The recipe says to stir less if the coffee tastes over-extracted and to stir more if it tastes under-Extracted. Is this different from stonger and weaker? What does extraction taste like?
Yes, over- and underextracted are quite different from weak or strong coffee. The strength is determined by the amount of grounds, more grounds = stronger coffee. But that’s not what your recipe is talking about.
Preparing coffee is a physical and chemical process (although some aficionados will claim that it’s an art) where soluble compounds (“flavors”) are dissolved in water. The coffee bean contains various compounds that dissolve at different speeds, with acidic flavors being quickest and bitter notes, e.g. tannins slowest.
Without going into the details:
- An under-extracted coffee will be acidic, and missing the “fullness” from the coffee oils.
- In a just right extraction, acidity will be a side note to a full body of coffee oils and sugars with a bit of bitterness for balance.
- An over-extracted coffee will be unpleasantly bitter, masking the desired flavors, and sometimes even with an astringent mouthfeel.
The beans, roast, grind size and brewing method are all parameters that influence the ratio of aromatic compounds and/or rate of extraction, but the principle described above remains. clive Coffee has a neat blogpost on the topic and there’s even a Wikipedia article on coffee extraction.