I bought a new coffee maker and it has a permanent filter and says to only use filter ground coffee.What exactly is filter ground coffee?
Filter ground coffee stands for roasted, then cracked to smaller pieces to be brewed easily coffee beans. The question is, how small and consistent you should crack them to pieces. This is important as it affects the extraction of the coffee, so your cup. You should crack all the coffee beans at the same desired size for a good cup of coffee.
Here's a previous discussion on a similar topic, but on espresso machines:
And, what about the right size? It should be about 400 microns for a drip machine that uses filter size grounds. But, don't worry. Coffee shops know about these. All you need to do is just ask for it or read the labels. Here is a quick chart for all coffee brewing methods and ground sizes:
Filter ground coffee is simply coffee which has been ground to a particular size, namely for the method of drip-/filter-/pour-over coffee.
Different brewing methods require different grind sizes. To categorize it roughly. From small to large with the smallest size (extra fine) corresponding to a flour like texture and the largest size (extra coarse) corresponding to crushed pepper:
- Extra fine: Turkish coffee
- Fine: Espresso or Mokka/stove-top coffee (most pre-ground coffee is this size)
- Medium-Fine: Filter coffee such as V60/Kalita or AeroPress
- Medium: Filter coffee such as Chemex/Clever Dripper or Filter coffee such as V60/Kalita or AeroPress
- Medium-coarse: Filter coffee such as Chemex or Batch Brewers such as Mokkamaster or AeroPress
- Coarse: French Press or AeroPress
- Extra coarse: Cold brew maybe in Toddy systems or maybe cowboy coffee and similar things.
As you can see these categories are not fixed, since grind size is only one of many variables that influence the coffee extraction (among them time and temperature). The AeroPress exemplifies that best as you can vary the grind size significantly and still produce balanced cups, although with different flavor focuses depending on the grind size. For paper filter systems depending on the system you should not grind to fine since the paper gets clocked and the coffee doesn't drain properly anymore. Similarly don't grind to large as the water would flow through to quickly.
For you the most relevant will be medium-fine to medium grinds as that will be the size commonly sold as filter grind in supermarkets. In a specialized coffee shop the size they will grind you their coffee to (if you buy it there) may differ from that in supermarkets, but they will usually give you recommendations and tips on how to use it with your specific filter coffee machine. Depending on which one you have, a medium-coarse grind might produce better results. Although that is likely not what they mean when they write filter ground coffee, if it is a common household machine from a standard home appliances store.