Why You Shouldn't Grind Coffee Beans Too Far In Advance
You've got the expensive coffee machine, the right beans, and the perfect roast, but you still can't achieve the ideal coffeehouse flavor that you're looking for. This is because a ton of factors influence the taste of the coffee. Yes, all the items mentioned above are important, but so are the grind size, water to coffee ratio, roast date, and a slew of other things. While it's near impossible to nail down exactly what that missing element is without practice and experience, the process of grinding beans is something many home brewers overlook.
Most grounds are stored in airtight packaging that keeps them from getting too stale, and coffee grounds will only lose so much flavor in storage. However, from the moment the beans are ground, they begin to release flavors and oils that will be missing from the final brew (via Coffee Bean). Here's what you should avoid doing to preserve as much of the coffee beans' original flavors as possible.
Grinding too early subtracts from coffee's flavor
Easy Home Coffee notes that an easy way to understand this is to think of why we grind coffee beans in the first place. Grinding beans creates a larger surface for water to come into contact with and draws out the desired flavors. The same goes for when coffee is exposed to air. When there is more surface area exposed, then more of the coffee's flavor — and especially aromas — can be extracted. The purpose of grinding coffee is to unlock all of those flavors trapped on the inside of the bean. Once they are exposed to the air though, they begin to oxidize (a fancy word for going stale) and leave you with less to extract when you brew.
The easiest way to fix this is to wait until you're ready to brew for any grinding. It is always important to store your coffee — ground or not — in an airtight container, in a cool, dark place (via National Coffee Association). Also, for all that is caffeinated, keep them out of your refrigerator and freezer, or they might adopt the flavors of whatever else you're storing