Does Coffee Go Bad?
One question that's relatively common -- especially if you're an infrequent coffee drinker, or if you were a bit overzealous because it was on sale -- is, "Does coffee go bad?" The answer is, yes, it does. Okay, our work here is done.
Wait, you wanted to learn more? Here's how to tell if coffee has gone bad, and why freshness matters.
There's no such thing as a coffee molecule. Coffee -- whether it exists in bean or ground form, or it's sitting in front of you in a cup -- is made up of as many as a thousand different compounds, including carbohydrates, amino acids, and lipids. With the passage of time, those compounds undergo physical and chemical changes that alter the aroma and taste of both the raw material and the finished product. Carbs go stale, lipids go rancid, volatile organic compounds evaporate, and other components change with exposure to oxygen (oxidation) or water. Even small changes can have a significant impact on the taste of your coffee.
How long your coffee will last depends on its form, as well as where and how it's stored. If taste is your concern, your best bet is to store coffee in an airtight container somewhere cool, dry, and dark. Stored this way, ground coffee can be used for a few months past its expiration date, whole bean for up to nine months, and instant coffee for up to twenty years. You can also store coffee in the freezer, which greatly extends its shelf life (anywhere from one to three years for whole bean and ground coffee, and practically indefinitely for instant). However, freezing coffee practically destroys its flavor; the more interesting parts of the flavor profile vanish, and coffee that's thawed from frozen will taste dull.
Peak flavor can vary, depending on the type of beans, the roast, and the brewing method used. In all cases, however, your safest bet is to use coffee as close to the roasting date (not the expiration date) as possible. Often, the expiration date is a year from the date on which the beans were roasted. The closer you are to the latter than the former, the less fresh (and less tasty) the coffee. If you've bought coffee and you're not sure when you'll use it, as happens if you usually drink regular but keep a can of decaf onhand for company, at least keep it sealed 'til you're ready to use it. Most coffees are packed with nitrogen to slow spoilage, but once the seal is broken, you're trading nitrogen for oxygen and humidity, both of which rob your coffee of flavor. Since the preceding sounds a bit confusing (and Googling returns all sorts of contradictory information), let's distill this to its essence.
Fresh coffee is best, period. Freshly ground coffee, if you have the beans and a grinder; as close as possible to the date of purchase if you've bought your coffee pre-ground. If it looks or smells a bit "off" (rancid, moldy, or mildewy), throw it out. If it just smells flat, it's going to taste flat, since the smell of coffee is such an important part of its flavor profile. Unless it's gone moldy, you shouldn't get sick from expired coffee, but just because you can drink coffee that's past its expiration date doesn't mean that it's a good idea. Freshness matters!