Understanding Espresso Extraction

What is extraction? Extraction is the process of dissolving soluble compounds from ground coffee using hot water under pressure. The goal is to extract the right amount — not too little (under-extraction, tastes sour) and not too much (over-extraction, tastes bitter). The key variables Extraction is controlled by: grind size (finer = more extraction), dose (more coffee = slower extraction), water temperature (higher = more extraction), pressure, and brew ratio (how much water you use relative to coffee). Adjusting one variable changes all the others, which is why dialling in requires patience. Brew ratio: the starting point A standard double espresso uses a 1:2 ratio — 18g of coffee in, 36g of liquid out. This is a good starting point for most coffees. Specialty roasters may recommend ratios anywhere from 1:1.5 (ristretto) to 1:3 (lungo). Always weigh both your dose and your yield. Reading the shot A good shot runs evenly, starts honey-coloured, darkens to deep brown, and finishes before it turns pale and watery. If the crema disappears quickly or the shot looks watery, it is probably over-extracted. A short, fast shot with a sour taste is under-extracted. Temperature matters Most home machines are pre-set around 92–94°C, which suits medium roasts. Light roasts often benefit from slightly higher temperatures (94–96°C) to extract fully. If your machine allows temperature adjustment, experiment in small increments.