when to harvest grapes

Grapes across California are beginning to reach their sweet, delicious peak, sending harvest 2016 into action across the Golden State. As the wild crescendo of the season nears, it’s all about waiting for the perfect moment to pick, and in a state with 918,000 acres under vine, that’s a lot of waiting and watching.

The waiting doesn’t just buy winemakers an extra week of summer vacation, but the chance for truly exceptional wines. Especially in sunny regions like California, the trick to a successful harvest (and resulting amazing wine) is picking grapes at their ideal ripeness, not simply when they taste sweet. Through the weeks leading up to harvest, vintners carefully and continuously test their vineyards and plan the ideal moment to harvest the fruits of their summer’s labor. Wine is all about balance, and winemakers look for the perfect balance between flavor components like sugar, acid, and tannin. Unlike simple table grapes, wine grapes need more than just sugar to make great wine.

Sugar molecules are fuel for fermentation, and more sugar means more potential alcohol. In warm New World climates like California or Australia, full ripeness allows red wines to be so juicy and high in alcohol that the wines can easily reach 15 or 16 percent ABV. There are many ways to measure sugar (including the good ‘ole taste test) but In the US, sugar is measured in brix, a scientific measure of the percentage of sugar in a liquid, and thus the potential alcohol of a wine. Depending on the style of wine to be produced — white or red, robust or light — winemakers look for a readings between 22 and 26 brix. Compared with table grapes, which have an average brix of 18, ripe wine grapes are incredibly sweet.

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But sugar isn’t the only quality that makes a grape wine-ready. Without sugar’s partner in crime, acid, vino becomes dull and flabby instead of delicious and refreshing. Acids found naturally in fruit balance the sweetness of sugar, like a perfect yin-yang of flavor. While many wines don’t seem sour, even reds naturally include some these grape acids, which allow wine to pair well with foods and taste crisp and bright. As berries swell with sugary juice, acids dissipate, so winemakers keep a close eye on the correlation between pH and brix to harvest at the ideal acid-sugar ratio. In general, wine grapes are harvested when their pH is between three and four, or roughly as tart as Sour Patch Kids candy. Like Sour Patch Kids, wine grapes are intensely sweet and powerfully tart at optimal ripeness and, compared with table grapes, they’re still exceedingly bitter.

The bitterness quotient of wine grapes comes from their thicker skins and the seeds that most table grapes don’t have. Adolescent grape berries contain bitter green seeds, which develop inside the grape as the season progresses. As bunches mature and change color, the green grape stems also get ready to abandon their branches, drying up and turning brown. When the stems have browned, the seeds inside the grape have also matured from bitter and green to crisp, brown, and filled with tannins and the polyphenols that make red wine heart-healthy. Now, instead of adding unpleasant green flavors (think stewed bell peppers or compost) these seeds contribute tannins that make red wine a great pairing for fatty meats, and help vino age for decades.

Together, the sugar-acid-tannin trifecta makes wine grapes ready to leave the vine and head to the presses, starting the second half of their journey to liquid gold. While California is still in the throes of drought, waiting and watching gives winemakers the potential for beautiful, multifaceted wines. With harvest, Mother Nature passes the baton to winemakers, and the next leg of the race from field to glass continues.