Have you ever tried the same coffee in a French press or a Chemex? All the ingredients are the same, right? So why does your final cup of coffee taste different?
The answer lies in the complex world of coffee extraction. In other words, how much of the coffee flavor is extracted from your beans and ends up in your drink.
So how does it work? And what do you need to know to get the best out of your beans and into your cup?
We’re here to help! We’ll take you through everything you need to know to discuss extraction like an expert. And more importantly, when you’re done you’ll have all the information you need to make a perfect cup of coffee.
Coffee Extraction: Knowing the language
There’s a lot of complicated terminologies bandied around when it comes to discussing coffee extraction. Don’t let it put you off! We’ll take you through each of the terms you’ll hear and explain how they fit into the extraction process.
An easy one, this. It just means the amount of coffee you use to make a single serving.
When you add water to your coffee, some of the beans will dissolve. The extraction yield is simply how much of that dissolved coffee bean ends up in your drink. It’s sometimes referred to as “solubles yield” or just the “yield”.
You will often see it expressed as a percentage of the original mass of the coffee grounds. So if you had an extraction yield of 20%, it would mean that 20% of your original coffee grounds ended up dissolved in your drink.
Strength and TDS
Everyone knows what’s meant by a strong coffee, right? Well, not always. Is a coffee with strong floral notes as “strong” as one with strong chocolate notes?
To get rid of this kind of problem, “strength” has a very specific meaning when it comes to coffee extraction. It means the percentage of total dissolved solids – those dissolved particles of coffee – in the final drink.
TDS is expressed in parts per million and is measured with a device called a refractometer. It works by passing light through the liquid and measuring the change in the angle of the light wave.
You might think that a greater extraction yield means stronger coffee, but that’s not the case.
Although a high yield means more TDS in your drink, it doesn’t mean that the proportion of TDS is high. That depends on how much water you’ve added to the coffee.
So if you’ve dissolved a lot of the coffee but used a large amount of water to do it, your proportion of TDS will still be low. In other words, your coffee can be well-extracted but still weak.
The final part of the equation is the brew ratio. This sets out how much water you’ve used to make how much coffee. So if you’re drinking an espresso with a brew ratio of 1:2, it means that your final drinks weigh twice as much as the coffee grounds you’ve used to make it.
To give an example, if you’ve used 18g of coffee grounds to produce 36g of espresso, your brew ratio is 1:2. Some people prefer to express this as a percentage of dose to yield. In this example, the dose is half of the yield, giving you a brew ratio of 50%.
What does extraction mean for taste?
To understand this, we need to look at the chemistry of what happens when water and coffee mix.
About 28% of a roasted coffee bean is made up of material that can dissolve in water. The rest is substances like cellulose that make up the structure of the plant.
Of course, all those materials are inside the bean as well as on its surface. So to get at them, the beans have to be ground before hot water is added.
So far so good. We want to get as much flavor as possible from those beans, so we grind them as finely as possible and then steep them in hot water, right?
Not quite. Because although the bean contains lots of delicious flavors that you want to make it into your drink, there are also some that you want to avoid. And different flavors are released at different stages of extraction.
There are some easy ways to tell the difference between under- and over-extracted coffee, and it’s all in the taste.
Under-extracted brews will be sour, or even salty. This is because the acidic flavors that are extracted first need to be balanced with the sweetness that occurs later in the extraction process. If that hasn’t happened, the fruity tastes that could have been delicious will instead taste sour.
Fortunately, under-extracted coffees will have a quick finish – in other words, the flavor won’t linger in your mouth.
Over-extracted, coffee, on the other hand, will taste bitter. Think of the taste of really dark chocolate.
Again, these flavors can be delicious if balanced with the acidity released earlier in the extraction process. If the coffee has been over-extracted, however, the bitter flavors will overwhelm all the rest.
What you’re looking for is a well-balanced extraction that gets the best of both worlds.
There’s a simple relationship between the extraction yield and the flavors that you’re looking for. And although the flavor is a subjective thing, this is one instance where there’s an objective measurement to help out.
Back in the 1950s, the Coffee Brewing Institute calculated that a yield of between 18 and 22% gave the best results.
What this means is that if less than 18% of the original coffee grounds end up dissolved in your drink, you’ll be tasting under-extracted, sour coffee. If it’s more than 22%, you’ll get the bitterness of over-extraction.
So if your coffee doesn’t taste the way you want it to, how do you go about changing the yield? There are four things you need to bear in mind: water temperature, time, grind size and brewing method.
Let’s look at each of them in turn.
