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Why do wines go bad?
How Wine is Made

Why do wines go bad?

Consider a wine that has been opened versus one that has not. A wine that has been opened typically spoils within a day or two of being uncorked. However, an unopened bottle of wine can last hundreds of years if it is processed and stored correctly. Regardless of the reason, if you do not like the wine, do not feel obligated to drink it. Even if a wine has not “gone bad,” you should enjoy the wine you’re drinking.

How Wine is Made

When understanding why a wine might go bad, understanding how wine is made is important. Wine is produced from fermenting grape juice with yeast. The yeast eats the sugars in the grapes, producing alcohol as a by-product. Outside of the wine-making process, these sugars typically cause grapes to spoil. However, once those sugars are processed into alcohol, wine can be shelf-stable for many years.

Whether stored in a cask or a bottle, take care to prevent the wine from being exposed to air. In a bottle, a moist cork is inserted into the neck of the bottle. If the cork dries out, it can shrink, allowing air in. The wood expands when in contact with the wine in a cask, creating an airtight and liquid-tight vessel.

If air is introduced to the bottle of wine, it could react with the alcohols in the wine to create acetic acid or vinegar. Bacteria in the air could also start growing in the wine. Between the oxidation and the bacteria, the wine will develop a vinegar-like flavor that is undesirable.

This is why a bottle of wine goes bad quickly after it has been opened. To keep your wine fresh, consider using a wine preservative, such as a can of compressed gas that can be sprayed in the bottle to displace the oxygen or a vacuum sealer that removes the oxygen. However, these methods only slightly extend the length of time you could enjoy your bottle.

Very rarely, a high-quality bottle of wine may be corked with a natural cork that is infected with a fungus. This fungus grows naturally on the cork oak tree, from which corks for wine bottles are harvested. This fungus could ruin a bottle of wine. However, only about 5-10% of all wines are spoiled by this fungus. Despite this, natural cork is still preferred, especially for high-quality wines. However, many wines are corked with synthetic corks, which are not susceptible to the same fungus.

The color of wine typically deepens with age, but the color can also indicate if a wine has spoiled. While good quality wines can last hundreds of years in storage, even improving with age, low-quality wines may spoil. Winemakers may age the wine in casks or barrels that prevent light penetration, which can spoil the wine. However, wines that are stored in bottles are typically stored in colored glass that can prevent some light from penetrating through. Light can degrade components of wine, such as antioxidants and tannins. Antioxidants can keep the wine from oxidizing, and oxidation causes acetic acid to build up in the wine.

Additionally, the tannins that exist naturally in grapes help to give the wine its unique flavor. When light hits the tannins, they start to degrade, which can negatively impact the flavor. Bottled wine at home should be kept away from strong light. This is why wine cellars are usually dark, such as a windowless room or an underground cellar.

Another reason a wine may go bad is from a process called secondary fermentation after the wine is bottled. The remaining yeast in the wine may consume additional sugars, which can impact the flavor. Wines that have undergone secondary fermentation may be carbonated or sparkling when they shouldn’t be. Carbonation happens when the yeast consumes sugars and produces alcohol, as well as carbon dioxide, that cannot escape the airtight bottle. This carbon dioxide gets dissolved in the wine, producing bubbles.

Carbonation may indicate that an undesirable yeast or bacteria has stayed in the wine after fermentation or bottling. If you open a bottle that fizzles when it shouldn’t, it has likely spoiled. Sometimes, other bacteria could cause your wine to taste bad or feel weird in your mouth. Slimy textures, bitterness not typical of the type of wine, or a smell of rotten vegetables or earthiness may be indications that you should discard the bottle. These bacteria are rarely found in commercially produced wine.

High-temperature swings can also spoil a wine. In the same way light can break down tannins in a wine, so can heat. Heat will cause your wine to age much more quickly than if it is stored at recommended temperatures, ideally between 53-57F. The flavors of some wines might improve with age, but aging wine through heat can have unpredictable results. It is generally recommended that wine not be stored above 75F for more than a few days or above 80F for more than a few hours.

Temperature swings can shrink and contract the cork, resulting in a leaky bottle of wine. If the cork has bulged from the neck of the bottle or wine has seeped up the sides of the cork, the wine has likely spoiled.

To summarize, the most common way for a wine to go “bad” is when oxygen has been introduced to the bottle. To keep your wine from oxidizing or breaking down, try to store your wine properly in a cool place and away from direct light. Enjoy your wine within a day or two for the best experience. Always remember, if the wine does not taste right, do not feel obligated to drink it.