Coffee extraction refers to the process of using water to absorb the flavors from the coffee grinds. When the water runs through the coffee grounds, its mineral contents extract the flavors already present in the beans. At the end, those flavors should translate into the coffee you drink.
In this guide, we’ll discuss how you can step up your brew game by understanding how coffee extracts.
What gets extracted from coffee?
The following are water-soluble compounds that extract when brewing coffee:
| Compound | Associated Flavors |
|---|---|
| Caffeine | Bitter flavors |
| Acids | Sour flavors, usually of various fruits |
| Lipids | Viscosity / mouthfeel |
| Sugars | Sweetness |
| Carbohydrates | Viscosity, bitterness |
Out of these, we focus on extracting acidity, sweetness, and body as these are what make up the desirable flavors in a cup.
Why does extraction matter?
To make the most out of your coffee, you’d want to extract more of the flavors you like and less of the flavors you don’t.
Different coffees will naturally have different flavors inherent to them. The way a coffee is roasted will also impact how its flavors will pan out. Thus, requiring different levels of extraction per coffee to highlight certain flavors.
How you’ll extract more (or less) flavor will depend on variables like your brewing recipe, the type of water you’re using, etc.
How and when to measure extraction
Extraction is measured with this tool called a refractometer. It works by taking a small drop from your brew and then measuring the amount of total dissolved solids (TDS) in the coffee.
Based on the science surrounding coffee, a properly extracted brew has a TDS reading between 1.2 to 1.7. That’s usually an extraction yield of between 18% – 20%. Measuring extraction with these numbers can give some guidance that our brews fall in line with the generally accepted range.
But, at the end of the day, listen to your taste buds.
It’s not practical to constantly measure your brews with a refractometer. Unless you’re doing quality control at a café or you’re testing new brewing concepts, it doesn’t make sense to use a refractometer.
The Ideal Extraction
As a barista, I believe that a proper extraction presents itself most through flavor. The final cup should have a good:
- Acidity that isn’t overpowering
- Sweetness so there are no hollow flavors
- Texture so the coffee isn’t too heavy or too light
A proper extraction takes into account all these balances. You shouldn’t limit yourself to going outside of the TDS guidelines if it tastes good. Because, even if you can objectively measure extraction, the flavor experience is still subjective.
Example, your pour over brews might taste great with a TDS of 1.4. But when you switch over to an AeroPress, you might like it better with a TDS of 1.1. You don’t strictly have to increase your extraction just to hit a higher TDS. If the coffee tastes better at a 1.1 TDS, stick with that.
Read more about understanding coffee flavor notes here.
Over-extraction
The textbook definition of over-extracted coffee usually describes the following flavors:
- Bitter
- Dry
- Hollow and empty
I consider something to be over-extracted only when I taste too much of a particular flavor aspect. That could be too much bitter, dry, or heavy flavors. But those can also manifest in either astringent or muted flavors.
Under-extraction
The textbook definition of under-extracted coffee usually describes these flavors:
- Salty
- Sour
- Weak
To add to those, other signs of under-extraction are grassiness, wateriness, too bright of an acidity, a weak body, and a lack of sweetness. Among these, wateriness and unbalanced flavors are the bigger signs of under-extraction.
Weird extraction
We’ve talked about over and under-extraction. But there’s also weird extraction. There are some coffees that still taste unbalanced despite being properly extracted.
Meaning, you can have the right amounts of acidity, sweetness, and body. But they just don’t work well together.
In this case, you’ll have to extract less of one flavor aspect to let the other aspects really shine.
What causes over or under-extraction?
It’s common to hear that using the wrong grind size or water temperature are the main culprits. But I find that the bigger culprit is believing there is only one perfect extraction or one recipe for brewing.
It’s hard to have one catch-all recipe because not all coffees should be brewed the same way. That’s unfair to the different types of roasts, processing methods, and origins out there if you only brew one specific way for one specific kind of coffee.
Example, if you apply a recipe suited for old-school American roasts to a Nordic roast, you’ll under-extract it. Compared to the old-school American roast, Nordic roasts are more dense and need more effort to extract flavor. That’s why many tend to think all Nordic roasts are too tea-like and high in acidity – which isn’t true.
Your brew will depend on a lot of things. That’s why it is important to understand how coffee extracts. I personally adjust my brewing on the fly based on how quick the coffee drains, the crema I see at the top, etc.
It’s kind of like cooking. If you’re cooking a steak and you see that it’s cooking really fast. Will you strictly wait 2 minutes just to adhere to the recipe? No, you’d flip it already. Otherwise that side will overcook. Same thing with brewing – you have to observe how the coffee behaves and work with that.
How to extract coffee properly
Now that we know how each extraction can taste, let’s dive in to the actual process so we can make better brews.
Stages of extraction
We know by now that different flavors will extract at different times throughout the brew. This is easiest to test using pour overs. Essentially, you can isolate each flavor aspect by transferring your dripper into a different decanter with each pour.
