Measuring Coffee Extraction, and Why it Makes People Mad
Coffee people get mad about extraction yield. Just uttering the words can cause a fight. Why? For years, the topic has been somewhat weaponized by coffee bros[i] — relegated to arcane forums, referenced in heated comments sections, and heavily gatekept to those simply curious to learn more.
The messaging has been abysmal: “If you don’t know your coffee’s TDS and EXT% you’re incompetent and your coffee is trash.”
Meanwhile, it’s nearly impossible to find clear information about what TDS and EXT% even are. So, if you’ve approached this article with hesitance, that is very understandable! And I’d like to assure you that I’m just here to provide information free of judgement.
Why do I care? Because I am a small business owner and I care about small businesses. A working knowledge of extraction yield is really, actually, sincerely an invaluable operations tool for coffee businesses, and it can save you money. You can lower your costs by consuming less, a winning scenario for both the environment and the economic sustainability of your business. And as I write this, during the coronavirus pandemic, many coffee businesses are tackling existential crises head on and I want this to be another tool at your disposal. If your company brews and sells coffee in any way, including bottled coffee, this tool can help you!
I’m writing this for every coffee professional who’s felt annoyed, left out, or judged when trying to learn about extraction yield. No matter what any coffee bro says, it’s a straightforward, easily understood concept that can help your business. And after you read this, I hope you’ll look back and laugh in disbelief that this subject matter was ever controversial!
Note: if you already know exactly how extraction yield works, but you want to learn about the money part — skip to the section titled This is It! This is the Money Part! Ok let’s get this show on the road.
What is Extraction Yield?
What is coffee flavor made of? A lot of acids. Also: oils, plant fiber, carbohydrates, caffeine, and over 1,000 aromatic compounds.
When we brew coffee, we use water as a solvent to remove flavor solids from coffee grounds. The solids are then suspended in the solvent, and that’s the beverage we call coffee. But — particularly in specialty coffee — we don’t usually try to extract the full 30% of soluble content. Why? Because not all of those solids taste delicious.
The yummy solids dissolve pretty easily during brewing. But if we keep extracting, we eventually get harsh, muddy, woody flavors. So, in specialty coffee, we just want to extract the sweetest, fruitiest parts and then stop. This is usually around the 20% mark.
When we talk about how many coffee solids are dissolved during brewing, that’s extraction yield. Extraction yield is typically expressed as a percentage and abbreviated as EXT or EXT%. I don’t know if this needs to be said but you can only measure EXT% after you’ve brewed the coffee.
“What’s the EXT% on this pourover, do you reckon?”
“That there pourover is a 20% EXT, pardner.”
I don’t know why these baristas are cowboys but I don’t know why not either. Now let’s get along, little doggies, and talk about WHY THE HECK ANYONE CARES.
Why the Heck Anyone Cares
Generally speaking, the more you extract coffee, the tastier it gets — up to a point. We’ll call it The Point. After The Point, extraction starts to taste harsh, woody, muddy. The trick is to extract as much as you can before the coffee hits The Point.
This also is my opinion: there’s a lot of underextracted coffee in the world. It’s very easy to underextract. A lot of coffee recipes set parameters for low extraction. Baristas dialing in at cafes are more likely to prefer the flavors of underextraction (sour, dilute) to overextraction (harsh, bitter). Roasting issues can cause underextraction. It’s just very easy.
Unless you’re actively focused on optimizing solids yield, there’s a chance that your coffee may be a little underextracted. Why does that matter? It doesn’t have to, if you don’t want it to.
But this is also my opinion: many specialty coffee businesses can improve quality and save a good amount of money by increasing their extraction yields.
We’ll talk more about the money part soon. Right now, let’s discuss how we figure out an extraction yield. To start, we need to know the coffee’s TDS.
What Is TDS?
Coffee with a lower proportion of dissolved solids tastes weaker — it’s less concentrated. Coffee with a higher proportion tastes stronger — it’s more concentrated. Espresso is extremely strong because it’s extremely concentrated. It contains about 10% solids, a much higher concentration than regular drip.
In other words, the strength — or concentration — of brewed coffee depends on its number of Total Dissolved Solids — or TDS.
“Howdy, ranger. What’s the TDS of that there pourover?”
“I reckon that’s a 1.25% TDS.”
Yes, we’re still using cowboys in these examples.
