Pre-ground coffee can be bought from many places, even supermarkets. If you don’t have a coffee grinder at home then there is nothing wrong with buying pre-ground coffee however it does affect the quality of the final product. Not only will the coffee go stale a lot quicker, but if the coffee it produces isn’t good quality then you cannot adjust the size of the grind to suit your needs.
We recommend that you buy and use whole beans for all brewing methods and then grind only enough for what you need each time. For commercial use, most grinders will have a hopper to store the whole beans so that coffee can be ground fresh every time you need a shot pulled.