An introduction to understand how grind size impacts your cup of coffee.
The grind size of coffee is one of many factors that affect the flavor of your cup of coffee. The variance in flavor when brewing coffee is based off many factors, including: water temperature, pressure of extraction, surface area of the coffee grinds, method of brewing, and so on. If you are trying to brew the perfect shot of espresso, the grind size needs to be fine, given the amount of pressure necessary to extract the shot. For instance, when using a coarse coffee grind when pulling an espresso shot, the result is faster extraction of the espresso for there is little to no pressure.
The lack of pressure when making a pour-over or V60 allows for more coarse coffee grounds by comparison. This takes away ‘pressure’ as a variable when making drip coffee. Practicality is in play, where using a paper filter introduces the need to brew more coarse coffee grind to allow for the water to permeate through and extract the coffee drink. When paper filters are used with a fine coffee grind, the result is often a more bitter flavor profile due to overextraction. The longer the water sits in the coffee grounds, the more overextraction occurs. Such is the case when water is introduced to more surface area of coffee grounds.
Another case of overextraction results when brewing fine ground coffee using the French Press. If we were to look at two samples of coffee grinds, one very fine and one very coarse, intuitively we are able to tell that the sample of the fine coffee grounds has more surface area for the water to extract coffee, during the brewing process, than the coarse grind. This is all to say that grind size is connected to how your cup of coffee will taste, with overextraction being a culprit for bitter and harsh flavors of coffee.