Anyway, the more solids you extract from your coffee grounds, the more solids end up in your cup. However — and this is important! — solids aren’t the whole deal.
What is the Whole Deal?
Just because you have a lot of solids, that doesn’t mean the coffee is strong! Because you could also have a lot of water! So the solids get diluted in all that water! High TDS doesn’t necessarily mean high EXT%!
How is this possible?
Think of your coffee grounds like a brand new, totally full container of cocoa powder. You decide to make hot chocolate. And how much cocoa you take from the container, that’s like the EXT%.
Then you mix that tiny spoon of cocoa powder with just a bit of water.
The resulting hot chocolate is concentrated. It’s strong. It has a high proportion of solids to water. That’s a high TDS. And that is how you can have a high TDS but a low EXT%.
You don’t need to memorize this, just think of it like hot cocoa and you’ll remember. Low TDS + high EXT% is like emptying the whole container of cocoa — but mixing it into a bathtub of water. High TDS + high EXT% and low TDS + low EXT% are also possible and can also be explained with the hot cocoa analogy.
Also like, obviously I don’t actually make cocoa with water, I make it with milk or nondairy milk because I prefer a rich creamy mouthfeel. But here’s the big question: how do we know the number of solids in a cup of coffee? Do we, like … count them?
Kind of! TDS is measured with a handheld instrument called a refractometer. Refractometers shoot a laser through a small coffee sample, measure the degree to which the light changes direction, and convert that into your TDS reading.
Coffee refractometers are simple to use; however, the pricing starts at $250. So the investment makes more sense for professional use rather than home use. Quick tip: the most popular model of refractometer, which costs $950, is not a must-have. The cheaper model works fine.
Once you have a refractometer, you can read your coffee’s TDS. And knowing TDS will allow you to calculate EXT%.
The Incredibly Complicated Mystery Equation
We want to know how many coffee solids — by weight — moved from the grounds to the brew. In order to calculate this, we need to know three weights.
- The first weight we need: the grounds. This is very easy — just weigh the dry coffee grounds on a scale. Write down the weight in grams.
This one is a little harder because brewed coffee is made of both water and solids — so how do we separate solids weight from water weight? We look at our TDS reading from the refractometer! The reading tells us, in a percentage, how much of the brew is solids.
To get your EXT%, just divide the weight of coffee solids by the weight of grounds. In other words:
(TDS * brewed coffee weight) / coffee grounds weight = EXT%
Got it? Now some fine tuning! Typically, roasted coffee has about a 3% moisture content, and CO2 makes up around 0.5% of the weight. So you want to account for this when you write down your grounds weight. The actual grounds weight is the weight on your scale, minus moisture and CO2.
Most of us don’t have the instrumentation to measure our coffee’s CO2 and water content, so coffee pros typically sub in 3% for water content and 0.5% for CO2 content. With those approximations, your equation will look like this:
(TDS * brewed coffee weight) / (coffee grounds weight — [3.5% * coffee grounds weight]) = EXT%
I personally put the equation into a Google spreadsheet and keep a shortcut to it on my phone. I open the sheet just like I open an app, input my three weights just like in an app, and the spreadsheet automatically calculates EXT% — just like an app.
This is It! This is Where You Find Out How to Save Money!
Let’s say we have 1 kilogram of roasted coffee beans (one kilo is 2.2 lbs or 1,000 grams).
We want to brew some coffee with this kilo of beans. That means we want to extract solids from the beans and mix those solids with water. We’re going to sell this brew — this mixture of solids and water — in 300 ml servings. And we want each serving to have a 1.5% TDS. That means that each serving will contain 4.5 grams of coffee solids and the rest is water.
If we extract 15% of that kilo, we will yield a total of 150g of coffee solids. That’s the amount of solids only, not water. 4.5g of solids are required per 300ml serving — that creates a 1.5% strength. So we have enough total solids for 33 servings of coffee.
Not bad! But let’s take it up a notch and extract 20% of that kilo, instead of 15%. At 20%, we will yield a total of 200g of coffee solids. That is enough for 44 servings of coffee.
That’s 33% more cups of coffee. At the same strength and using the same amount of coffee beans.
And in case this isn’t obvious, 33% more cups of coffee is 33% more revenue. Without increasing costs.
Ok, we’ve got the solids part. But coffee is solids and water, both. So now let’s talk about the water.
