TDS and the control chart

Strength and extraction are different axes, and confusing them is the most common dead end in brewing. Strength — measured as TDS, total dissolved solids — is how concentrated the drink is: what percent of the liquid in your cup is coffee rather than water. Filter coffee lives around 1.15 to 1.45 percent TDS; espresso runs 8 to 12. Extraction yield, from the last lesson, is how much of the grounds dissolved. A cup can be strong yet under-extracted, or weak yet over-extracted — and each combination has a different fix.

Strength is water math: change the ratio or dilute. Extraction is technique: change grind, temperature, time, or evenness. Two axes, two steering wheels.