The three controllable variables
At its core, espresso is physics and chemistry. Three parameters define the result:
- Ratio: coffee dose to liquid out
- Temperature: brew-water temperature
- Time: shot time in seconds
The ratio: 1:2 as a starting point
18 g coffee → 36 g liquid = 1:2 ratio. Not a dogma, but a proven starting point. Ristretto (1:1.5) is more intense, lungo (1:3) lighter. Without a scale you're working blind.
Temperature: 90–96 °C, depending on the roast
Lighter roasts need higher temperatures (93–96 °C), darker roasts lower (88–92 °C). Too low → sour. Too high → bitter.
Shot time: 25–30 seconds
From first drops to stop, a double shot takes 25 to 30 seconds. Faster = under-extracted (sour). Slower = over-extracted (bitter).
Quick diagnostic:
Sour + thin = under-extracted → finer grind, higher temperature
Bitter + dry = over-extracted → coarser grind, lower temperature
Watery with otherwise OK flavour = ratio too high (too much water)
Sour + thin = under-extracted → finer grind, higher temperature
Bitter + dry = over-extracted → coarser grind, lower temperature
Watery with otherwise OK flavour = ratio too high (too much water)
First steps, one at a time
- Grind 18 g coffee (double basket)
- Distribute evenly with a distributor
- Tamp at about 15–20 kg of pressure (flat, vertical)
- Start the timer when the pump starts
- Stop at 36 g liquid (target: ~27–30 s)
Too sour? Grind one notch finer. Too bitter? One notch coarser. Change only one variable at a time.