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What Is Coffee Extraction and Why Is It Important?
The first thing we need to cover is what extraction means. We could go into a lot of depth right now and look at the complex chemical interactions that define coffee extraction but the bottom line is, it’s simply the dissolution of the soluble coffee components into water to give the water that rich color, strong flavor, and beautiful aroma.
Extraction is the dissolution of the soluble coffee components into water to give the water that rich color, strong flavor, and beautiful aroma.
To understand a bit more about extraction we should start with the coffee bean itself. The coffee bean isn’t actually a bean but is instead the seed of the coffee plant. This seed is a little package that contains everything a new coffee plant needs to establish itself in the earth and grow into a strong and healthy plant. This means they contain complex carbohydrates, acids, and fats. These components are the key to delicious tasting coffee, but the beans need a little help to release these tasty elements into your morning cup of coffee.
The beans need to be exposed to heat to break down the carbohydrates into simple sugars, reduce the acidity and release some of the oils so these tasty elements can more easily dissolve in hot water. This transformation happens during the coffee roasting stage and turns the beans from a cool green color to the darker brown beans you’ll see at coffee shops.
The extraction process is very important when it comes to brewing coffee as without it, the water would have no flavor of the coffee at all. When extraction is out of balance, you end up with coffee that’s described as over-extracted (tastes intensely bitter and leave your mouth dry) or under-extracted (tastes sour). A well-extracted cup of coffee tastes sweet and rich with complex flavors. It has a full-bodied mouthfeel and a brightness that comes from the remaining acids.
Understanding extraction is really important when brewing coffee and if you get your extraction skills perfected, you’ll be known as the expert coffee brewer amongst family and friends.
What Impacts Coffee Extraction?
Probably the most significant thing that affects your coffee extraction is the grind size you choose. A coarse grind consists of larger coffee particles so overall the coffee has a smaller surface area in contact with the water. This means the coffee needs to be brewed for longer to extract a good flavor otherwise it can end up weak and under-extracted.
A finely ground coffee has a larger surface area so the flavors are extracted quicker compared to coarse coffee. This means the coffee can easily become over-extracted.
The most important point with grind size is to select a grind size that suits your chosen brew method and use a good quality, burr grinder. These ensure an even particle size when grinding the coffee beans so gives a well-balanced, more consistent flavor.
The ratio of coffee to water is a really simple factor to consider but makes a huge difference when it comes to flavor extraction. If you don’t add enough coffee then you will struggle to get a rich flavor. For pour-over, drip coffee, and French Press a good starting point is a 1:15 coffee to water ratio. For every 15 grams of water add 1 gram of coffee. This value isn’t set in stone and you can always tweak and adjust it until the flavor suits you best.
For brew methods like espresso, this ratio is very different at around 1:2.
The time that the coffee stays submerged in water has to be just right to ensure you get a good extraction but avoid the bitterness. The general rule is, the finer the coffee is ground, the shorter the extraction time needed. For very finely ground espresso, the extraction time is 25-30 seconds. For French Press with its coarse grind, you need to leave the coffee to sit for four minutes.
The bed depth when brewing coffee describes the height of the coffee grounds as they sit ready to contact the water. If the bed depth is too shallow then water can end up channeling through small areas giving an under-extracted, sour cup of joe. If the bed depth is too deep then the water contact time is too long leading to bitterness.
To avoid an unsuitable bed depth, make sure you follow the manufacturer’s instructions for your chosen brew method and use a coffee maker that can handle the brew size you need.
The hotter the water used for brewing coffee, the more the particles move around and make themselves available for the coffee flavors to dissolve into. If the water is too cold then the coffee will end up tasting weak and thin. The ideal water temperature to brew coffee is between 195-210°F (91-99°C) for optimal coffee extraction (generally on the lower end of this range for darker roasted coffees and the higher end of this range for lighter roasted coffees).
It’s worth mentioning that there is one way to get around the water temperature issue. You can brew coffee in cold water (called cold brew coffee), but it needs to sit and steep for 12-24 hours to brew correctly. The longer extraction times helps get around the cold water issue.
The quality of water used to brew coffee can influence the extraction. Impurities in the water, which affect the pH, the acidity of the water, and the hardness of the water can all impact extraction. The idea of how different elements in the water can impact extraction is beyond the scope of this article (here’s a great article if you are interested in learning more), but to keep things simple, the best thing to do is use filtered water as this results in a great tasting cup of coffee that has been perfectly extracted.
The basic function of coffee extraction comes from diffusion. As the water contacts the coffee grounds the flavor molecules gradually move from an area of high concentration where the coffee sits, to spread out into the water. Diffusion is how water naturally reaches equilibrium, but it is a slow process.
