Oxidization: Wine's Worst Enemy

  By far the most common problem with home made wine is simple oxidation. This occurs when the wine is allowed too much exposure to the air. There are some simple ways to avoid oxidation, but to understand the problem better, let's first look at what it is, how it effects your wine, and why it often goes undetected.

  Undetected? Unfortunately, yes. Oxidization, as stated above, occurs when the wine is allowed too much exposure to the air. This allows free oxygen molecules to combine with wine molecules, forming a new molecule (like rusting metal), which is essentially the oxidization, since the new molecule accounts for the change in taste and colour in the wine. This is most easily recognizable as an orange to brown tint in red wine, noticeable around edges of the wine in a glass, and a brownish tinge to white wines. Taste is a more subjective thing, but many liken it to an acidic, metallic taste.

  All wine kits come with an anti-oxidant package, usually potassium metabisulphite, which is added at the stabilizing stage. This works by combining with the free oxygen molecules before they affect the wine, and creates a harmless compound which falls out as sediment. The anti-oxidant we add is not limitless, however, and can only absorb so much oxygen. Think of it like batteries. The more you have to use it, the quicker it will run out. Wines subject to too much exposure to air during the winemaking process will use up all the anti-oxidant quickly, and will therefore start to oxidize sooner than well made wines. Such wines, with which extra care and attention was taken during the winemaking process, will have a much longer shelf-life in the bottle, allowing the wine to go through the full maturation process before deteriorating.

CAUSES:

  Firstly, when using a two stage, primary/secondary fermentation, failing to transfer the wine from the primary to secondary at the right time is a very common mistake. Although wine kit instructions generally say transfer on day 7, the wine absolutely must be transferred while actively fermenting. If the temperature is on the warm side, or if the wine is left longer than intended. and it finishes fermenting in the bucket, it will start to oxidize immediately, and any subsequent racking will worsen the problem, even though the unsuspecting winemaker is just following instructions.

  Secondly, excessive racking will cause oxidization. Some winemakers prefer to rack their wine four or five times instead of filtering it, in the belief that this will clear the wine. The best way to clear a wine without filtering is to leave it sit in the carboy, with fining agents and stabilizers  added, in a cool place for as long as possible. Don't rack it back and forth, this causes oxidization!

  Thirdly, some winemakers still don't add the anti-oxidant at all, in the mistaken belief that "chemical-free" wine is better.

  Want a quick idea of what oxidized wine tastes like? Just pour a glass of wine and leave it on the kitchen counter for 24 hours. Then taste it every day or so until you can't stand it anymore. That's a speeded-up version of the oxidization process, easily avoided with a few simple precautions.