Have I ever mentioned that managing fermentation is really important to making great beer? Sure I have. And I know that one of the biggest challenges to most home brewers is controlling fermentation temperature. Well, maybe you don’t have a dedicated fermentation chamber but you can certainly make sure that you pitch the correct amount of yeast. Unfortunately, much like IBU calculations, figuring out the correct yeast pitch relies on a bit of guesswork. Still, a little knowledge can be a good thing.
First, how much yeast is needed? The simplest number is about 1 million cells per milliliter of wort per degree Plato. A more detailed recommendation is pitching 750,000 cells per ml per °P for ales and 1.5 million cells per ml per °P for lagers. For ease I am going to use the 1 million value. A 5 gallon batch is 18.9 liters or 18,900 milliliters. This means that we need 18.9 billion cells per degree Plato. So for a beer at 10 °P (1.040) this means that 189 billion cells are needed.
The challenge for the brewer is that your basic White Labs tube or Wyeast smack pack only promise 100 billion cells. Despite any claims of being “pitchable” the volume of cells in these packages are not truly sufficient, one needs about twice as many yeast cells. The easiest way to double the volume of yeast cells is to pitch either a White Labs tube or Wyeast pack into make a one liter volume of wort and let it ferment out.
Here is an easy solution: get some empty two liter soda bottles, wash them and sanitize with your favorite sanitizer. Add one liter of wort and and the yeast, and cap the bottle. Shake like crazy, then crack the cap and squeeze the bottle until the liquid is near the top. Set in a nice warm place and let it do its thing. The great thing about 2 liter pop bottles is that they are incredibly strong. Once the yeast begins to work and liberates some carbon dioxide, the bottles will become quite firm to the touch.
Cracking the lid allows some of the CO2 to escape, and you can once again squeeze the bottle before resealing. Shake again to redistribute the yeast. it makes a great substitute for a stir plate. And, when the yeast has finished growing you can put the whole bottle into the fridge until it is needed. it is safe, sealed, and secure.