More than anything else, extraction determines how good your brew is going to be. Understand it, and you’ll be well on your way to an amazing cup.
Extraction describes the process of pulling flavor from each speck of ground coffee. It’s the reason the water goes in clear and comes out brown: As it passes through the grounds, it’s dissolving all kinds of compounds and taking them straight into your cup. Here’s the tricky part: Some of those compounds taste great, but others are kind of nasty. To get the good ones, and the right amount of them, you need to properly extract your coffee, meaning that the water dissolves the right stuff, and the right amount of it.
Too little, and your coffee is under-extracted; too much and it’s over-extracted.