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In brief, the purpose of this calculator is to calculate yeast pitching rates based upon the manufacturer's pitching guidelines. The values for repitching harvested yeast are also provided for comparison purposes.
The estimates for the right amount of yeast to pitch seem to vary widely. Some publications (White and Zainasheff, 2010, p. 122 - 123; Hyde, 2018) and online calculators use formulas such as .75 million cells/mL/degree plato to calculate the pitching rate. The MrMalty.com web site has a good description. A general goal from this approach is to have about 175 to 200 billion ale yeast cells per five gallons (19L) for ale yeast. In contrast, the pitching rates suggested by yeast manufacturers seem much lower. For example, the Lallemand pitching calculator recommends that 50 billion cells of Nottingham are needed for a five gallon (19L) batch at 1.050 SG.
So why would there be such as large difference? I asked Lallemand for help. Lallemand strongly recommends that the pitching rate from the manufacturer should be used rather than the pitching rates calculated from books or other sources. Part of the reason for following the producer's recommendations is that they have the technical knowledge of what works best for their yeast. The number of yeast cells and their vitality may vary widely between manufacturers. Another possible reason is that the often recommended pitching rates such as .75 million cells/mL/degree Plato are intended for repitching harvested yeast, which is a common commercial practice (White and Zainasheff, 2010, p. 122). A fresh, healthy culture might need a lower pitching rate compared to the leftover yeast from the bottom of a fermenter.
This calculator is based upon information provided by the most popular yeast producers. Keep in mind that the results are general guidelines. There may be certain strains, such as Lallemand's New England, that might require their own special pitching rate.
Ale yeast recommendations from the yeast producers:
The recommended lager pitching rates are typically double the ale pitching rates, or possibly even higher for high-gravity lager beers.
There are many other complex issues to consider. The dry yeast makers recommend rehydrating the yeast prior to pitching to get the best results. Skipping this step may shock the cells and lead to fewer living cells. A common recommendation for wet yeast is to make a smaller starter of 1 to 2 Liters for a 5 gallon (19 L) batch. The cell growth produced by these starters depends upon the size, wort gravity, agitation of the wort, and stepping procedures. Please refer to the calculators provided by Mr. Malty or Brewer's Friend for more information.
In conclusion, it seems as if the recommended pitching rates for all of the yeast companies seem to run lower than the commonly used pitching rates recommended by some sources. Healthy, fresh yeast can be pitched at a lower rate than the industry standards for repitching the yeast left over from fermentation. The above recommendations are just general guidelines to give an approximate amount of yeast needed. Be sure to review the information provided by the various manufacturers before making your final decision.
Hyde, A. (2018, March/April). Yeast propagation and pitching, BYO, 84-86.
White, C., & Zainasheff, J. (2010). Yeast: The practical guide to beer fermentation.Brewer's Publications, Boulder, Colorado.
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