BKG Brew Guide: Coffee Extraction 101
Have you ever tasted a phenomenal coffee at a cafe, got the same coffee from the coffee roasters, but then no matter how many times you tried to recreate that divine moment, it just didn’t quite taste the same? Have you ever wondered why?
disclaimer: squeezing coffee beans is NOT a brewing method, do not attempt this at home.
Today, we are jumping on a big and ever evolving topic: coffee extraction. Although roasted coffee is generally regarded as a shelf stable product, but like food and wine, even with top quality products, how you prepare, even to how you consume coffee can result in very different experiences. We will talk about the basic parameters that affect the quality of your brew. All is applicable to a home brewing setup. I will talk about what the relation is between those factors and how to utilize tools and the environment you have at home to maximize an ideal extraction.
WHAT IS COFFEE
Luscious coffee trees produce lots of white tiny blossoms that look like scattered starlight caught by the branches. It is said that the flowers have a strong scent that reminds people of jasmine. Coffee blossoms then bear coffee cherries which can take up to about 9 months to fully ripen. Environmental factors, genetic factors and agricultural practices will all impact the quality of coffee.
Coffee is a labor intensive crop to harvest. Because it’s very common for a single tree, even a single branch to show different stages of fruit bearing, only by handpicking can you make sure only the ripe ones are picked. After the harvest, cherries need to be processed. After the pulp is removed, the seeds exposed and dried, the green coffee travels, oftentimes across the world, to your local roasters. Green coffee at this stage shows very little trait to the beverage that we enjoy so much. Only by roasting meticulously can one unlock the explosion of flavors, it is then the coffee beans that we know, small but mighty, come a long way.
WHAT ARE WE EXTRACTING?
A lot of dramatic chemical reactions happen when you roast green coffee. As a result, you’ll find amino acids, sugar, carbohydrates, proteins, organic acids, minerals, lipids, caffeine and trigonelline in a roasted coffee bean. In fact, more than eight hundred chemicals have been identified in coffee beans. The intricate symphony of these chemicals is what eventually brings us the flavors, aromas and health benefits of coffee.
Water is an effective medium to draw those chemicals out of the roasted coffee. When coffee is “under-extracted,” it means too little of the flavor was removed. The resulting coffee can taste weak, sour, and salty; “over-extracted” means too much solids were removed from the beans, including bad-tasting chemical compounds, resulting in a strong, bitter and astringent cup.
The ideal extraction is subjective, but it’s generally regarded that 18% to 22% is a good range. A properly extracted cup of coffee will taste smooth, balanced and naturally sweet. There will be a nice clarity in the flavors and a pleasant lingering finish.
Extraction can be manipulated by roast level, brew time, water quality, temperature, brew method and grind size. All those factors connect with one another. The process of finding the best combination is very similar to adjusting the colors of a photo: when the image looks too blue, you want to increase red levels, so the final shot can be balanced, vibrant and attractive. That is also what we are looking for in a cup.
Once we understand what those factors are, how they affect extraction, we will discuss how we can apply those “”dials” to assist us in finding a better extraction.
Cinnamon, full city, french or italian? Those once exotic terms are what people used to describe roast level. From light to dark, you will notice the terms are consistent with the appearance of the roasted coffee beans, which also correlate to how long the beans have been roasted.
Lighter looking beans spend less time in the roaster. You might also hear people calling lightly roasted coffee Scandinavian style which is because this is a popular roasting style among Scandinavian specialty coffee roasters. You usually find a lot of bright fruit notes, higher acidity, floral with lighter roasted coffee; on the other hand, some might find a light roast lacking body, tasting tea-like, sometimes with hints of tomato, peanuts and vegetal notes. While light roasts can give us a lot of subtlety and a delicate profile, it is at the same time harder to achieve higher extraction. Sometimes, when the coffee is roasted too lightly, it might not have enough Maillard reaction to produce enough sweetness and balance.
Darker roasts are better at achieving extraction. The taste profile is usually more nutty with plenty of chocolate notes, hints of caramel. The downside is that it loses more tender fruit notes, and some intricate single estate flavors might not be as pronounced when the coffee is roasted darker. In extreme cases, darker coffee may suffer a higher oxidation rate and taste stale, dull and even medicinal.
Steeping tea is a perfect example explaining brew time for coffee. The less the contact time, the lower the extraction; the longer it takes to finish the brew, the higher the extraction. On a side note, the caffeine content is most directly affected by brew time. That’s why cold brew can sometimes feel like a power shot.
Coffee is up to 98% water. Very much like your cocktail mixers, if your water quality is questionable, it’s hard to get coffee to taste good. And in some cases, water actually directly enhances/dissuades a good coffee extraction.
A quick guideline to water chemistry for coffee is pH level and water hardness. A good range for pH level is between 6.5 and 7.5. The lower the number, the more acidic the water is and more effective it is at extraction; a water hardness between 50 ppm and 230 ppm is considered acceptable. The lower the number, the softer the water is, and the easier it is to extract solids from coffee.
A very important side note about water quality is that it can manipulate extraction to enhance particular taste notes and how our palate perceive taste. For example, with a different mineral content, a coffee that tastes like stone fruit might exhibit more citrus notes with a different water. Water is a very powerful tool to fine-tune a very defined taste profile. We will cover the topic of making your own water for coffee at home in the near future.
