During the month of June, the grapevine berries have formed and are beginning to grow. This critical time in the development of the vine is called fruit set of the grapes. The below photo gallery shows fruit set grape images from the 2016 vintage.
Fruit set happens at slightly different times for white grapes and red grapes. The temperature of the wine region also plays a factor. For Jordan, chardonnay grapes grown in the cooler Russian River Valley tend to flower and set fruit in mid-May, around the same time that our merlot grapes flower in the warmer Alexander Valley. Cabernet sauvignon is a later-ripening grape variety and typically doesn’t flower until 2-4 weeks after early-ripening grapes.
The flowering of grapevines in the spring determines the number of berries that form, or fruit set. Without consistent, moderate weather during flowering, also known as bloom, grape flowers cannot turn into berries and have what farmers call a great “set.” What winemakers and grape growers hope Mother Nature will deliver every May is moderately warm days with very little wind, no rain and no heat spikes. In years like 2012 and 2013, they get their wish for both early- and late-ripening white and red grapes. But in years like 2016, chardonnay, merlot and other early-ripening varieties didn’t have a great fruit set because of inclement weather during flowering. When May weather is a mix of cool days, rain showers and even heat waves, the bloom of grapevines will be uneven–some flowers won’t even pollinate–leading to less berries per cluster of fruit. But this transition from flowering to fruit set determines quantity, not quality. In 2016, chardonnay grape growers were not 30 percent down like they were in 2015 for cabernet sauvignon–it was closer to 15-20 percent less–which isn’t too bad. Meanwhile, late-ripening cabernet sauvignon enjoyed a normal-to-above-normal sized crop in 2016, as summer weather returned to wine country in late May. With a few chardonnay clusters in these fruit set grapes photos, you’ll also see examples of what we call “hens and chicks,” where the grapes grow at different sizes due to inconsistent flowering times. You’ll also notice that a handful of the grape flowers that didn’t turn into berries are visible in the bottom-left photo.
Once the fruit sets, it goes through rapid cell development, expanding in size. Before the end of July, red wine grapes will begin to change color, the next step in the life cycle of the grapevine called veraison. Geek out on fruit set in the vineyard with our other wine 101 blog.