What do "reductive" and "oxidative" mean?

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Dear Dr. Vinny,

I currently go to school for enology and viticulture. There has been some confusion between myself and other students regarding the labels of "reductive" and "oxidative." What exactly do they both mean, and what is the science behind them both? We often do blind tastings and these become very valuable descriptors, however, I must admit that I'm not as sure about the meaning as I could be.

—Janna S., Walla Walla, Wash.

Dear Janna,

These are complex questions, and your professors will surely have more comprehensive answers than I can provide here. So do your homework!

To start off, "reductive" and "oxidative" are terms to describe winemaking styles, not wines themselves. Traditional winemaking is considered oxidative, meaning that the wines are exposed to air (in open-top fermentors, for example, or during racking). Reductive winemaking takes extra steps to conduct winemaking in the relative absence of oxygen. It may sound kind of crazy, because air is everywhere. But by using stainless steel tanks and inert gases, a winemaker can greatly reduce the exposure a wine has to oxygen. The intent of reductive winemaking is to maximize the fresh fruit flavors in a wine.

In a blind tasting, you won't necessarily be able to pick up on what kind of winemaking style was used, but you might notice "reduced" or "oxidized" notes. (Reduced notes are often the result of reductive winemaking, but oxidized notes aren't necessarily the result of oxidative winemaking.)

"Reduced" notes generally result from the present of volatile sulfur compounds, or mercaptans; these notes include rotten eggs, rubber, struck matches, sewage and even skunk. There can be a beautiful wine underneath the reductive notes, and sometimes—not always—decanting or vigorous swirling can help these notes blow off. Reduced notes have also been linked to screwcapped wines (another situation where a wine has limited exposure to air), though my own observations of this link are rather inconclusive.

"Oxidized" notes appear when a wine has had too much oxygen exposure—more than it would get through traditional oxidative winemaking. The fresh fruit flavors are faded, the wine takes on nutty notes, like a bruised apple, its color starts to fade and it might remind you of Sherry. I often describe oxidized wines as tasting "tired," and indeed, many past-their-prime wines have oxidized notes.

—Dr. Vinny

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