcohol strength. We also focus on acidity, which can be measured in TA (titratable acid). This metric gives a good indication of how sharp the wine tastes on the tongue, or how much acid you perceive when you taste it.
If all the numbers look good, we do a taste test! Even if all the metrics align, the grapes may not taste fully developed. If there’s no complex flavor and we just taste sugar, water, and acid, we’ll let them hang longer to develop more. We harvested our viognier pretty late this year because it didn’t taste perfect even when the Brix was high. The longer we leave the grapes on the vine, the longer they have to develop flavor to become a better wine. With viognier, we aim to make a rich, fruity wine that is medium- to high-bodied. On the other hand, we picked our sauvignon blanc earlier because we wanted it to be more acidic. Everything has been harvested now except cabernet franc, cabernet sauvignon, petit verdot, and riesling!
