Ground coffee beans flying from a coffee grinder
Food - Drink
Why You Shouldn't Grind Coffee Beans Too Far In Advance
Many home brewers often overlook the process of grinding beans when trying to achieve the ideal, coffeehouse-style cup of coffee. From the moment the beans are ground, they begin to release flavors and oils that will be missing from the final brew if the grinding isn’t done at the right time.
The purpose of grinding coffee is to expose more surface area of the beans to the water, so that more of the coffee's flavor — and especially aromas — can be extracted. Once the ground beans are exposed to the air though, they begin to oxidize, or turn stale, and leave you with less to extract when you brew.
The easiest way to fix this is to hold off the grinding until you're ready to brew. It is always important to store your coffee — ground or not — in an airtight container, in a cool, dark place. Also, keep beans out of your refrigerator and freezer, or they might adopt the flavors of whatever else you're storing.