Alcohol Won't Expire, But That Doesn't Mean It's Automatically Safe From Other Threats
Alcohol is great at doing many things: being paired with food to elevate it, making people fun at parties, making other people not fun at parties, and causing severe liver damage. It's also great at killing dangerous microorganisms like salmonella and E. coli, a trait that has important implications for the culinary and medical industries. Alcohol denatures (breaks down) the proteins within germ cells, causing them to lose their structure. The protective cell membranes dissipate, killing them. It's the same chemical process behind soap. Thanks to this effect, alcohol can be used to protect our food, as well as our bodies themselves, from potentially harmful infections.
You can't use every alcoholic beverage as a disinfectant or in food preservation. Pouring White Claw on a cut won't do you much good because it takes 80-proof alcohol (40% ABV) to guarantee that no bacteria can survive. That happens to be a standard proof level for vodka, gin, whiskey, and rum, which can serve the same bacteria-killing purpose in foods. Peaches in brandy, plums in whiskey, and citrus in vodka are examples of such. Still, the best-known example of preserving food in alcohol is probably vanilla, the pods of which are submerged in rum, which eventually turns the liquid into vanilla extract. Since spirits of 80-proof and up can preserve other foods, it should be no surprise that the drink itself will never expire, but that doesn't mean it can't go bad in other ways.
How alcohol can spoil
Alcohol does not expire in the way other beverages and foods do, in that it never becomes unsafe to drink. That's one of the main reasons alcohol became popular in the first place; in the days before refrigeration, alcohol could be safely stored for years on end. The only real threats to the beverage come after it's been opened, at which point fruit flies may infest it, or, in rare cases, the liquid can evaporate. And yet, alcohol can still be said to spoil in its own unique way, as age can change a liquor's flavor and aroma. This occurs when the alcohol has prolonged exposure to light, heat, or oxygen.
When you leave a bottle of alcohol open for a long time, it can oxidize, causing changes in the flavor profile that range from subtle to severe based on the type of liquor and your palate. Certain alcoholic beverages are more vulnerable to spoilage than others, with stronger spirits generally faring better. Pathogens can infect beer unless it is pasteurized, and wine will gradually turn into vinegar in the event of prolonged oxidation. For the most part, you don't need to worry about getting sick from expired alcohol. Still, your drink will likely become weaker in taste and alcohol content since heat can cause alcohol to evaporate into the air. Fortunately, it's easy to avoid these pitfalls if you store your liquor properly.
How to maximize your liquor's shelf life
The most important thing to consider regarding the shelf life of alcohol is when you open the bottle. An unopened liquor bottle has an indefinite shelf life, but once you pop the top, oxidation and evaporation begin to take their toll. That said, it's best not to open any liquor bottle unless you can see yourself using it within 6-8 months. It should retain its optimal flavor for at least that long. The alcohols most vulnerable to spoilage are liqueurs and cordials because they tend to contain large amounts of sugar.
The spirit with the most staying power by far is vodka, which isn't surprising since, in addition to its high ABV, it has little-to-no flavor. An open bottle of vodka could theoretically last for 50 or even 100 years before all its alcohol evaporated.The alcohols most vulnerable to spoilage are liqueurs and cordials because they tend to contain large amounts of sugar. The less sugar in your alcohol, the longer it will last.
It's vital that you properly store your liquor, especially after it's been opened. Keep it in a cool, dark place. You can keep it in the freezer since 80-proof spirits have a freezing point of around -16 degrees Fahrenheit, well below the zero-degree level most freezers sit at. You also need to store it in a bottle with a tight seal, i.e., a screw cap. Corks are not as secure and could still expose the alcohol to air.