Extraction rate. What is it? Well, it’s a technical term, but when understood, can lead to getting the best results from your coffee. And coming to that understanding involves breaking apart how coffee grounds react with water depending on the coffee’s grind size. Having a finer grind size results in more surface area for water to extract flavor from the coffee, but having a grind size that is too fine, might result in over-extraction.
How do we know when our coffee is over or under-extracted? That’s where we use extraction rate. In coffee, the rate of extraction is measured by the percentage of the grounds that get dissolved in the water. It’s basically how much coffee is extracted in the brewer and ends up in your cup or in barista hustle’s words: “Extraction is everything that the water takes from the coffee.”
According to theperfectdailygrind.com, compounds that are extracted into your brew have a direct impact on the flavor and even the aroma of the coffee. Coffee typically contains water-soluble compounds that produce, bitter, acidic, and sweet flavors.
Since coffee compounds are not all extracted at the same rate, you need to find the perfect balance in your brewing time. Usually, fruity and acidic notes are extracted first. This means if your cup is under-extracted, it might become acidic. It’s followed by sweetness and balance, and then finally bitterness.
But let’s get a little bit more technical, how do you compute for extraction rate or extraction yield? Here’s a formula from www.baristainstitute.com: Extraction Yield % = Brewed Coffee (g) x TDS (%) / Dose (g).
Brewed coffee is the amount of liquid coffee that ends up in your cup, TDS is an abbreviation of “Total Dissolved Solids.” You’ll get best results by reading this using a digital meter (pictured.) TDS ranges from organic matter such as calcium and magnesium, which basically contributes to the strength of your coffee, and dose means the amount of ground coffee you put in the brewer.
So if you are brewing with 18g of coffee, and your espresso coffee is at 36g, the extraction yield % of my cup is at 20%. (36 g x 10 % / 18 g = 20 %)
It seems difficult to comprehend but it’s actually easier when you experiment with your coffee to taste the difference that a little more extraction makes. We recommend playing around with your grind size, to get a better gauge of which output you prefer and how you are maximizing your coffee.