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Dear Dr. Vinny,
During fermentation, when the grape skins and other bits rise to the top, is it best to leave it be? Or should it be pushed back down into the fermenting juice?
—Frank, Windsor, Ontario, Canada
While grape juice is fermenting, those bits of grape stems, seeds, skins and pulp that float to the top are referred to as the “cap.” Why does it float? One of the byproducts of the fermentation process is carbon dioxide gas, and as it escapes, those solids rise with it to the top. Those solids in the cap also happen to contain most of the polyphenols that give wine its color, aroma and body, so if you want a full-flavored wine, you should definitely punch down the cap to extract those elements. If you leave the cap untouched, it can also become a breeding ground for bacteria, so that’s another good reason to keep things circulating!
There are two primary methods of extraction: Punch-downs (also know by the French term pigéage) and pump-overs (aka rémontage), and they’re pretty much exactly what they sound like. A punch-down can be done by hand using a huge potato masher–looking device, by foot (preferably with the assistance of waterproof waders), or by machine. Breaking up and submerging that cap usually requires a lot more force than you’d think. A pump-over typically involves pumping juice up from the bottom of the tank and splashing it over the cap. As you might imagine, both of these methods (and how forcefully and frequently they’re performed) have a big effect on how much pigment, tannins and flavor are extracted. These are some big decisions.
Another method, not so common, is called “rack and return.” (“Racking” is a fairly common practice for removing fermented wine off of the sediment, or lees, to clarify it.) This, too, is pretty much exactly what it sounds like: The wine is drained into a second tank, leaving the solids behind, and then returned to the original tank with the grape solids. It’s kind of like an extreme pump-over.
Eventually, when all the punch-downs and pump-overs are complete and the fermented wine is removed from the tanks, the solids left behind are known as pomace, and there’s some pretty cool stuff you can do with that, too!
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