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Dear Dr. Vinny,
How are wines filtered?
—Jeri Sue H., Deming, N.M.
Dear Jeri Sue,
There are four different methods winemakers use to clarify a wine. That means removing sediment—dead yeast cells and bits of grapes. This is done not only for cosmetic reasons (vintners generally prefer clear wine to murky wine), but also to protect against a wine re-fermenting in the bottle. Other winemakers like to leave all that stuff in there, feeling it adds to the texture and flavor of a wine.
The first method is racking, and it’s the most unobtrusive way. You move wine from one barrel to another, but as you do so, you leave the last bit of wine in the first barrel where all the sediment has settled.
You can also filter the wine, using various filter pads or membranes, which trap the sediment. There’s also a process called fining, where you add something that binds to the sediment—typically a type of protein, such as egg whites. The fining agents coagulate with the sediment, making them bigger and therefore easier to trap in a filter, or to leave at the bottom of a barrel if you rack again. (The fining agent is not meant to remain present in the finished, bottled wine.)
The last method is cold stabilization, and that’s meant to avoid those crunchy bits of tartaric acid that look like rock candy or shards of glass. They’re harmless, but can be annoying. The wine is chilled severely, and then the crystals are removed so you don’t have to deal with them.
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