An unopened liquor can keep for years, and is indeed intended to remain stable for decades if necessary, although there is no further aging once the spirit is removed from its oak barrel, unlike wine, which continues to improve. Once the bottle is opened, however, new rules apply. Neutral spirits — those, such as vodka, that don’t contain added flavors or sugars — will prove more robust and fare better than others, but experts recommend keeping an opened bottle no longer than a year. Since U.S. regulations require spirit bottles to list alcohol content but not necessarily use by date, certain rules of thumb are the best guidelines.

Short Life Span

Liqueurs, which contain cream or eggs, such as Irish Cream or advocaat, need to be consumed within a few months of opening, although manufacturers typically set 30 months as a recommended limit. While the alcohol content will inhibit aging, the dairy products will eventually curdle, particularly if the bottle is kept in a warm environment. Cream liqueurs are among the few spirits to come with a use by date and readily announce themselves when spoiled. In some cases, the liquid may even solidify, but a foul stench will usually deter even the most optimistic drinker.

Long Stretch

The higher the alcohol content in a bottled spirit, the longer will be the shelf life. Generally, an alcohol content of 17 percent or above will preserve the contents indefinitely. The sugars, however, will react over time and can form a crust around the bottleneck and cap; this might attract undesirables such as ants and flies. High proof whiskey, vodka, rum and vodka will keep for years and withstand warm conditions much better. Rum, after all, is a child of the sweltering tropics. However, drinkable does not automatically equate with good to drink. A liquor that has been kept too long will have few qualities left to savor.

The Effects

Although the enduring myth is that liquor has a limitless shelf life, spirits kept in an opened bottle will start to oxidize at around the six- to eight-month mark. Another deterioration, particularly if conditions are warm, is that the alcohol will gradually evaporate, leaving a product that is insipid and a pale imitation of its former glory. Similarly, bottles containing a low level of liquid will stand up worse than fuller bottles. For cherished liquors, such as vintage single malts, transfer remaining liquid to a smaller bottle or flask as soon as possible.

Storage Tips

Unlike wine bottles, which should be stored sideways to stop the cork drying out, spirit bottles should be kept upright; otherwise, the higher acidic content will eat away at the stopper and facilitate oxidation. An increasingly common trick is to keep spirits, particularly vodka, in a freezer. The alcohol content prevents the liquid from freezing and results in a smooth, somewhat oily consistency when poured. Cream liqueurs should be kept refrigerated after opening, and consumed within six months at best.