This post will cover some basic extraction theory and the tastes associated with over, under and ideal coffee extractions.
Extraction is arguably the most important and least understood aspect of coffee brewing. It’s everything. Without extraction, you don’t even get a cup of coffee. Here’s my super simple and not 100% accurate definition:
Extraction is everything that the water takes from the coffee.
It’s pretty easy to sum up, but a lot more difficult to understand and apply.
For now, I don’t want to delve into fats and lipids and the micro-componentry of extraction. I want to communicate useful and relevant information, like how to taste extraction and how to manipulate it. Chemical analysis can come later.
When you mix coffee and water, a lot of things happen. The most relevant and easy to understand of all these things is that water dissolves a lot of coffee’s flavours. These dissolved flavours make up (almost) everything you taste when you drink a cup of coffee. The rest is undissolved stuff. This is mostly very very small coffee grinds that affect mouthfeel, but can’t be included in extraction because they’re just floating around in the water.
Roasted coffee beans are ~28% (by weight) water-soluble. This means that you can extract ~28% of the coffee bean’s mass in water. The rest is pretty much cellulose and plant stuff that forms the structure of the seed.
Water is pretty good at dissolving those soluble chemicals, but it needs help. If you throw a handful of coffee beans in hot water, you don’t extract much more than the outside layer. This is because the coffee bean’s structure is incredibly dense and complex; water can’t just pass through and collect all the flavour on its way. To help, we have to increase the surface area of the coffee beans; we need to ‘open them up’ so the water can easily get at all of the flavour. This is achieved rather handily by the use of a coffee grinder. It crushes the beans into a powder, exponentially increasing their surface area and allowing the water to do its work.
In an ideal world, we’d crush the coffee into an extremely fine powder, throw water at it and dissolve all of its delicious flavours. Unfortunately, this results in a terribly bitter and awful cup of coffee. Not all of the coffee’s flavours are good, so we have to control the amount of flavour that we extract in order to make a palatable cup.
We also can’t just use more coffee grinds and extract less of them to avoid those over-extracted flavours. Under-extraction tastes terrible as well (more on this in a moment).
Most people understand extraction as a two-way street. A street where we always try to steer the coffee towards the middle; avoiding both over and under-extraction.
For the next two Hustles, this simple analogy will be enough. Then once you’re all over it, I’ll be adding a layer of complexity that rounds everything out. Until then, we’re on two-way Extraction Street!
Under-extraction occurs when you haven’t taken enough flavour out of the coffee grinds. There’s still a lot left behind that could balance out the following undesirables.
Cast your mind to a shot of espresso that was far too short; a ristretto of a typical Specialty espresso roast. It’s sour, lacking sweetness, weirdly salty and has a disappointingly quick finish. These four things are the most obvious indicators of under-extraction. Let’s go through them in a little more detail.
This is a tricky one, especially with our desire for acidity in coffee. I hear lots of people ask “Aren’t sourness and acidity the same thing?” and it’s a very valid question; in a lot of languages ‘sourness’ is the same word as ‘acidity’. As you can imagine, this makes multilingual cuppings a little difficult.
To clear this up, I always define sourness as being negative. A sour flavour hits you quickly and aggressively. It creates an immediate physiological reaction, you might pucker your lips or it might feel electric or sharp on the sides of the tongue. Sourness is undesirable and distracting.
Whenever I talk about acidity it can be either good or bad. It’s more of a category of flavour than a positive or negative attribute. Example: “That coffee’s acidity is delightful” or “That coffee’s acidity is very sour” are both logical to me. Acidity is the umbrella under which lies all sour/juicy/bright/tart things. I could write volumes about acidity, but this week is all about extraction. Back to it.
In my opinion, the most important aspect to a coffee’s flavour is its sweetness. Sweetness is the best. Have you ever heard someone say ‘this espresso is too sweet!’? Think about that for a second. I strongly believe that we should always be chasing sweetness. It’s my holy grail: something that’s really difficult to find and stupendously rewarding once you get it. Under-extraction isn’t sweet. It’s far from it. It almost always displays an emptiness that leaves you with an unsatisfying ‘I-want-more’ feeling after drinking. The good thing about this lack of sweetness is that it also accentuates the sourness, making under-extraction much more obvious.
Not everyone agrees with me here, but I’ll argue til I’m red in the face that under-extracted coffee is salty. It’s not quite ‘sorry I added table salt’ salty, but under-extracted coffee almost always has the mouthfeel and/or taste of saltiness. From a tactile point of view, it’s kind of similar to the slipperiness you get from alkalinity (Don’t go and drink ammonia to learn this one. Just trust me).
#PocketScience – Acids and Salts are more soluble than Sugars. This is why an under-extracted coffee is sour and salty – the sugars haven’t had enough time or chances to dissolve completely just yet. 
A well extracted coffee has a finish that lingers for minutes (or hours if you’re lucky). This finish can feel as though someone has left dark brown sugar on your tongue, or as though you’ve just finished a toffee. Yum!
