Yield vs. Strength vs. Ratio
A semi-quick post about filter coffee brewing and measurements. I’ve been seeing some Twitter activity from both ExtractMojo’ed and not-yet-Mojo’ed folks, who are exploring metrics related to brewing.
There are a shit-load of variables to wrap your brain around, but on the analyzing-the-resultant-brew side of things, three big ones pop out: Yield, Strength, and Ratio.
If you’ve ever looked at the good ol’ Brewing Control Chart and been a little confused, or never bothered to look at it too closely, it’s about damn time that you did.
It really boils down to three questions:
1) Yield = How much did you get from the grounds?
2) Strength = How much ended up in the cup?
3) Ratio = How did you get there?
Yield: Yield pertains to how much soluble you took from the coffee grounds. Ground coffee has something between 27-30% of its mass being soluble, that is, stuff you can dissolve in water. If you kept boiling and boiling coffee grounds in water, eventually you’d get everything that the grounds have to give. Above 22-24%, however, and you’ve essentially reached too far or squeezed too hard, because unpleasant flavors will emerge. Below 18%, and you’re not getting enough out of the coffee, at worst, leaving the coffee with underdeveloped flavors or simply wasting coffee. So it sort of answers the question, “How much did you get from the grounds?”
Strength: Pertains to how much of the final brew is coffee, and how much is water. SCAA Golden Cup says 1.15-1.35% brew strength is a desirable zone to the most number of people, though we espresso-lovers tend to like a bit more… something like 1.3-1.5% brew strength. Over 1.5, up to 2.0% or more, and you’re in the “heavy, thick” coffee zone. Simply put,“How much ended up in the cup?”
Ratio: Simply, grams per liter. It provides one of the major answers to the question that Yield and Strength might ask, that is, “How did you get there?” Perhaps the most easy-to-remember ratio is 60g/L, or 60 grams of coffee for every one liter of water. The fact that you can make a balanced, pleasing, delicious cup of coffee at 60 g/L should give any barista pause when they’re finding that they’re using 80 grams or more per liter when they’re making coffee. Is it “wrong” to make coffee at 90 g/L? No… but is the additional 50% of coffee yielding an additional 50% of coffee quality, compared to the barista down the street making superb coffee at 60 g/L?
This triumvirate: Yield, Strength, and Ratio, give you a hell of a lot of information. Ratio is relatively easy to calculate. For Strength, you need to measure the TDS somehow. The most ghetto way of doing this would be to make a shitload of the coffee you want to measure, boil off all of the water, and weigh the resulting coffee dust… but just get a TDS meter, okay?
Yield is calculated by knowing the other stuff. Basically, if you know how much your resultant brew weighs, and you (with your trusty TDS meter) know what percentage of it is coffee solubles, then you can calculate how much mass of coffee soluble you have. If you then divide that by the mass of the coffee you started out with, then you’ve got Yield! There are ways of skipping having to do the math.
Now there’s a shitload more stuff to consider, but these are the main ones. Keep in mind that this all makes sense and will correlate to cup quality only when all of the other variables are optimal. Good quality coffee, “proper” water, temperature, even extraction, etc. With manual coffee brewing techniques, that last one is a tough one… but that’s a blog for another day.
Only recently has this whole Yield vs. Strength vs. Ratio thing “clicked” in my brain and made some useful sense. I’ve gotten quite a few emails and messages over the past few weeks asking about brewing and how it relates to something like ExtractMojo. Hope this was helpful!
Note: if you ever see a brewing control chart like the one above, and “1.00″ has “1000″ next to it, the “1000″ is missing a zero. 1,000 TDS = 1,000 ppm (parts per million) = 1,000/1,000,000 = 1/1,000 = 0.1%. Watch out for typos, kids!