When we go to brew coffee in the morning we’re dissolving water soluble compounds from the coffee bean into the water. We call this process extraction, and while it’s quite a simple concept it can be tough to get right. Over the last sixty or so years our understanding of extraction has gone from very little, to a thorough but ever evolving picture of what’s happening when coffee and water interact. The goalposts always remain the same though, making something delicious.
We’re going to overview what we know about extraction to pull back the curtain a little bit, so that tasty coffee is more consistently achievable.
About 28% of the coffee bean is water soluble, meaning it gives up its flavor in water. That other 72% is cellulose, the structural unit of the coffee bean. Think of it as the weight bearing walls and posts that houses the coffee flavor. The goal of brewing is simple: to dissolve desirable compounds into the up, and to leave behind the less desirable.
While there are ways to measure extraction, tools are expensive and are best left to research labs and quality control programs of high-volume cafes and production facilities. The best tools we have are our palates. So how do we tell if a coffee is properly extracted?
Under–extraction occurs when we haven’t dissolved enough compounds out of the coffee. The most dominant flavors when this is the case are sourness and saltiness. This is because the first things that dissolves when coffee and water interact are the acids and the salts. If your coffee is reminding you of Sour Patch Kids then it is likely under–extracted.
Over-extraction is the other end of the spectrum in which we have pulled out more than the desirable number of compounds from the coffee. If you notice a dominant bitterness, and a drying and papery finish then it’s an indicator that your coffee is over-extracted.
Ideal extraction is like goldilocks. It’s just right. Not too sour, not too bitter. Well brewed coffees are typified by sweetness – the sugars present in the coffee seed have been broken down in the roasting process and dissolved into our cup! There’s acidity, but not too much. Bitterness can be present, but like a well-made cocktail or a good dark chocolate it’s balanced with the rest of the flavor components.
|Under-extracted ——————–||Ideal extraction ——————-||Over-extraction|
The above table should be thought of as a spectrum. When we make coffee, we can manipulate our brewing variables in order to move in different directions. The three main elements that control extraction are the brew ratio, the grind setting, and the brew time.
The brew ratio is the ratio of coffee to water, expressed by weight. Our typical ratio is 1:16, coffee:water. To change the level of extraction we can increase or decrease the amount of water used, while keeping the dose of coffee consistent. (check out our recent blog with more on ratio here) By changing the ratio we are also adjusting the strength of our brew. When we think of strength we often think intensity, or amount of caffeine, both of which are true, but in this case we mean the concentration of dissolved particles in the resultant cup.
The grind setting affects how quickly coffee gives up flavor, with finer coffee brewing faster and coarser coffee needing more time to extract fully. It’s the fine grind that allows espresso to brew so quickly, while the coarser grind that requires a French press to brew for 4 minutes. If we notice coffee tasting sharp and sour it could be too coarse and fining the grind will help it extract more fully.
With brew time it’s simple. More time, more extraction, and less time, less extraction. In filter brew methods brew time is linked to grind setting. This is because the grind setting controls the flow rate for any pour over or batch brewed coffee. It follows then, that a finer grind will both extract more because of the smaller particles and slow down the water causing the brew to take more time. Both factors promote more extraction; it’s like doubling down on trying to get more flavor out of the coffee. The inverse is true if we adjust the grind coarser.
Imagine we brew a coffee at a 1:15 ratio and it tastes puckeringly sour. By the above table, we’re on the left side of our spectrum, and we know we need to extract more. We try again after adjusting the grind quite a bit finer while keeping the other variables the same, and in our second brew the sourness is gone but it’s replaced by an empty and drying flavor. We went too fine into over-extraction territory. To correct we coarsen the grind slightly. The next brew is sweet and balanced, but a little bit heavy in mouthfeel. Happy with the grind setting, we decide to change the ratio and adjust it from 1:15 to 1:17. The body is lighter, and the extra water helped extract more and bring even more sweetness and balance to the coffee!
Have a question or a topic you’d like to see covered? Shoot us an email at [email protected], or tune in to the livestream Wednesdays at 10:30am, Brian will be taking questions in the chat!