The short answer is no, dry coffee beans can't go bad, as in: they are shelf stable and they won't make you sick when you make coffee from them, even if they're very old.
If the beans get wet, or if you have wet coffee grounds, then you should definitely toss them, as they will eventually start to grow mold.
But the long answer (there's always a long answer) is that roasted coffee beans can go stale and the resulting brewed coffee or espresso will be not be at their optimum flavor. Always buy coffee that has a "roasted on" date, so you have a real idea of how fresh your beans are.
How to keep your coffee as delicious as possible? Keep these factors in mind when storing your coffee beans:
Oxygen: store your beans in an airtight container, as oxygen quickly degrades their flavor.
Light: Coffee stored in glass containers is beautiful, but light also degrades your beans, so an opaque container, or a clear one that you keep in a cabinet away from the light, is preferable.
Heat: Now that your coffee is in an airtight, opaque container, make sure it isn't over the oven or any other warm place, like a kitchen counter that gets lots of sun.
Moisture: unless you're actually pulling a shot of espresso or brewing a batch of coffee, keep it away from water.
Storing your coffee in the freezer isn't really necessary unless you have more coffee than you think you can get through in a couple of weeks. Freezing coffee will not magically turn old beans into fresh beans, unfortunately, so if you already have some coffee you know is starting to stale, you can't "save" it by freezing it.
Since it's an immersion brewing method, it won't have those bright flavors you get out of a shot of espresso or a batch of pour over- instead, you'll get a smoother, low-acid, but highly concentrated, coffee. It's a different animal, but if you have some extra beans kicking around, it's a nice way to use them up.
Basic Cold Brew
170g (6 ounces) whole coffee beans, coarsely ground
1020g (36 ounces) cold water
8 to 12 hours of your time
- In a large container, combine the ground coffee with the cold water and stir to evenly saturate the grounds. Cover and let infuse for 8 to 12 hours at room temperature.
- Strain the concentrate with a fine mesh strainer or a coffee filter, then transfer to an airtight container and refrigerate until completely chilled.
- To serve, pour over ice and dilute (this is the important part) to taste with water, milk, or a non-dairy alternative of your choosing. Add sweetener to your preference.
You can also use cold brew to make:
Rich Coffee Syrup
1 cup sugar
1 cup undiluted cold brew coffee (at room temperature)
- Stir until the sugar dissolves and store in an airtight container, refrigerated, for up to a month.
Use coffee syrup drizzled over a cake or some ice cream, or anywhere you might use maple syrup. Or use it for a cocktail- Coffee Bourbon Old Fashioned, anyone?