Extraction is how much of the coffee dissolves into the water. Changing extraction changes the balance of flavour compounds. A short extraction can taste sharply sour; extending it may improve balance, but the result also depends on the coffee and how evenly water passes through it. Specialty coffee has long used a target of about 18 to 22 per cent of the coffee's weight dissolved, and espresso is usually treated the same way. It is a guide, not a rule, and you can taste your way to it without any equipment other than a scale.
Start with a recipe you can repeat
Weigh everything. For a first attempt on a standard double basket:
- Dose: 18 g of ground coffee in the basket.
- Yield: about 36 g of espresso in the cup (a 1:2 ratio).
- Time: about 25 to 30 seconds from starting the pump.
- Water temperature: about 92 to 94°C, if your machine lets you set it.
If the first shot tastes balanced, you are done. If it does not, use the steps below.
Fix sour
A sour shot tastes sharp, thin, salty or like lemon juice with little sweetness. It often runs fast, under 20 seconds.
1. Grind finer. This slows the water and extracts more. 2. If it is still sour, increase the yield a little, for example 38 g instead of 36 g. 3. Check your temperature is not too low, and that the machine is fully warm. A cold group head under-extracts. 4. Check the coffee is not too fresh. Coffee in its first days after roasting releases gas that disrupts extraction, so wait about a week for espresso. 5. If you are using a very light roast, expect to need a finer grind and a hotter brew.
Fix bitter
A bitter shot tastes harsh, drying and burnt, and the finish lingers unpleasantly. It often runs slow, over 35 seconds.
1. Grind coarser. This speeds the water and extracts less. 2. Reduce the yield, for example 34 g instead of 36 g. 3. Check the dose. Too much coffee in the basket slows the shot. 4. Check the coffee itself. Dark roasts taste bitter by nature. If you want less bitterness, choose a medium roast. 5. Clean the machine. Old coffee oils on the group head and basket add bitterness.
The other things that matter
- Distribution and tamping. If the water finds easy paths through the coffee (called channelling), some of it is under-extracted and some is over-extracted at once, which tastes both sour and bitter. Level the bed before tamping, and tamp level.
- Freshness. Coffee roasted two to four weeks ago usually tastes best. Older coffee tastes flat.
- Water. Very hard or very soft water changes extraction. If you can, use filtered water, and descale your machine on schedule.
- Your grinder. A blade grinder cannot make a consistent espresso grind. A burr grinder is the biggest upgrade you can make.
Change one thing at a time
The most common mistake is changing the grind, the dose and the yield together. Change one variable, taste, then change the next. Keep notes: dose, yield, time and what it tasted like. After a week you will see a pattern.
Not sure whether it's sour or bitter?
Sometimes it is both: the shot is sour at the front of the mouth and bitter at the back. That is usually uneven extraction. Check your distribution first.
Learn it hands-on
Our Espresso fundamentals class works through exactly this on commercial machines, with an instructor. You can also bring a question to the bar at any café, and the barista will talk it through.