The twin myths of “easier to extract” and “overextraction”
There are a few common utterances about coffee that perplex me. One is blaming “overextraction” for bitter or astringent brews, despite their extraction levels not being high. The other is calling some coffees “easy to extract” despite their not producing particularly high extraction levels.
Overextraction doesn’t exist
Unless you are Nestle or some sophisticated operation hydrolyzing cellulose to achieve extractions of 40—50%, I doubt you have ever “overextracted” a coffee. When baristas refer to overextraction, they almost always mean a coffee was astringent due to channeling.
“Overextracted” implies an extraction was higher than optimal. But the term is thrown around without evidence that an extraction was, in fact, too high.
Let’s take a specific example: A barista brews a v60 and enjoys it. On the next brew, he or she makes the grind a bit finer, finds the result astringent, and declares it “overextracted.” There a few problems with this:
There is no evidence that a higher extraction was the problem. Even if extraction was measured and found to be higher, that is not evidence that higher extraction was the problem; that is simply a correlation.
The finer grind may have produced a lower extraction due to some combination of clumped grounds or channeling
The barista has not properly tested whether a higher extraction could taste better if, for example, he or she had used a better technique or different recipe.
I’ve witnessed many baristas achieve very low extractions and declare a brew “overextracted.” Yet I’ve had brilliant, non-astringent brews as high as 28—29% EY (extraction yield) using the NextLevel Pulsar and the “blooming espresso’ recipe on the Decent Espresso Machine. If those extraction levels are possible, then a typical v60 or espresso with 20% EY is unlikely to be “overextracted.”
The myth of “easier to extract”
I scratch my head every time I hear a barista say a coffee is “easy to extract.” I don’t know what that means. My guess is it’s a poor way of communicating “this coffee tastes good almost no matter how I extract it.” If that’s the case, the more accurate statement would be “this is a high quality coffee.” Great coffee may taste good even when extractions are not optimal.
Much like with “overextraction,” “easy to extract” is usually claimed with no reference to actual extraction levels. “Easy to extract” should imply that a coffee achieves high extractions. In my experience, many Kenyan, Ethiopoian, and a few other select, superior green coffees tend to extract higher than other coffees. Those are, indeed, easy to extract, but not usually what baristas mean when using the phrase.
Most baristas tend to believe dark roasts are “easy to extract,” but even that supposition is suspect. Light-medium roasts seem to achieve the highest extraction levels. Underdeveloped roasts yield the lowest extractions, presumably due to low porosity within the cellulose. Extraction potential seems to peak at a light-medium roast level. Darker roasts often extract a bit lower, presumably due to some soluble material burning off during the roasting process, resulting in a higher proportion of insoluble material. I don’t have precise color readings to offer yet, but this trend seems to hold across high-quality arabica beans.
I’ve heard baristas refer to certain coffees as “difficult to extract” but that may simply mean “difficult to make taste good using my usual methods.” In that case, the culprit may be a roast problem, low-quality green, or some mismatch between a coffee and a barista’s brewing decisions (for example, grinding too fine and causing clumping in the coffee bed, which leads to water channeling around the clumps.) But it is unlikely the coffee is, in fact, difficult to extract, unless the roast is genuinely underdeveloped.