What is whole-cluster fermentation? How does it affect the wine?

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Dear Dr. Vinny,

Could you please shed some light on whole-cluster fermentation? We encountered this on a visit to Willamette Valley, where many of the Pinot Noir producers seem to employ it. Yet most in Sonoma seem to avoid it.

—John and Joyce, Castle Rock, Colo.

Dear John and Joyce,

Sure thing—here's the whole story! Whole-cluster fermentation is just what it sounds like: The whole grape cluster is harvested off the vine and then crushed and fermented, stems and all. (The more popular alternative is to remove the individual grape berries from the clusters and discard the stems before crushing and fermentation.)

I’ve mostly seen whole-cluster fermentations employed with Pinot Noir and Syrah grapes, and it's not an all-or-nothing proposition—a winemaker might choose to just throw in a few whole clusters with the rest of the destemmed grapes, or go all in with 100 percent whole clusters (my impression is that whole-cluster fermentations tend to employ about 20 percent to 40 percent whole clusters).

So what's the difference between a wine fermented with whole clusters (stems and seeds included) vs. the more conventional destemmed method? Stems impart their own unique flavors, as well as more tannins and structure. How well this works depends on how ripe the stems get. I know that might sound weird, but when grapes are picked early, the stems can still be green and rubbery, and those underripe stems bring more green, vegetal and herbal notes. Leave the grapes on the vine for a while longer and the stems lignify, or turn brown and woody, and the flavors they add turn a bit more mellow and spicy, more toward black tea, floral or forest floor notes.

I’ve also seen firsthand how the stem inclusion can add more structure and muscle to a wine, though those who aren’t fans would call the influence astringent or coarse. Stems can also absorb pigments, lightening the color of the wine.

Some winemakers claim that stems help enable the fermentation process itself, facilitating the success of the yeasts and allowing for small levels of carbonic maceration to take place. In a true carbonic maceration, whole grape clusters are tossed into a tank that’s then sealed, and the lack of oxygen and all of that trapped carbon dioxide allows for the grapes to ferment inside their skins, keeping the flavors fruity and the tannins light. Whole-bunch fermentation doesn’t necessarily mean that the winemaker is sealing the tank, but I’m sure you can imagine how some of those bunches stuck on the bottom under the weight of all the other grapes might spontaneously generate a little carbonic maceration.

If it sounds like I’m a fan of whole-bunch fermentation, I am. In the right hands, in the right vintage, with the perfect amount, I can really pick out this note of peppery freshness, particularly in my Pinot Noirs. But I also love plenty of wines that don’t employ any whole bunches, and it’s never been a deciding factor in picking out a wine for me, just a note that I can appreciate.

Whole-cluster fermentation isn’t an Oregon vs. Sonoma thing. These conversations are happening all over the world, and every winemaker has to make the decision that’s best for them. Many who employ whole bunch, particularly with their Pinot Noirs, point to influences from Burgundy, but not every Burgundian winemaker uses the method.

—Dr. Vinny

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