When we brew 20% EXT instead of 15% EXT, we yield more solids — so we need more brew water for those solids. Once we add more water to the recipe, we have enough liquid volume to fill those extra cups while keeping the TDS steady at 1.5%.
But how do we *magically* get a 20% extraction instead of 15%? Incidentally, adding more brew water is also one of the easiest ways to increase extraction yield.
The less coffee to water you have, the higher your extraction yield. Why? A few reasons. For one, a large coffee bed is harder for brew water to evenly saturate, so a higher proportion of coffee to water can impede extraction.
Secondly — especially when dealing with immersion brew methods like the French Press — your brew water can only extract so many solids. It will eventually reach a saturation point and become less efficient as a solvent. A high proportion of coffee to water means the water becomes saturated before it can extract a high percentage of the available solids. So that’s why you can extract more by using more water.
When dialing in your coffee-to-water ratio for high extraction, I recommend starting with one-part coffee to 16 parts water. The 1:15 — 1:17 range usually works best. (Note: I don’t know if this needs to be said but I’m saying it. Using less coffee has the same effect on extraction as using more water.)
More Ways to Increase Extraction
High extraction, by my definition, is anything upward of 20%. But not every coffee tastes good in that range (roast is a big factor here). If you want to brew for high extraction, always use your palate to guide you because the numbers alone are not enough. The trick is to extract as many tasty solids as possible before the coffee caps out and starts giving up muddy, harsh flavors.
If we have a high EXT coffee that tastes bad, we didn’t win. Having said that, here’s a big caveat for everyone making ready-to-drink coffee products: I personally think it’s fine to overextract coffee a little bit if you’re going to bottle it with milk and sugar. Some coffees pair better with milk when they’re overextracted. So there’s more flexibility when brewing in this case.
With that in mind, here are some other ways to increase extraction!
This is a big one: grind size. For most brew methods except espresso, grinding finer increases extraction. Breaking the coffee up into smaller pieces means you’re exposing more surface area to the brew water. If you’re dealing with espresso it’s very different because of the pressure, so in that case you’ll actually want to grind coarser to increase extraction (here’s the science behind that).
Another approach: try raising your brew water temperature. Water becomes a better solvent as it gets hotter. Even if eight barista trainers and a YouTube video said X temperature is TOO HOT, try it anyway. When it comes to coffee, always try everything anyway. Some coffees extract well and taste great when brewed with 212F water. Don’t hate me for my honesty.
You can also try extending brew time. More contact time between water and coffee means more extraction (up to a point). Another trick? Extend only the bloom time. The bloom is the first part of the pour, where the grounds are saturated with water then left to off-gas carbon dioxide for 30-45 seconds.
For some reason, this suggestion really makes coffee people lose their minds — but blooms do not have to be 30-45 seconds. You can bloom a coffee for 3 minutes. You can bloom it for 10 minutes. Nothing explodes. Increasing bloom time will almost always increase extraction, and it can taste really delicious too.
I know that’s a lot of variables! But I recommend you start by dialing in coffee-to-water ratio. Then adjust your grind to fine-tune. If ratio + grind isn’t enough to get you dialed in, then move on to water temperature and brew time/bloom time.
Note for coffee businesses struggling to dial in high EXT%:
Most specialty coffees can yield at least 18% EXT before they start tasting bad. If your coffee is capping out before you hit 18%, solubility could possibly be improved by adjusting roast profile (if that’s something you control). The topic of roasting for high extraction has less consensus, but most roasters agree that evenness is key. The more even the development, the more soluble the coffee. Evenness can be measured using an Agtron, Colortrack, or another color reader. Roasters typically take a color reading of the whole coffee bean, then take a reading of the coffee after it’s been ground. An evenly developed coffee has a smaller differential between those two readings.
So Now You Know About Extraction Yield
Although some coffee pros may want purchase refractometers for home use, I don’t see this as the most practical application — especially since the start-up cost is over $250. I’m not against home use, not at all! But I hope this piece has made it clear why the biggest benefits come from commercial applications.
And I hope it’s also clear now that extraction yield is pretty simple to understand, and definitely not worth gatekeeping. Especially when it can increase your profit y’all! If you’re a coffee pro and this article helped you, please consider sharing the knowledge with someone else, so they can share it with someone else. Nicely. Use the hot cocoa analogy. But be sure to tell them I actually make hot cocoa with oat milk.