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Have you ever opened a bottle of wine then left it unsealed for a little too long?
You return later to pour another glass and discover that it is now slightly brown, stale, and has a tangy, metallic smell. That is a case of the chemical reaction called wine oxidation.
Air mixing with wine can have a detrimental effect on a wine's chemical makeup. You may have to toss out your favorite bottle because the air has turned it from sweet to bitter. Even worse cases of oxidation can destroy whole batches of wine due to errors made during the fermenting process or when trying to age wine.
Oxidation isn't always a bad thing for wine. Winemakers often use it intentionally to draw out flavors in the wine. This is how some winemakers achieve deep, rich, earthy tones in their wines. Oxidation also plays a major part in optimizing the taste of a red wine or port when you choose to use a wine aerator or wine decanter (see also: what does a wine aerator do).
Wine Oxidation Chemistry
Oxidation in wine is a chemical reaction that occurs when the oxygen in air comes into contact with the alcohol in wine. The two elements react and cause the alcohol to convert into acetaldehyde. Acetaldehyde is an organic chemical compound that naturally occurs in fruits, breads, coffee, and wine. This is the source of the flatness and sour flavor that develops in an oxidized wine. Metabolizing these foods also causes the creation of acetaldehyde in the human body.
Given enough time, the acetaldehyde can further convert into acetic acid. This is not the normal kind of acid in wine. Acetic acid will take you from wine to vinegar. And that's exactly how you end up with white and red wine vinegar (see: red wine vinegar vs white wine vinegar). This shows how drastic of a chemical effect oxygen has on alcohol over time. Limiting exposure is paramount in preventing the chemical changes of wine oxidation. You can read all about the chemistry of wine if you pick up one of the best wine books available.
Can You Drink Oxidized Wine?
Yes, you can drink oxidized wine. It’s not dangerous to consume, it just has an unpleasant taste. Drinking oxidized wine is no different from consuming flat soda or stale bread. The chemical makeup has altered slightly, but there are no compounds added that would prevent you from being able to drink a glass. Studies have also shown that acetaldehyde naturally breaks down in the human body without adverse effects. The only benefit of oxidized wine is that the lowered alcohol content may also lower the calories in wine.
Don't expect to enjoy the taste. The metallic taste of the oxidation will outweigh the taste of the sugar in wine. Your best bet is to toss the wine and get a new bottle. Oxidized wine isn't even worth using as a cooking wine due to the diminished alcohol content.
Is Oxidized Wine Bad for You?
No, there are no known issues that arise from drinking oxidized wine. Though acetaldehyde is considered a toxin, the low levels found in an oxidized wine are not dangerous to consume. Drinking oxidized wine is similar to drinking vinegar. It's not going to damage your body, but it tastes harsh.
There is some evidence that acetaldehyde contributes to the feeling of a hangover after drinking. You may be at increased risk of a hangover from drinking oxidized wine. The wine will certainly not be enjoyable to drink, but it is unlikely that you will get sick from doing so. The wine alcohol content will also be lower due to the conversion of ethanol to acetaldehyde. It may also be safer for people who have wine allergies, but it's better to avoid.
How to Fix Oxidized Wine
Depending on how oxidized wine is, you may be able to halt wine oxidation in winemaking using powdered skim milk. A simple mistake in brewing can cause your mixture to take on a brown hue or make the taste metallic. If caught early, you can introduce another substance to stabilize the mixture. This won't reverse the oxidation but may keep the wine from becoming undrinkable. For each liter of wine, add 1/2 ml powdered skim milk and 5 ml of cold water. Stir the wine and continue the process. It will be about two weeks until the final product is ready.
Unfortunately, some oxidized wines are too far gone to save. Correcting wine oxidation is a complicated matter. If you're looking to correct oxidation in a drinking wine you purchased for consumption, you're out of luck. Pick up a new bottle and make sure to follow the proper wine storage procedures. Light, heat, and air are capable of ruining your favorite wine. Storing the wine for a few weeks can also help prevent a run-in with bottle shock in wine. Getting the best wine cellar app can help with these storage issues.
How to Keep Wine From Oxidizing
The best way to keep wine from oxidizing is to limit the amount of contact the wine has with air. Keep wine sealed unless you are intending to drink the wine in that sitting. Even resealing an open wine will not stop the oxidation process. Have you ever put a stopper in a bottle and tossed it back in the fridge? You've probably found that the taste is much worse the next time you open the wine bottle. That's because the oxidized layer of wine continues to convert additional alcohol within the bottle. This is the same for all wine bottle sizes.
If you are a home winemaker, make sure to keep your wine airtight and clear and stabilize your wine on schedule. You don't want to introduce air unless you know how to intentionally oxidize wine to achieve certainly flavor profiles. Oxidation during fermentation even affects the tannins in wine, so your red wine can actually turn out to be a brown vinegar.
Instead of preventing oxidation, you can intentionally limit the oxidation wine to achieve greater depth. You should make sure you know what you’re doing if you’re going to attempt it so you don’t ruin the wine. Learning how to aerate wine and how to decant wine can really change how you drink your favorite beverage.
The Bitter Truth About Oxidation
Oxidation is inevitable in wine. Every time you open a bottle, air begins to work on transforming your wine into a new substance. Make sure to handle the wine properly if you don't want to waste any. Even freezing wine won't stave off oxidation for long. Don't waste a great wine varietal by leaving it exposed.
If you're making your own wine, try to keep on schedule and avoid exposing your creation to air when not necessary. There are methods to save the wine, but it will never be as flavorful as it would be without wine oxidation. You can even bring it out to a restaurant and drink your un-oxidized wine if you're okay with paying a corkage fee.
The way oxygen changes the makeup of wine is used intentionally in oxygen-based stain removers. These removers break down the set-in wine so it can be blotted away. You can learn more about this by reading how to remove red wine stains or about the best wine stain removers.