An under-extracted coffee doesn’t have this finish. Once you swallow, it disappears straight away. You’re not left with any pleasant lingering sensation. It’s an abrupt and unsatisfying end to your coffee experience. Less Yum.
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There are other flavours that indicate under-extraction, but these four are certainly the most obvious. Whenever you taste them, be sure that some part of your coffee is under-extracted!
Let’s now cast our attention to the opposite end of Extraction Street.
Over-extraction occurs when you take too much of the soluble flavours out of the coffee. This level of extraction results in unfavourable flavours.
Cast your mind now to an espresso of a typical specialty espresso roast that brewed for 40-50 seconds. Don’t pretend like you didn’t taste it when this happened once. It’s bitter, drying and hollow. These three things are the most obvious indicators of over-extraction. Let’s shine some light on them as well.
We’ve all been here. Coffee is bitter. Over-extracted coffee is really bitter. Unless I’m drinking Campari, I don’t want that much bitterness. A lot of this bitterness comes from caffeine, but there’s many other chemicals in coffee that contribute. A darker style roast that has achieved dry distillation will have many more of these bitter chemicals.
#PocketScience – There are thousands of chemicals (pretty much all poisonous) that trigger the exact same bitter signal from our taste buds. This is our body’s way of saying ‘don’t eat that’.
Dryness in coffee is so incredibly bad because it’s such a strong sensation, and it can last a long time. This sensation is called astringency and is the same as you get from unsweetened black tea, young red wine or white wines with extended barrel time. In wine, this effect is caused by polyphenols: chemicals that are readily found in plants, seeds, bark etc. These are arguably the same chemicals that cause dryness in coffee.
Polyphenols are bitter and bind to your saliva’s proteins. In layman’s terms, they de-lubricate your tongue, creating a sandpapery or dry sensation in the mouth (This shouldn’t be confused with the wine versions of ‘crisp’ and ‘dry’ – these are terms that denote bright acidity or low sweetness; not necessarily mouthfeel).
Hollow and Empty
This is a personal descriptor I like to use for over-extraction. The coffee just feels empty and lifeless, like you’ve extracted the living daylights out of it and killed everything in the process.
Well extracted coffee fills your mouth with richness. It’s luscious, smooth and, well, mouthfilling. Over-extracted coffee is empty, hollow, rough and just plain-old yucky. It’s this lack of flavour and character (rather than the presence of a particular flavour) that leads me to use the word ‘hollow’.
Those are the key over-extracted flavours. Of course there are more, but these are super simple to identify, and should have you identifying over-extraction in no time!
The most important thing to note about all of these flavours is that they are generic. You can get them from the most expensive Gesha in the world, and you can get them from sub-commodity grade rubbish. These flavours aren’t desirable. Most of us here are in Specialty Coffee, which means we’re trying to create a product special enough for the customer to want to pay more for it. Extraction-related faults are anything but special.
Now for the sweet spot, the yum-zone, the goods.
Ideally Extracted Coffee
A well extracted coffee is a little miracle. A lot of work has gone into balancing countless variables to produce a tiny cup of deliciousness, and it’s imperative to know what this tastes like.
Cast your mind to the best damn cup of coffee you’ve ever had. It’s sweet and ripe! There’s a clarity to the flavour, like it’s transparent. The acidity is balanced and positive, perhaps complex if you’re lucky. And the finish goes for ever. This is the jam, and you want to know more about it.
Sweet and Ripe
As I said, the Holy Grail. I’ve spent countless hours teasing more ripeness out of coffees. It never gets old.
Think of a plum or similar stone-fruit as it ripens. At first there’s a lot of acidity and tartness, then it gradually gets sweeter. The sugars are developing and becoming richer, heavier, more cloying. Then it hits a point where just holding the fruit near your nose enables you to smell the sweetness. Right there. That’s the sweetness and ripeness you want from coffee. If you’ve never had that, you’re in for a treat one day soon!
Clarity and Transparency
George Howell has a way with words. He describes the processing method of coffee as being ‘the window through which you see the coffee’. I like to extend this analogy by thinking of the extraction (and roasting) as another pane in that window. If you have over or under-extraction muddying up your glass, it’s harder for you to ‘see’ what the coffee really tastes like. Generic extraction faults are distracting and can impair the provenance of the coffee you’re serving.
Fine, complex and definable acidity is truly something to behold in coffee. Acidity is something that’s incredibly beguiling, but also frustratingly flighty. When you get acidity that reminds you of a specific fruit, or even a wine, you’re in the green. If that acidity is so definable and intense that you can pinpoint a variety of fruit and remember the last time you ate it, you’re nailing it.
Finish for Days
This is self explanatory. A good finish goes nearly forever. A sure sign of good extraction.
So thats the good, the bad, and the ugly of extraction and flavour. Hopefully now you will notice a few of these flavours in your day to day coffee tasting, and be able to link them with the appropriate level of extraction.
Next week, I’ll be covering the two main factors involved in changing extraction!
What flavours do you associate with ideal, under, or over-extracted coffee? Have you found a good way of communicating those flavours to others? Let me know in the comments!
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