Many of us think we have a grasp on making coffee. You know the drill: hot water, ground up beans, done. But the reality is that every single cup is a product of chemical extraction. It’s the process of drawing out soluble flavors from the coffee. This is something that needs to be controlled, because if it gets out of hand, you get a flat, unpleasant cup. Otherwise, you get a great, tasty cup. When you understand extraction, you stop seeing coffee as a black box and more as something you can control.
What is extraction?
Extraction is when water dissolves flavor from grounds. However, different flavors dissolve at different rates. Acids and bright flavors are usually extracted first, followed by sweetness and body. Last are the bitter compounds and dry aftertastes, which are not desired in your cup. The goal for every brew method, then, is to not extract as much coffee as possible, but to extract as much flavor as is desired.
Grind size
Grind size is arguably the most important factor. Finer grinds slow down the flow of water through the bed of coffee, which increases exposure time and allows for the water to extract more flavor. Coarser grinds, on the other hand, allow water to run faster, and thus extraction occurs over a more brief period. In the world of specialty coffee, it’s no secret that most issues start with grind size.
The difference between over-extracted and under-extracted coffee is often only a matter of how the coffee is ground. That’s why we need so many different grinders. If your brew is sour, it’s likely you need to increase exposure to water. If it’s bitter, then decrease the time water has with the beans. The same principle applies when using different brew methods. For example, French press is usually brewed with large coarse grinds since immersion brew is often a slow process; espresso requires the smallest fine grind in the barista world because the brew only takes 25 seconds.
Time
Time is often overlooked. Different brew methods require different amounts of time for their “perfect cup.” If your coffee brew is too weak, chances are it hasn’t been brewed long enough. But if you take too much time, you start pulling out unwanted flavors. For example, a french press or cupping session may take anywhere from 2 to 5 minutes, while a typical pour-over brew is done in three to four minutes. Espresso, on the other hand, should only take 25 seconds. Just as with the grind size, brewing time must be paired with a grind that’s best suited to the brew method.
Water temperature
Most of the brew methods used in cafes work best at around 90-96 degrees. Water acts as the solvent of extraction, and hot water extracts faster, so we need more hot water than room temperature water. If you get below that range, your coffee will seem underdeveloped and will have more of a sour taste, whereas if you go above, you’re more likely to get bitterness. Interestingly, the temperature at which you extract coffee doesn’t just determine the rate at which it will be extracted, it also determines the ease at which different components will be extracted. Minor changes in temperature, even as small as a few degrees, can slightly change the profile of flavors in your final cup of coffee.
The Impact of Water Quality
Since coffee is mostly water (at least the part that you drink is), what sort of water you use when making your cup is directly going to impact the flavor of your final result. Water that is too hard, or full of too many minerals will have a detrimental effect, leaving your cup muted and muddy, while water that is too soft can also leave your coffee tasteless and flat, making it an unpleasing drinking experience. For this reason, many sources recommend filtering your water when you brew, to ensure that the water used to make the coffee doesn’t add too much of its own flavor to the resulting brew, allowing the flavor profile of the coffee itself to fully express itself. This is one of the simplest things you can easily improve, without having to change any other part of your brewing.
Sweet, Sour, and Bitter
You will probably be aware that the flavor profile of any given cup of coffee can be described as sour, sweet, bitter, or some combination of all three. The balance between these flavor elements is what ultimately defines a cup of coffee, and you can think of your coffee as existing along the following spectrum:
- If your coffee is under-extracted it will be characterized as sour, sharp and thin.
- If you’re in the ideal zone, your coffee will taste as balanced, sweet, and round.
- Over-extraction will lead to a coffee that tastes dry, bitter and heavy.
It’s worth noting that at the most basic level, none of these descriptions are correct or incorrect in isolation. Rather, the goal is to be somewhere in the middle. This isn’t to say that you should aim for something that is exactly middle between sour and bitter and sweet; what is important, and what this balance ultimately depends on, is your specific choice of beans and the way you have chosen to brew it, among other things. Brewing coffee is very similar to tuning a sound system; it all comes down to ensuring everything sits together nicely in balance, and it requires some experimentation and adjustment to find a good spot to settle.
Why Your Coffee Doesn’t Taste The Same Every Time
Even if you stick to one particular recipe, your coffee will still taste different every time you make it. It’s not that anything has gone wrong, rather, it’s a natural consequence of a few factors beyond your control (to varying degrees). Coffee beans lose their freshness over time, so the longer a bag of coffee sits before use, the more it will differ from its original flavor profile. Grinds will change depending on the humidity in the room where they are being prepared for brewing, and water will change in mineral composition from batch to batch, all of which can lead to a coffee with a noticeably different taste compared to its previous iteration. Even something as small as a few seconds off your usual brew time can lead to slight flavor differences.
There’s nothing you can really do about most of these variations, and baristas wouldn’t even be aiming for a coffee that tastes the same every time, since it’s impossible to achieve this. Instead of aiming for exactitude of flavor, a professional barista would be aiming for some sense of familiarity, and will use their knowledge and experience with the way a system behaves to know when to adjust when something does shift.
From Recipe-Dependent to Recipe-Independant
Many sources will tell new brewers to follow certain recipes with an exacting degree of detail: use a specific quantity of ground coffee (or water), brew for a precise number of minutes or seconds, extract at a specified temperature range, and so on and so on. While this is a good way to start, it can quickly become a trap and lead to people becoming reliant on these rigid recipes. After learning to rely on these recipes, and how they lead to results, a coffee brewer will be able to start to understand the underlying process of extraction and how to achieve the results themselves. They will understand how a coffee that tastes sour should be fixed, or how a coffee that tastes bitter should be fixed, leading to better results and deeper knowledge of the craft.
Final Thoughts
Coffee brewing isn’t just a purely mechanical process. You will have more of the same outcome in your cup if you manage to keep all other brewing variables at an optimal and consistent state, but there is an inherent language of flavors to coffee brewing that goes beyond the realm of technicality, and it’s worth becoming familiar with. It is important to get a feel for how grind size, extraction time, temperature and other water quality factors all contribute to the overall result of your brewing in order to be able to make the best balance. The better you get a handle on this, the more brewing becomes something that is done on a whim, and not just a matter of following a recipe for the sake of it. And that, of course, is where the real craft of brewing coffee lies.