Pitching yeast and fermentation

What you need

• Yeast that suits the beer style
• A sanitised fermenter with an airlock
• A thermometer, ideally a fridge with a temperature controller
• A hydrometer or refractometer

Step by step

1. Step 1Prepare the yeast

   You can sprinkle dry yeast straight onto the wort or rehydrate it for 15 minutes in a little boiled water cooled to 25 °C (77 °F). Bring liquid yeast to room temperature first.

2. Step 2Pitch the yeast

   Add the yeast to the aerated wort as soon as it is at the right temperature. For 20 litres (about 5.3 gal) of beer of normal gravity one 11 g (0.39 oz) packet of dry yeast is usually enough. For strong beers or lagers use two.

3. Step 3Hold the temperature

   Ale yeast usually ferments at 17 to 21 °C (70 °F), lager yeast at 9 to 12 °C (54 °F). Fermentation makes its own heat: the beer is often 2 to 4 °C (39 °F) warmer than the room.

4. Step 4Watch the main fermentation

   After 12 to 48 hours a foam forms, the krausen, and the airlock bubbles. Main fermentation usually takes 3 to 7 days for ales, longer for lagers.

5. Step 5Measure the final gravity

   After a few days, measure the gravity. If it stays the same for two to three days, fermentation is done. Bubbling alone is not a reliable sign.

6. Step 6Let it condition

   Leave the beer on the yeast for a few more days after fermentation. The yeast cleans up off-flavours such as diacetyl, which tastes of butter. For lagers a diacetyl rest helps: 2 days at 15 to 18 °C (64 °F) at the end of fermentation.

7. Step 7Bottle or dry hop

   After that you can dry hop the beer or bottle it straight away.

Tips and common mistakes

• Beer fermented too warm often tastes of solvent or fusel alcohol. Better ferment at the lower end of the range.
• Open the fermenter as rarely as possible. Take samples with a sanitised siphon or from the tap.
• If fermentation stops too early: move the fermenter somewhere a little warmer and gently swirl it to rouse the yeast.