by Darren Oliver
It has happened to each of us: you open a packet of freshly roasted, aromatic beans, brew them in your favorite brewer, pour it into a cup, take the first sip, and… something is wrong. Instead of rich, intense aromas, you feel only bitterness, an unpleasant aftertaste, and even dryness in your mouth.
What happened? Well, probably your coffee was over extracted. However, don’t worry! In this article, we’ll explain the science behind over extraction, its symptoms, and solutions to help you brew the perfect, flavor-balanced coffee.
The Science of Coffee Extraction
To understand exactly why a phenomenon like over extraction occurs at all, you need to understand the science behind coffee brewing itself. Coffee (as a beverage) is the result of a simple combination of ground coffee beans and water. Of course, a whole range of different chemical processes take place during the process, and we will devote today’s article to just one of them. The water dissolves the coffee particles, and this solution forms what we then call coffee. However, not all the particles are dissolved, as you can observe with the naked eye: grounds remain in your coffee brewing device.
In addition, the coffee particles will not dissolve on their own: see what happens when you drop a tablespoon of ground and unground beans into a mug of hot water. With the naked eye, you can see that it changes color much faster if you use ground beans: more surface area equals more solubility.
Coffee also dissolves faster in warm water – so when macerating coffee for cold brew, leave it in cold water for 12 hours (or more!). If it took less time, not enough coffee molecules would dissolve in the water, giving us under extracted coffee (but about that in another article maybe). The warmer the water, the faster the extraction!
How else can we help the extraction? For example, by stirring the coffee particles (on the same principle, sugar in coffee dissolves faster if we stir it with a spoon). If we pour a strong stream over the ground beans during brewing, we will agitate them, making the extraction level higher. The same can be achieved by stirring the coffee with a spoon during brewing.
However, as in everything in life, a certain balance must also be maintained in coffee brewing. This is because we cannot extract coffee indefinitely. This is when over-extraction – the main subject of our article – occurs.
How Do You Recognize Over Extraction?
Now you may be wondering, how are you supposed to know if your coffee has over extracted? Well, the matter is quite simple: over-extraction is a relative thing, so it’s up to you alone to determine whether what you smell in your cup is over-extraction – some people prefer coffees with lower and some with higher extraction. However, there is a certain set of characteristics that are defined by this very term.
Your coffee is too bitter. Of course, a slight bitterness isn’t necessarily a bad thing – bitterness is present in grapefruit and dry wines, for example, and yet we appreciate the taste. However, we are talking about a bitterness that overshadows all the rest of our brew, that does not allow us to feel other flavors, does not compliment them, but rather kills them. Since bitterness has its origin in the chemical compounds that are dissolved last in the brewing process, you have likely led to over-extraction.
Dry mouth. Sometimes coffee can be delicious, juicy and leave a wonderful feeling in the mouth. In the case of over-extraction, however, it’s a bit different: your mouth becomes dry, as happens when you drink dry wine or strong black tea. This phenomenon is called astringency, drinking coffee that has been over extracted, you can feel it in your throat, but primarily at the surface of your tongue. It happens, because certain compounds in over extracted coffee bind with proteins in your saliva, making your mouth less lubricated.
Your coffee just tastes empty. We partially mentioned this earlier in the text. Good quality coffee will always be complex, rich, and flavorful when brewed properly. However, an imbalance of flavor violently affects the complexity of a given brew. This is what happens when there is over-extraction and dominant bitterness occurs.
What Can You Do About Over Extracted Coffee?
You already know how to recognize that over-extraction has occurred in your coffee. Being equipped with this knowledge, you can fight this messy phenomenon! So let us give you some ways to fight over-extraction that will make your coffee delicious and aromatic.
Grind your coffee a little coarser. This will reduce the surface area of the coffee particles a bit, so extraction will happen a bit slower. However, be careful not to overdo it: this is because then you may experience under-extraction.
Use water at a lower temperature. In the earlier part of the text we already touched on the effect of temperature on extraction. Remember, however, that the changes should be minimal. If over-extraction occurs at 98 degrees Celsius, try conducting another at 95 degrees Celsius.
Pour the coffee in a gentle stream, without stirring. It may be that you agitate your coffee too much. Try being more gentle, and not stirring the coffee (or stirring less).
Try using “softer” water. Believe it or not, the water that you use to brew your coffee affects extraction immensely. That’s why professional baristas often “custom” their water by adding minerals to demineralized water. If over extraction occurs, try using softer water, the ideal should be between 120-200 ppm (this information is always written on the bottle).
Summary
This article will help you brew coffee even better in the future. You already understand what over-extraction is, know what can affect it, as well as how to counteract it. There’s nothing left for you to do but enjoy a cup of delicious, complex, and, above all, balanced coffee!