One jar of ale or lager yeast contains approximately 2 billion active yeast cells. For fermenting larger volumes of wort, it is necessary to propagate the yeast. Saccharolicious recommends the following procedure for 20 l 1,048 (12°P) wort*:
- Add a small volume of sterile wort or water to the jar. Close and shake thoroughly to dislodge the yeast from the agar slant.
- Pour the yeast suspension in 500 ml sterile wort (1,040 pr 10°P) and let grow for 24 h at room temperature
- Pour the starter from step 2 in 1 l (when using a magnetic stirrer) or 2 l sterile wort and grow for 24 h.
- You now have enough yeast to ferment 20 l standard strength wort. Either pour in the whole starter, or let the yeast settle in the fridge and decant the starter before pitching yeast.
Do you prefer smaller starter volumes and more steps? Are you making a big beer? Do you want to propagate bigger volumes? Have a look at following pitching rate calculators, or throw us a question via mail or facebook.
For instructions on making you own magnetic stirrer, have a look at instrucatables.com or at online forums. You can also find stirrers on ebay, and even some homebrew stores sell them.
*Please note that actual yeast counts can vary depending on storage time, starter wort density and nutrient level, efficiency of the stirrer, etc. If your beer has not fermented ready within a week, bigger starter volumes might be necessary using your system.