The "right" grind
If you want to enjoy your coffee to its full advantage and allow the (desired) aromas to develop, you need to use the “right” grind for your preparation method.
Coffee beans contain a total of over 1000 aromatic compounds. Only about a fifth to a quarter of these aromas are actually contained in your finished coffee or espresso. In order to get the “right” aromas in the “right” proportions for your coffee speciality, you have to create the optimal conditions. This sounds more complicated than it really is. If the water is relatively soft (e.g. low in lime) and the brewing temperature is within the correct limits, all you need to do is to create the right ratio between the grind and the amount of time the coffee is contact with the water.
If the coffee beans are ground too coarsely and not allowed to spend enough time in contact with the brewing water, specialists talk of under-extraction. Under-extracted coffee tastes watery, bland and often sour.
This is due to the fact that acidic flavouring agents dissolve more easily and quickly than the flavours which give coffee its body and a fuller taste. In addition, most "sweet" aromas require a slightly longer extraction time.
Coffee beans that are ground too finely and left in contact with the brewing water for too long results in a bitter, harsh-tasting coffee with an unpleasant mouthfeel. The proportion of dark, woody and burnt aromas also increases. Here we are now talking about over-extraction.
An example of this is when coffee beans that have been ground for espresso preparation are prepared in a French press instead. The finely ground coffee (small particles, overall large surface area) are covered with water and "floated" (full immersion) and left to steep for 3-4 minutes.
Your guiding principle should therefore be: the less time the coffee comes into contact with water, the finer the grind should be.
(Of course there are also exceptions to this rule, such as when preparing mocha.)
To simplify our examples, we use a scale from 1 to 10, where 1 is the finest possible grind and 10 is the coarsest possible grind. This classification only reflects our experience with our own coffees.
Fine grinds (levels 1 to 4)
Level 1:
Mocha/Turkish mocha
Levels 2-4:
Espresso machine: short contact time, high pressure and high temperature
Second compartment of fully automatic machines
Hand filters, such as permanent filters, Hario, etc. (finer for paper filters, coarser for porcelain filters)
Medium grinds (levels 5 to 7)
Levels 4-6:
Hand filters (finer for paper filters, coarser for porcelain filters)
Levels 4-5:
Aerospress
Chemex
Stufe 6-7:
Espresso pot / stovetop pot / screw pot
coffee filter machine
Coarse grinds (levels 8 to 10)
Level 8:
Coffee siphon
French press / bistro jug / Bodum jug
Level 9:
Karlsbad style pot
cold brew preparation