Coffee Nerd: Extraction
Coffee extraction, simply put, is using a combination of water, temperature, pressure and the length of water coffee ground contact time to bring out the soluble contents (and sometimes insolubles such as fines) into the cup. The word extraction is often used when we talk about the amount and type of chemical compounds that are brought out from the coffee in all brewing methods. Extraction is a controllable process that determines the taste of the final yielded liquid through manipulating different variables. These variables may be brew ratio, water coffee contact time, water temperature etc. These elements all affect the flavour and aroma.
Different compounds have different solubility and contribute to different flavours (sweet, sour, salty and bitter) and aromas. In order to be able to manipulate the flavour profile of an extraction, it’s crucial to first understand which compounds dissolve in what timeframe and under which conditions. It is an extremely complex process with much scientific research conducted in order to understand it more thoroughly.
Broadly speaking, compounds that contribute to acidity or sourness get extracted first. Heavier compounds that contribute to bitterness come later. When you have a very fast extraction (short water contact time or coarse grind), the coffee tastes sour. When you have a very slow extraction (long contact time or fine grind) the coffee tastes bitter. Dial in a coffee means finding balance of those flavours and maximising sweetness, which lies somewhere in between. This process does involve some trial and error. A skilled barista should be able to do this quickly and without much waste.
Extraction is a rabbit hole of information and a developed art. It’s about trying to get that perfect balance in flavour and aroma of the coffee. There’s a lot more to a cup than meets the eye.
Words by our roaster Daniel Shi