Extraction, in the context of brewing coffee, is the bringing out of microscopic particles from coffee grounds into water. To understand the process, we need to revisit high school chemistry (sorry!). When you brew coffee, you’re creating a solution. Tiny particles from the coffee grounds, or solutes, are dissolved in water, the solvent. You might also remember that there are five things that impact how strong a solution is:
- the ratio of solutes to solvent
- the size of the solutes
- the temperature of the solvent
- the duration of time the two substances are mixed
- how much the solution is agitated
We’ll examine how each of these factors impacts extraction when brewing coffee, using as little chemistry jargon as possible. To understand their effect on the brewing process, we should first look at what an ideal coffee solution is.
The Goal Is To Achieve 18 to 20 Percent Extraction
Roughly 30 percent of coffee is soluble in water, but this is not an ideal target. Coffee tastes best when it is 18 to 20 percent extracted. Thankfully, you don’t need a chemistry lab to determine your coffee’s extraction. Anything below this sweet spot will taste sour, and extraction above 20 percent will be bitter. If you hit the 18 to 20 percent mark, your tastebuds will be able to tell. It will be sweet and delicious.
The Coffee-to-Water Ratio Should Be Between 1:16 and 1:18, And Should Be Kept Constant
The ratio of coffee (solute) to water (solvent) will significantly affect your brew’s flavor. Too little coffee in too much water will taste thin and weak. Too much coffee in too little water will not produce a better cup, though, because the amount of soluble coffee that the water can hold is finite.
Your coffee-to-water ratio should be kept constant, not used as a means for correcting under- or over-extraction. The best way to ensure a proper, consistent ratio is with a Specialty Coffee Association of America (SCAA) scoop, which will measure 10 g. Alternatively, you can use a kitchen scale, which can also measure your water.
Finer Grind Speeds Up Extraction, While Coarser Grind Slows It Down
The grind setting used determines the size of the coffee particles (the solutes), which impacts how quickly they are extracted. A finer grind increases the surface area of the coffee, thus speeding up extraction. A coarser grind is used for brewing methods with a long dwell time, because it slows down extraction.
Different brew methods have different recommended grind settings, but you may want to experiment to find your preferred setting. Whatever you settle on, the grind used should be a consistent size; having small and large coffee grounds in the same brew will lead to under- and over-extracted particles.
Ideal Water Temperature Is Between 195 and 205 F
The temperature of the water (the solvent) affects how much it can extract from the coffee grounds. Water is a better solvent at higher temperatures, which is why hot brewing methods use near-boiling water. For most brewing methods, the water should be between 195 and 205 degrees Fahrenheit.
(Full batches of coffee taste better than partial ones on auto-drip machines because the machines are designed to bring a full pot of water up to the proper temperature.)
Although you want to use hot water, coffee shouldn’t be kept warm with a hot plate. Introducing an external heat source will overcook the coffee and create a burnt taste. Instead, coffee will taste better if it is kept warm in a thermal carafe. These use the coffee’s heat to keep it warm, so they don’t burn it.
Contact Time Determines How Much Is Extracted, And Varies By Brewer
How long coffee brews for will determine how much is extracted, since the process takes time. The longer grounds and water are in contact with each other, the more coffee will be extracted. Each method has a recommended brew time. Check the brewing instructions below to find the recommended duration for your preferred method.
Agitation Increases How Much Grounds Mix With Water
Agitation increases how much the grounds mix with the water, thereby affecting the speed of extraction. Simply pouring water over grounds agitates them, and in some methods this is enough agitation. Immersion brewing methods, such as a French press, however, should be agitated during the dwell time so that all the grounds are evenly extracted.
Few people think of all the chemistry that is involved in brewing coffee, especially when making a cup or pot early in the morning. The entire process is a chemical process, though, and each of these factors will affect how your final outcome tastes. Until you find that sweet spot of 18 to 20 percent extracted, keep adjusting one variable at a time. Eventually, you will brew the perfectly extracted cup of coffee.