This is where agitation comes into play. If you agitate (move around, stir, shake) the coffee, this increases the water to coffee contact and speeds up diffusion. If you don’t stir the coffee after you add the water then pockets of air can remain trapped in the coffee so this also acts to create an uneven extraction.
Brew methods like Aeropress come with their own stirring wand to allow you to agitate the coffee and French Press is another good example of a brew method that needs a good stir.
Different brew methods will affect the extraction of your java due to all the issues described above. Here are some of the main issues with each brew method and how to avoid them.
Pour over coffee controls the flow of water by the design of the set-up so you don’t need to worry about brew time. The main issues people face with this brew method is water temperature (too hot or too cold), grind size, or using an appropriate amount of coffee for the size of the brewer. Make sure you buy one that suits the number of cups you need and don’t try to overstretch the capacity.
Like the pour-over, the main issues that arise with the French Press is the grind size and the water temperature. Make sure you use a very coarse grind and water that is 195-205°F (91-96°C). Submerge the coffee, give it a stir and leave it to sit for 4 minutes before pressing the plunger.
Brewing espresso has more of an art to it compared to most brew methods. You need to get the grind size just right to ensure a good extraction and make sure the coffee is loaded and tamped corrected when added to the portafilter. The shot is pulled over 25-30 seconds and you’ll know it’s a good one if there’s a thick layer of crema on top. Espresso brewing varies with different machines used as well as different types of coffee so it’s really something you need to practice to get it perfect. (If you’re interested in improving your espresso at home, check out our article with some tips!)
The golden rule with cold brew is to use coffee that’s very coarsely ground. Cold brew can be brewed much more concentrated compared to other coffee brew methods so you can use a ratio of 1:7 to make cold brew concentrate (this can be diluted later on) or something that is more drinkable without dilution at a 1:12 or 1:15 ratio. Leave the coffee to brew in cold water for at least 8 hours but it can be left for 18-24 hours before it starts to become over-extracted.
Over vs Under-Extraction
So you’ve just finished brewing your morning cup of coffee and it tastes… a bit off! Here’s a general guide to over vs under-extracted coffee, how to spot it, and what to do with it.
If the coffee tastes bitter, hollow, dry, and just lacking in depth of flavor then you have an over-extracted brew. The most likely culprit is you’ve left the coffee stewing for too long, you’ve used coffee that’s too finely ground, or used water that is too hot. At this stage, most of the sugars that give the coffee that rich, sweet flavor have broken down so you’re left with a cup that has no sweet elements to it.
The best thing to do with an over-extracted cup of coffee (aside from throwing it away!) is to add milk, sugar or another kind of sweetener to balance out the bitterness. A pinch of cinnamon or splash of vanilla extract can also be used to add some sweetness back into your over-extracted coffee.
If the coffee tastes more sour or sharp then it’s under-extracted. This is because the coffee hasn’t been in contact with the water for long enough for the complex carbohydrates to start breaking down into simple sugars. This can be due to your brew time being too short, the water not being hot enough, or from using too coarse a grind setting for your brew method.
If your coffee seems to feature all of these bad flavors then you may have a mixed bag. Some of the coffee is under- and some is over-extracted. This is most likely due to an uneven grind which is very common with blade coffee grinders. To avoid this, always use a burr grinder to ensure an even grind consistency.
Some Tips to Improve Extraction When Brewing Coffee
Here are a few tips to help improve your extraction when brewing:
- Grind coffee to the correct consistency. To help optimize the extraction for your next cup of coffee, start by ensuring the coffee is ground to the correct consistency for your brew method. Use a good quality, burr grinder and research the coarseness you need for your coffee maker.
- Use filtered water at the correct temperature. Add the correct amount of coffee for your brew method and, using filtered water, heat this to 195-210°F (91-99°C). Ensure the coffee is fully saturated in hot water and let it sit for 30 seconds before you pour the rest of the water over it. This is called the bloom stage and helps release excess CO2 so reduces the acidity of your coffee.
- Brew your coffee for the proper amount of time. Make sure your coffee has enough time to brew fully, but don’t let it sit too long! If you’re reheating the coffee later on, make sure you don’t warm it up above 205°F (96°C) otherwise you will burn it. Keep an eye out for coffee makers with a glass carafe and heat plate as these can overheat the coffee after brewing and end up burning it. This is enough to ruin your coffee even if the extraction stage went well. If you’re worried about this but you want to keep your coffee hot then consider transferring it to a pre-heated thermal carafe to enjoy later on.
The Bottom Line
Brewing a beautifully balanced cup of coffee isn’t always the easiest thing to do as there are so many factors that can affect the extraction of flavors from your coffee beans. Once you understand a bit more about these factors though you are ever closer to brewing coffee that’s extracted to perfection. I hope this article has been helpful in pointing out where you can improve your coffee game and I’d like to wish you the best of luck with your next cup of joe. Happy brewing!