If you want to try this experiment, you’ll need 4-5 decanters (depending on how many pours you do). But you’ll only need one dripper. After the first pour drains, transfer your brewing device to the next decanter and pour. Repeat until you’ve reached the desired amount for your brew.
| Time | Flavor Aspect |
|---|---|
| 0:00 – 0:30 / the bloom | Sharpest and unbalanced acidity |
| 0:30 – 1:00 | Calm to gentle acidities |
| 1:00 – 1:30 | Sweetness |
| 1:30 – 2:00 | Body, texture |
| 2:00 – 2:30 | Slight sweetness and more body |
To keep this example simple, we’ll use 30 second intervals to separate each flavor aspect. But the time which these aspects extract is not a hard rule. These depend on variables like batch size, ratio, dripper size, and grind size.
If you use a coarse grind, the rate at which these flavor aspects are extracted gets delayed because coarser grinds slow down extraction. If you use a fine grind setting, these flavors will be available much sooner. But you’ll extract bad flavors sooner as well.
These have to balance out with your dripper. If you’re using a fine grind with a slow dripper, your brew time will be irrelevant because bad flavors would have been extracted already because of the extended brew time.
Now that you know when certain flavor aspects are extracted, you can highlight any aspect you like by extracting more during those parts of the brew!
How roast date affects your brew
Always consider when your coffee was roasted. Flavors will usually peak within 2 to 3 weeks post-roast. When that happens, flavors are balanced and easy to extract. But before and after the coffee peaks, flavors are not balanced and you’ll have to find the sweet spot.
When coffee is fresh, it will taste smoky because the gasses from roasting have not yet settled. Conversely, as your coffee ages, its flavors will noticeably be less apparent compared to when it peaked. Over time, the acidity and sweetness of the coffee will fade while the body becomes heavier.
In either case, you’ll have to adjust the way you brew to bring out the flavors you want from the coffee.
Example, let’s say at peak your coffee had a nice and gentle acidity when brewed as a pour over. As it ages, you’ll have to work more to extract the acidity. Bear in mind though, that you won’t get as desirable a result if you extract the same amount as when the coffee peaked. Otherwise, you’ll risk over-extracting because there’s not as much to extract with aged coffee.
In this case, you can do a coarser grind to have more surface area. This will give more time to extract the coffee. Meanwhile, you can agitate early in the brew to focus the extraction during the acidity stage. Afterwards, you can do a gentle pour down the center to minimize the agitation in the later stages of the brew and prevent over-extraction.
This is one instance where shooting for a 20% extraction yield doesn’t make sense. It just won’t taste as good because the beans have already aged. Meaning, there isn’t as much to extract anymore.
What else effects your extraction?
The following brewing factors can either increase or decrease the amount of extraction in the brew. Except for grind size, increasing any one of these variables alone will also increase extraction.
Water composition
From a flavor perspective, lower temperatures help emphasize acidity while higher temperatures for sweetness and body.
You will also have to factor these with how hard or soft your water is. With higher TDS water, you can get away with lower temperature settings. Conversely if your water has a really low TDS, you’ll have to use temperatures closer to boiling.
Agitation
Agitation applies mainly to filter and immersion brews. While they seem to produce the same effect, certain forms of agitation can extract more than others. This is because they all disrupt the coffee bed in different ways – which also causes the coffee grounds to move around differently.
The movement of the different particles of coffee grounds also changes the total brew time, another factor in extraction
Ranked in terms of control over agitation (with 1 as the most control and 3 the least), we have:
- Stirring
- Pouring technique
- Swirling
Brew ratio
Coffee ratios refer to the amount of water you’re using per gram of coffee. Longer brew ratios extract more since more water is going through the coffee. Following this, shorter ratios will likewise extract less.
But from a flavor perspective, it’s the reverse.
Longer ratios have less intense flavor because they make the brew less concentrated compared to shorter ratios. They do, however, allow for more clarity and separation of flavors in the cup.
Brew time
This is a factor that’s also affected by any change in the other variables. Brew time will naturally increase when the other factors (except for grind size) are increased and vice versa.
Frequently Asked Questions
Should you always push for the highest extraction possible?
It really depends on the coffee you’re working with. Extraction theory is a guide to help with hitting the bullseye for flavor experience. But that bullseye changes depending on many factors.
Pushing for the highest possible extraction might make sense for certain coffees, at a certain point in time. But you might also notice that if you apply that to another coffee, it might not taste as good.
What’s the best extraction number / TDS?
Most scientific literature surrounding coffee would say it’s a TDS between 1.2 to 1.7. As a median, a 1.4 TDS should be a good place to be. But just like extraction theory, that should serve more as a guide than a hard number to chase. Go by flavors first instead of numbers.
Is it safer to slightly over-extract or slightly under-extract?
As a general rule, it’s hard to say. Certain flavors in a coffee only really come out when you don’t extract as much out of your coffee. While other flavors only really appear when you push for really high extractions. Either of which can be really nice if you know what you’re aiming for.
Remember that we shouldn’t think under and over-extraction as absolutes. Instead, we should think of them as ranges to guide us with how we taste.
About the Author
Tidow Gothong
Tidow is a barista and roaster that has worked in the coffee industry for 10 years. He runs 2 successful specialty coffee shops and a nano roastery.
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