What is coffee extraction?
Coffee consists of 70% of wood fibers, which are not water-soluble. The remaining 30%, however, are water-soluble. During coffee extraction, water-soluble components (aromas, fats, bitter substances, acids, and minerals) are removed from the coffee grounds with the help of water. The extraction describes an extract of soluble parts from a solid substance. You will not achieve the best taste result in the cup with the complete 30%, but if only 18% – 22% is extracted, then you will. The balance between bitterness and acidity is most balanced and you can taste a certain sweetness. The balance between acidity and bitterness can thus be determined with the extraction rate.
Example of extraction rate: With an extraction rate of 20% and an amount of ground coffee of 18 g used, 3.6 g of substances (= 3.6 g positive coffee aroma) is released from the coffee.
Extraction rate of 18% – 22%
In the 1960s, the Coffee Brewing Center in the USA commissioned a study to determine the coffee extraction preferences of users of filter coffee. The data obtained from the Coffee Brewing Center indicate ideal coffee extraction if between 18% and 22% of the ground coffee is dissolved in hot water. This “correctly brewed” coffee specification has been adopted by several international coffee associations, including the Norwegian Coffee Association (NCA) founded in 1975, the Specialty Coffee Association of America (SCAA) founded in 1982, and the Specialty Coffee Association of Europe (SCA) founded in 1998 ). The extraction rate of 18% – 22% has become a global standard.
The extraction rate is critical to a balanced drink
An espresso tastes ideal when the balance between bitterness and acidity is most balanced. The balance between acidity and bitterness can be determined with the extraction rate, which can be measured using a refractometer. The extraction rate gives you information about how many ingredients from the ground coffee were released from the coffee during the brewing process. If this is below 18%, one speaks in the technical jargon of under-extraction. In this case, the coffee/espresso is acidic and the aromas are underdeveloped. An under-extracted coffee/espresso is particularly lacking in the body. If the extraction rate is greater than 22%, one speaks of over-extraction. The filter coffee or espresso becomes bitter, unpleasantly intense, and sometimes even burnt. In this case, too many (unpleasant) ingredients were extracted from the coffee bean.
Extraction rate? Is it that important?
We can understand if the topic of extraction rate seems a size too big at the beginning of your career as a home barista and you don’t want to deal with it – after all, it’s all about the preparation of a drink. But it is worthwhile to deal with it because the extraction rate is responsible for whether a coffee/espresso is a success or a failure from a “scientific” point of view. So if you are unsure whether your coffee/espresso is good or bad, we recommend purchasing the VST LAB Coffee Refractometer for baristas (Price: approx. $1k). Sure, you don’t make such an investment every day. But with the help of a refractometer, you get absolute control. Besides, it allows you to calibrate the various components during espresso preparation so that you are suddenly very close to your perfect coffee/espresso.
Guidelines for an ideal extraction even without a refractometer
If you don’t have a VST LAB Coffee Refractometer, you can follow simple guidelines that will help you combine brew strength and extraction rate to extract a harmonious drink. You need a digital scale for this, with which you can determine the amount of ground coffee and the amount of water / filling amount.
The following guide value applies to the preparation of filter coffee: One liter of water is poured onto 50 – 60 g of ground coffee.
When preparing espresso, the guideline value can be described using the brewing ratio. The standard brewing ratio is 1: 2. For every gram of ground coffee, two grams of espresso are extracted, so for example 18g of ground coffee should be 36g of espresso. With the requirement to extract your espresso with a brewing rate of 1: 2, you will likely get into the range of the above extraction rate of 18% – 22%.
The guideline values mentioned give a direction – nevertheless, they do not give you any guarantee that the preparation of the drink will really work out perfectly.