By Nick Pratt
I decided to try Matt's experiment while pulling shots of last month’s reserve coffee, Victoria Champila. This is a light roast, making it particularly challenging to dial in the shots, but why not try it out? I used 21 grams of coffee for each shot, with the “correct” shot weighing 32 grams for a 25 seconds extraction. That’s a 1:1.5 yield, which is usually my target for a regular shot. The point of the experiment is to taste espresso shots with different extractions but the same strength.
Stop here for a second.
If you don’t know the difference between extraction and strength, please do a little reading. In short, espresso extraction measures "what" from the grounds makes it into your cup, and strength measures "how much" of that stuff is in your cup. With drip coffee, we have full control of both strength and extraction. It’s totally possible to brew an under-extracted and weak cup of coffee by manipulating the grind and dose. With espresso, strong = under-extracted and weak = over-extracted*.
In this experiment, we take shots with different extractions and dilute them with water to the same strength. This allows us to taste the extraction without being confused by strength. As an analogy, imagine tasting different brands of vanilla extract. Most likely, there's one you like best, but the flavor is so strong you’ll never be able to tell, unless you dilute it. The same applies here — the under-extracted shots are so strong that you won’t get much information, unless you water them down. You’re not changing what the flavor is, just how strong the flavor is. Get it?
We pulled 7 shots from strongest and most under-extracted to weakest and most over-extracted. (There’s a “cowculator” on Matt Perger’s site that explains how to extract and dilute the shots.) The under-extracted and strong shots were smaller, so we diluted them to equal the same strength as the weaker, over-extracted, larger shots. Shot 1 was the smallest and most diluted, shot 2 was a little larger and less diluted, shot 3 was larger and less diluted than 2, etc., until shot 7, which wasn’t diluted at all. The procedural stuff is a little monotonous, but the tasting afterwards is what really mattered.
The very diluted shot 1 was so much more telling than tasting that shot undiluted (which I did before the experiment). You can really taste how sour the espresso is when you are not overwhelmed by the strength. Each shot was less and less sour until shot 4, where it was well balanced. Shot 5 was also good, just a little more bitter. By the time I got to shot 6, we were definitely into the over-extracted/bitter range, and shot 7 was unpalatable.... That’s when I realized what this exercise can be used for.
This experiment is great in two ways — it teaches you about espresso extraction and it teaches you about a specific coffee as espresso. The first part, teaching about extraction, is something I’m going to use with students when we’re talking about how to taste over/under extraction. It’s going to be a lot of fun. The second part, teaching about a specific coffee, is something I’m going to use every time I dial in a new coffee. Maybe just pulling shots and making adjustments can get you close, but diluting a few shots that are close to your target would tell the full story.
So what did I learn?
I already knew how espresso extracts, but that was a good refresher. However, I also learned that my 32 gram shot of espresso could potentially improve if it were 35 grams. I pulled that shot again at 35 grams in 26 seconds and it was noticeably more balanced.
Better espresso through science? Check.
*This statement is not 100% true. You can pull an over-extracted and strong shot of espresso with some tweaks of your grind. The same is true for under-extracted and weak. However, this is not the normal circumstance when pulling shots.