The hotter the water, the more thermal energy it has, therefore the better it is at dissolving solids out of coffee. People sometimes fear a hotter temperature might “burn” their coffee. This may be a confusing term as boiling water cannot burn coffee. However, because hot water is so effective at extracting coffee, it brings more bitter chemicals that’s already in the roasted beans.
All roads lead to Rome, there are so many brewing methods nowadays we can’t even count. While the end result can be quite similar, not all methods work the same. When talking about extraction, we especially want to look at how a method agitates and penetrates coffee. No one method is indefinitely better than the other, the more agitation and penetration one provides, the better extraction one gets.
Brewing method can be categorized as following:
. decoction (through boiling, like cowboy coffee, turkish coffee)
. immersion (through steeping, like french press)
. percolation (when water pass through coffee gradually, like gravitational pour over, or a pressured percolator)
. pressurized method (as with espresso).
Even with the same brew method, operation can also affect the extraction. Take pour over for example, when you pour water more forcibly, it creates more agitation. whereas slowly dripping your water through coffee will end with a lower extraction.
Grind size directly decides how easily coffee will be extracted. With a coarser grind, it has less contact surface, so the extraction won’t be as easy as finer grounds. This is a simplified guideline. The complicated caveat here is the composition of your grind particles.
It is physically impossible to demand a perfectly uniform grind from any grinder. If we observe our coffee ground with a magnifying glass, we will notice there are some extreme fines and a few pieces of boulders, no matter what. The real difference is the range of those particles and the composition of the batch. One example for consideration is when your grinder produces very bipolar distributions, the coarser grounds don't get extracted enough but the micro fines are over-extracted, The finished brew can’t be balanced because you can’t extract evenly.
These factors may not pose direct influences on coffee extraction, but they can help improve the result or provide a temporary solution.
Roasting generates a lot of gas. Some of the gas gets trapped inside the beans in a compressed environment. Through the course of up to 2 weeks, the gas gets gradually released back to the ambient environment. If those coffee beans are used before the degas subsides, the center of the beans will have different consistency compared to the edge of the beans. Also some lipid and other more motion-fluid compounds are pushed to the outer layer of the coffee beans during this degassing period. So before the lipid gets the chance to redistribute itself, different parts of the coffee beans will have quintessentially very different chemical make-up.
So while this might not have a direct effect on extraction, it can result in an even/uneven brew.
When you have a higher coffee to water ratio, your coffee will taste stronger; on the other hand, some diner coffee may taste watery when they don’t put enough coffee in the brewer. However, when this is a quick fix sometimes, it doesn’t necessarily mean that you’d get a higher extraction rate with more coffee.
Your palate is the most useful tool when it comes to dialing in coffee. If you are not happy about a brew, think about what you don’t like about it and how you can improve it. Now that we’ve talked about what factors go into achieving extraction, utilize this information as if you have physical dials which you can tone up/down the brew. It’s always recommended to make small changes so you can make sure you’re not over-correcting yourself. Try to make the changes simple, too, so that it would be clear what adjustments are effective.
We will take a look at a couple of short examples below. But foremost, remember we are looking for the sweet spot where ranges of extraction rate from different factors come into a perfect harmony.
EXAMPLE 1: watery and slightly too sour
This is likely an under-extracted result. So we need to look at the factors we can use to boost the extractions. A finer grind size? Maybe introduce more agitation when brewing? Perhaps a hotter brewing temperature? If you use a french press, maybe leave the coffee in for an extra two minutes?
EXAMPLE 2: intense and too strong
This can be either over-extraction or higher brew strength. So we need to first determine which it is before we decide how to fix it. Drop a little bit of water in the coffee, does that make it better? If it does, that means the coffee is more concentrated than it should be, so next time use a less coffee to water ratio. If the coffee tastes more watery but still has the bitterness to it, that’s a good indicator that the coffee itself is over-extracted. So, we need to figure out a way to bring the extraction down.
Can you coarsen the grind size? Do you have a coffee sifter to remove the extreme fines from the coffee ground? Is the water distilled? If so the pH might be too acidic and the water too soft. If you are using an AeroPress, maybe try starting to plunge earlier?
EXAMPLE 3: I like the taste over all, just wish it was sweeter
This is a tricky scenario. Higher extraction usually gets more sweetness. However, remember we were talking about how dialing in can feel like adjusting colors sometimes? This is especially true when you’re dialing in on a very minute perspective. We need to think about how we can boost extraction without going overboard.
Can you increase brew time? hotter water? finer grind? What if after you just make the grind size finer, it starts to taste bitter? maybe (counter-intuitively) use colder water to compensate?
The topic of coffee extraction is our everlasting effort to find consistency and the ability to recreate a great coffee so that we can share it with more people. It’s definitely one of those subjects that after hearing the answers, you find yourself having more questions. Here at BKG, it’s our daily routine to ensure quality. All of our brewing guides won’t be possible without those dialing in steps. We really hope you find this blog useful. We hope we cover some issues that you’ve encountered.
If you’re inspired by the challenges of dialing in, make sure you subscribe to our BKG 3 packs so you will never run out of coffee, and you will always have variety. It’s also automatically discounted. We got you!
Let us know what you think! Do you agree with us? Are you having any issues brewing a cup that you’re happy with? We would love to hear from you!