Making a Yeast Starter
Step 1Boil 1 Litre of water and stir in 1/2 cup (125 ml) of dark or light dried malt extract This will produce a starter of about 1.040 OG. Boil for 10 minutes, adding a little bit of hops if you want to replicate a pre-fermentation wort. Put the lid on the pot for the last few minutes turn down the heat to a gentle simmer then turn off the heat and let it sit while you prepare for the next step. Adding a quarter teaspoon of yeast nutrient to the starter wort is also advisable to ensure good cell growth.
Step 2Time to cool the starter wort. Fill the kitchen sink with a couple of inches of cold water. Add ice cubes if handy or ice packs to chill the water as well. Take the covered pot and set in the sink of icy cold water moving it around periodically to speed up the cooling. When the pot feels cool, about 27C or less, pour the wort into a sanitised glass jar or growler or flask or something similar. Pour all of the wort in, even the sediment. The sediment contains protein and lipids which are beneficial for yeast growth at this stage of their lifecycle.
Step 3Pour the wort into a sanitised glass container (flask, growler, etc.) and pitch the Yeast. Cover the top of the container with a sanitized piece of aluminum foil so that it is flush with the container, but will still allow C02 to escape. Vigorously shake or swirl the container to get as much oxygen as possible dissolved into the solution. Keep the starter at room temperature for 12 -18 hours on a magnetic stir plate if you have one, or occasionally shaking it to keep the solution aerated. You probably will not see any visible activity, but the Yeast is busy taking up the oxygen and sugars in the solution and growing new cells. After 18 hours, the yeast will have consumed all of the nutrients and oxygen in the starter. Switch off the stir plate or discontinue shaking it and it will form a milky white layer on the bottom of the container as the yeast flocculates (falls out of the solution). If you are not planning on pitching the yeast right away, you can store it in the fridge with the foil still in place.
Step 4When you are ready to brew, decant off most (80%) of the clear liquid from the top, carefully so as not to disturb the yeast layer below. Once the yeast and your wort are approximately at the same temperature, rouse the starter yeast into suspension with the remaining malt solution and pitch the yeast slurry into your wort. Time to #BrewHappy - cheers! Typical Starter Volumes for 19 Litres (5 US Gallons) of wort:
- To activate the Yeast: 500 mL water with 1/4 cup (65 ml) of dried malt extract
- To revitalise Yeast past its Best Before Date: 1 Litre of water with 1/2 cup (125 mL) of dried malt extract
- To brew a high gravity beer: 1 Litre of water with 1/2 cup (125 mL) of dried malt extract
- To brew a lager beer, starting fermentation at 10 - 12 C: 2 Litres of water with 1 cup (250 mL) of dried malt extract
Here is a great little video to help show you how to make a Yeast Starter