The temperature of the water you use to make your coffee has a big impact on extraction. Simply put, the hotter the water, the quicker extraction takes place.
If you enjoy making cold brew coffee, you’ll know that you need to set aside a long time. The cold water used means that it takes at least 12 hours for your drink to be ready. Some recommend a minimum of 18 hours.
Even with this length of time, however, cold water won’t release all the particles that would dissolve at higher temperatures. That will mean the resulting coffee has a “flatter” taste than iced coffee, which is made with hot water then chilled.
The hotter the water gets, the faster the brewing process happens. That means that at the other extreme, if you boil coffee you’ll find that flavors and aromas disappear in the steam. And because brewing happens so quickly, your margin of error to avoid unwanted flavors becomes very narrow.
The resulting cup of coffee can taste both weak and overwhelmingly bitter.
So how do you get the right balance?
Keeping all the other factors the same, the ideal brewing temperature is usually considered to be between 195 and 205 degrees Fahrenheit. This can vary, however, according to your brewing method.
For cold brew, the variation is obvious, but it’s even the case for some hot coffees. Experts in using the AeroPress have found slightly lower temperatures work better. The winners of the World AeroPress Championships consistently brew at between 165 and 185 degrees Fahrenheit.
We’ve already seen that hot water increases the rate of extraction. That means that time also plays a part in how well your coffee is extracted.
Trying to make a cold brew coffee in minutes will leave you with a drink that’s barely more than water. Leave it only a few hours and the under-extracted coffee will have that unpleasant sour flavor we want to avoid.
Use a mixture of hot water and steam, and you’ll want to measure your extraction time very precisely. We’re talking seconds, not minutes, to get the perfect result from an espresso machine.
In short, if you don’t leave enough time for brewing, you’ll miss out on all the good flavors of the coffee. As a result, the final cup won’t be balanced.
If you leave too much time, though, you’ll end up dissolving compounds you don’t want. The result will be that undesirable flavors enter your coffee too.
The right time is a product of the other factors. Temperature, grind size and brewing method all have implications for the right amount of brewing time. Even the recipe can make a difference: if it calls for stirring the grounds, it’s likely to require less time.
So decide on your brewing time after you’ve chosen your brewing method. We’ll come to that last of all.
As we’ve seen, the point of adding water to coffee is to extract its flavors, most of which are inside the bean. The more finely ground the beans, the more surface area there is for the water to come into contact with.
So if you keep everything else the same, more flavors will be extracted from fine than coarse ground beans.
That doesn’t mean, though, that fine grinding is always the way to go. Too fine a grind combined with the wrong brewing method and you can be left with over-extracted coffee.
Even worse is the combination of a fine grind and a filter that’s designed for coarse ground coffee. Put a fine grind in a French press, for example, and you’ll end up with a mouthful of coffee grounds!
If you have a burr grinder, it’s easy to test the difference for yourself. Grind two doses of coffee, one fine and the other coarse. Then brew them the same way and for the same amount of time and taste the difference.
And if you’ve used good coffee beans but find the flavor insipid, the chances are they’ve been ground too coarse. Too bitter, on the other hand, and a fine grind may be too blame.
Brewing methods and brewing ratios
In practical terms, picking a brewing method is the easiest place to start on your quest for the ideal extraction. Any coffee recipe will be based on a brewing style, and will give a specific coffee to water ratio. Grind size, water temperature and brewing time can then all be tailored to give the best results.
These examples show how all the different factors work together to determine extraction yields.
In this case, the water temperature will drop while the coffee is soaking. For that reason, there is a higher coffee-to-water ratio than with other methods.
Because the coffee will be sitting in the water, a medium grind will avoid over-extraction (and grounds in your coffee!). You can, though, use a slightly finer grind with a shorter extraction time and still get good results.
Drip filter coffee
Here, the water temperature is higher, so use a lower coffee-to-water ratio. Watch out for too fine a grind, as it can clog up the filter.
Today’s espresso machines allow you to change the amount of water you use. A good machine will also maintain the water at a near-constant temperature.
A fine grind allows the water to extract as much flavor as possible as it’s pushed through the coffee. And controlling the time will avoid over- or under-extraction.
So there you have it: you understand the language of extraction. And you know that the perfect yield is all about getting the right balance. Combine water temperature, time, grind size and brewing ratio in the right way, and you’ll reach coffee perfection!
If you have questions, please comment and let us know.
And now you know the theory, why not try out the practice? Experiment by changing some variables, and experience the tastes of different extraction levels for yourself.