November 22, 2018

Coffee Extraction & How It Helps Create The Perfect Cup

Are you looking to improve your cup of coffee? It might be easier than you think. By understanding coffee extraction, you can better control the acidity, sweetness, and balance in your brew and get your perfect cup every time.

Read on to better understand why you should care about grind size, water temperature, and bed depth.

You may also like Why Are Some Coffees More Acidic Than Others? A Brew & Roast Guide

Coffee served on a chemex

Freshly brewed pour over coffee. Credit: Andreas Palmer

What Is Extraction?

Extraction is simply the method by which we dissolve flavours and other components from roasted and ground coffee. As coffee is brewed, hundreds of unique compounds are extracted from the ground beans into the water, making your daily cup.

The compounds that are extracted have a direct impact on the flavour and aroma of the coffee. Extracted coffee typically contains the following water-soluble compounds, among many others:

  • Caffeine (bitter)
  • Acids (some of which create sour and/or sweet flavours)
  • Lipids (viscosity)
  • Sugars (sweetness, viscosity)
  • Carbohydrates (viscosity, bitterness)

By controlling how these compounds are extracted, we can have more control over the profile of the cup.

Coffee brewed on a Clever. Credit: Anshu A

How Does Extraction Affect Taste?

Coffee compounds are not all extracted at the same rate. Fruity and acidic notes are extracted first, followed by sweetness and balance, and then finally bitterness.

Under-extracted coffee won’t have the sweetness and slight bitterness needed for balance, and will have a sour taste. An over-extracted brew will taste bitter, as the compounds that create sweetness and acidity will be overwhelmed. You can create coffee that is balanced to your taste by controlling the extraction.

freshly brewed coffee in v60

Pour over coffee brewed on a V60 using a cloth filter. Credit: Rawpixel

What Is The Perfect Level of Extraction?

You may hear about extraction percentages and the ideal extraction level of Total Dissolved Solids (TDS). This is simply how much “stuff” has been extracted from the coffee into the water and tends to be around 18–22%.

But remember that each coffee has a different character. Rather than aiming for a specific “perfect” number, focus on getting the highest percentage extraction at which the coffee still tastes good to you.

You may also like Coffee Science: What Is TDS And Why Should You Care?

coffee brewed on french press

Coffee brewed using a French press. Credit: Rachel Brenner

How To Control Extraction

To get the best flavours from a coffee, you need the right level of extraction. Understanding how this happens can allow you to troubleshoot if your coffee doesn’t taste right.

Is it too sour? It could be under-extracted and you are tasting more acid than other compounds. Try a slower brew or finer grind.

Is it bitter? The coffee may be over-extracted. Try a larger grind to slow down extraction or brew for a shorter amount of time.

You also want to avoid inconsistent extraction. This means that some grounds are extracted more quickly than others, leading to a mixture of under-extracted and over-extracted grounds. This is a problem because you won’t be able to control or replicate the final flavour profile.

coffee grounds ready to be brewed

Coffee grounds ready to be brewed using a Kalita Wave. Credit: Devin Avery

You can tweak extraction to compensate for less-than-ideal factors. If your beans are a little stale, try grinding them more finely to allow quicker extraction and more lively notes from different compounds.

Dark-roasted beans are more soluble because they have been exposed to heat for longer. Keep in mind that they will extract more quickly than light-roasted beans and consider using a coarser grind if you’re switching to a darker roast.

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Coffee in a carafe. Credit: Sebastian Franzén

Variables That Influence Extraction

Solubility and extraction can be affected by a coffee’s genetic characteristics, which is out of our control. But we can adjust others. Let’s take a look at how each factor affects extraction and profile.

Grind size is important, as extraction is quicker with finely ground coffee than with coarse, exposing more surface area. This can increase bitterness because compounds can extract too quickly. A coarse grind size means more acidity, which can create a weak, flat cup as it extracts fewer flavourful compounds.

Freshly ground coffee. Credit: Coffee and I

It’s also more compact, creating less room for the water to trickle between the grounds. It can increase brewing times for pour over and filter coffee. Smaller grounds can extend brew time and providing more extraction opportunities.

Fine grounds are also more easily displaced by water. Take time to ensure they don’t sit unsoaked, on filter instead of being saturated. Choose your grinder carefully as lower-quality ones can produce “fines”, which are tiny bean fragments that create a muddy brew if not filtered out. Because they’re so small, they extract quickly, creating an undesirable flavour.

Brew method is another important factor. The longer the brew, the more extraction time. Generally, short brews are more acidic and longer ones more bitter.

An espresso has a short brew time and uses pressure to force water through densely packed coffee. It’s suited to a finer grind size, allowing water to flow easily and creating more surface area for extraction. A French press is a longer brew, so it’s common to use a coarser grind to slow extraction and avoid bitterness.

You can adapt an espresso brew time by seconds either way, which will impact extraction. You can also change the brew time to compensate.

A barista brewing coffee. Credit: Kinima Coffee

Water Temperature & Quality

The “ideal” water temperature to make coffee is around 195–205℉ (around 91–96 ℃). This is just under boiling and is the point at which most flavour compounds easily dissolve in water.

The higher the temperature of the water, the more quickly extraction will happen. If water is too cool, extraction takes much longer. At a certain point, some compounds simply won’t extract. This is why a cold brew takes much longer and has a much more mellow flavour than a hot brew of the same beans.

barista pouring coffee from french press

The Specialty Coffee Association has recommended water standards, but the bottom line is that it should be pH neutral and free from contaminants that could affect flavour.

Hard water contains minerals, which can help extraction. Magnesium aids in the extraction of fruity, sharp flavours and calcium enhances creamy notes. But if there are too many minerals in the water, they can reduce the amount of extraction and affect flavour.

Commercial espresso machines include a water filter. If you’re not confident in your tap water, try using filtered or bottled water and see if you can taste a difference.

Bed Depth

Pour over and batch brewing methods involve pouring water through a coffee bed. The important thing with bed depth is consistency. Unevenly piled or unevenly soaked grounds will create channels through the grounds, extracting more coffee here. Water always takes the route of least resistance, which is why we use dense coffee pucks.

carafe of freshly brewed coffee

Freshly brewed filter coffee. Credit: Fernando Pocasangre

Pouring water too quickly or in an irregular motion can displace grounds so they sit dry or not fully soaked on the filter, above water level. It happens often with fine grinds and when you pour directly into the bed’s middle. Omitting some grounds means that not all th coffee is extracted and your method is inconsistent. Prevent it by starting with an even bed of grounds and consider pulse pouring or agitation to evently saturate all the grounds.

Be mindful of your bed depth. A shallow bed may allow water to pass through too quickly to allow much extraction. A very deep bed may keep the water and coffee in contact for too long, leading to over-extraction.

A barista pours water into a Chemex pour over device.

A barista brews with a Chemex. Credit: Michel Chateau

Extraction balances many variables. Adjusting one factor will impact the others. Understanding extraction will allow you to better control your coffee profile and tweaking variables can expose new flavours to explore. When you have a method that works for you, try to replicate the variables as closely as possible each time.

Or use it as a basis to start a whole new experiment. Consistent extraction is the key to making delicious coffee, but you don’t need to have the same profile each time. Don’t be afraid to change your technique to bring out the best in each new coffee.

Enjoyed this? Check out Understanding Coffee Extraction & Other Key Brewing Concepts

Perfect Daily Grind

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