Foundational

Extraction basics

What extraction means, and how under- and over-extraction each taste.

Three labelled panels in a row — under-extracted, balanced and over-extracted — with the balanced panel highlighted in the middle and an arrow beneath showing extraction increasing to the right. — Illustration, not a photograph. The taste descriptions are typical rather than certain — temperature, freshness, roast level and dose can each push a cup sour or bitter too.

What extraction is

Extraction refers to how much of the soluble material in ground coffee is dissolved into the water during brewing. Different flavour compounds dissolve at different rates, which is why brew time, grind size, temperature and ratio all interact.

Under-extraction

Under-extracted coffee often tastes sour, thin or salty, because primarily the fast-dissolving compounds have come out while sweeter and more balanced compounds have not yet been extracted.

Over-extraction

Over-extracted coffee often tastes bitter, harsh or hollow, because slower-dissolving, more bitter compounds have been pulled out in excess relative to the sweeter compounds.

Using this to troubleshoot

Tasting for sourness versus bitterness is a practical first step in diagnosing most brewing problems, before changing grind, ratio or temperature. Extraction is not the only possible cause of either, though — water temperature, bean freshness, roast level and dose can each independently push a cup sour or bitter even at a reasonable extraction level, and more than one factor can be involved at once. See the dedicated troubleshooting pages for sour and bitter coffee for the fuller set of likely causes, not just the extraction-only explanation.

Sources

SCA brewing and espresso standards — Specialty Coffee Association (SCA)