PITCHING RATE BASICS WHAT’S THE DEAL ABOUT PITCHING RATES?
Whether you are brewing 5 gallons or 500 barrels, the number of living yeast cells introduced at pitching is critical for proper fermentation performance. Every wort, fermenter, oxygenation system, and yeast strain is different, so most brewers agree that “hitting it out of the park” is best way to avoid incomplete fermentations. The number of living cells/ml in a liquid starter culture is determined by RBY labs and is shown on each label. RBY labs suggests over 100 billion cells/5 gallons for low gravity fermentations, and over 200 billion cells/5 gallons for gravities higher than 1.060. This translates to 5 million cells per ml for low gravity worts under 5% ABV, and 10 million cells per ml for higher gravity beers.
BIOLOGY BEHIND THE PITCHING RATE
If pitched at a low rate, yeast cells spend too much energy dividing, and can flocculate out early. If pitched at a higher rate, the yeast directs more energy toward turning over the carbohydrates and nutrients in the wort, and making the desired CO2 and ethanol instead of dividing. The transition between aerobic and anerobic fermentation takes time and energy. Also, oxygen is required for essential sterols and unsaturated fatty acids required for alcohol tolerance. That is why shaking or oxygenation of wort prior to pitching works so well because it buys more aerobic energy before the yeast start transitioning to the anaerobic state.
IT IS A BIG DEAL.
If you have problems controlling fermentation conditions (especially temperature), oxygen, or supplement your brewing with simple sugars, use more yeast to be safe. If in doubt, buy 2-3 RBY 5 gallon pitches for each five gallons to ensure proper yeast performance.