Why Grind Size Matters?
Grind size effects 3 factors in coffee: contact time, extraction time, and flow rate.
The more surface area on the coffee bean, or how fine it is, the more exposure it has to water. And that water exposure decides everything.
The more surfaces that interact with water the less time it needs to be there (contact time). The more surface area to interact with water means the less time is needed for the water to extract components (extraction time).
Finally, grind size determines how fast, or slow, the coffee can physically move through the grounds (flow rate).
What This Means Is:
- The finer the beans are ground, the higher the extraction rate is and the less contact time is needed.
- Alternatively, the courser the beans are ground, the less surface is exposed, which means a slower extraction rate, therefore, more contact time is needed.
- The finer the grind, the slower the water can move through it. The courser the grind, the faster it can go through.
All of this is a long way of saying that if your brew method has a short contact time (like espresso), the grind size should be finer. If your brew method has a long contact time (like French Press) the grind size should be courser.