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!

16 Responses to Yield vs. Strength vs. Ratio

  1. Mike White says:

    Thanks Nick, you’ve summarized nicely what I’ve been coming to grips with myself. This is very helpful.

  2. Michael Walcher says:

    ughhhh head aslpode.

  3. Chris Capell says:

    Nice summary, Nick. I was lucky enough to have Scott Rao walk me through all this; otherwise it’s not immediately evident, so this is very helpful.

    One humble suggestion — I would summarize strength as ‘how concentrated is the cup?’ Maybe it’s just how my brain works, but I’d answer your questions like this:

    “How much did you get from the grounds?”

    “20%”

    “How much ended up in the cup?”

    “All of it, I didn’t spill any.”

    :-)

  4. Chauncey says:

    Great explanation as usual, Nick. My copy of Scott Rao’s latest arrived today so looking into going even further down the rabbit hole of extraction times, dosage, when to stir and how much,e tc.

    I’ve been all over the solution/suspension and TDS thing ever since you explained it to me back in the Murky days. I keep reading that the SCAA TDS meter (using conductivity) that was the standard just a couple years ago has been abandoned in favor of Brix/refractomer readings because the readings were off by 30%. When you are dealing with a target range of 18-22% extraction, accuracy at every stage seems critical.

    MojoToGo is indeed an awesome tool. I wish I could spring for the meter or there was a cheaper “pro-sumer” version to bring the whole package under $100. When you buy almost 100 bucks of pricey beans a month, you want each batch to be magnificent.

  5. [...] MoJoToGo has made its debut appearances on Sprudge (here and here), has been further debated on Portafilter.net courtesy of Nick Cho, and Mike White has been charting his progress over on ShotZombies (here and [...]

  6. Marcus Young says:

    Nice summary. I’ve listened to and talked at length with Vince at VST about all of this and appreciate your accurate yet simplified explaination. Your post will be a great resource to point wholesale clients to before I descend on them to check extraction. Sweet!

  7. I started thinking about coffee this way after doing the SCAE gold cup course with Paul Stack and Mike Khan.

    Generally I approach brewing now with the strength of the cup in mind first. I tend to assume that I am aiming for a very narrow band of extraction (19-20%) so strength and ratio have a fairly linear relationship for me.

    If a coffee has great body and mouthfeel then I might want to emphasise that with a slightly higher dose, a consistent extraction/yield and thus a slightly stronger cup.

    On the note of doses – I can’t state enough how important an exact weight is in single cup brewing. Bulk brewing has the luxury of wider tolerances (in terms of grams or fractions thereof) as being 2g is a smaller error in terms of % of the dose in a 110g dose compared to a 15g dose.

    Weighing before and after grinding for single cup brewing and using the mojo is v v important. A little sloppiness has a surprisingly large impact in the cup.

  8. Jason Dominy says:

    Very good thoughts. As someone who’s been working with the Extract MoJo lately, I need all the help I can get understanding this side of coffee better.

  9. Aaron Frey says:

    Makes me want to buy a refractometer now… Thanks for posting, helps clarify some of the blogging people are doing while tinkering with their Mojos (hah).

  10. Nate says:

    A year ago, when I started learning more about coffee, little did I know just how little I knew! The more I learn, the more I learn I need to learn more. Does that make any sense? Anyway, I enjoyed this post very much. There are so many factors that must be accounted for to properly brew coffee, yet %90 of coffee drinkers are slinging back cups of rancid sludge. Thank you for contributing to my coffee education!

  11. Matt Flipago says:

    This chart makes it seem like it’s imposable to get weak underdeveloped and bitter coffee.

  12. coffee girl says:

    Very interesting. Thanks for the good information!

  13. Nick Cho says:

    @Matt Flipago: Sure you can. Just brew really un-evenly. Pour or spray your water only on the left-half of the grounds… you’ll have some nice mix of over and under extraction.

  14. Andy Berard says:

    Thanks for the awesome clarification on porta filter brew strength as I will share this formula with our customers. There is always a confusion in relation to how much product used to obtain perfect extraction. Great advice.

  15. Daniel says:

    Great explanation of this important coffee concept.

  16. Brian C says:

    I have always heard 33% for total extractable solids from coffee from the SCAA. Where can I find data on the 27-30% that you cite here?

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