Extraction
What is extraction in coffee?
Extraction is the process of water dissolving flavour compounds out of ground coffee. Under-extracted coffee tastes sour and thin; over-extracted coffee tastes bitter and dry. The SCA guideline for filter coffee is an extraction yield of roughly 18–22%.
Grind size, water temperature, contact time and agitation are the main levers that control extraction. Finer grind, hotter water, longer time and more agitation all increase it.