lovky,
Dry Yeast - billions of cells per gram:
No one agrees on the number of yeast cells per gram in dry yeast!
This is made more confusing because each yeast strain has different size cells and clumping tendencies.
We put in a reasonable default of 10 billion cells per gram of dry yeast.
Kaiser located a study which reports the following data on dry yeast ranging from 8-18 billion cells per gram:
Yeast B cells/g
Safale K-97 14
Safale S-04 8
Safbrew T-58 18
Safbrew S-33 16
Saflager S-23 10
Saflager S-189 9
Adapted from: Van Den Berg, S., & Van Landschoot, A. (2003). Practical use of dried yeasts in the brewing industry. CEREVISIA, 28(3), 25-30 (Table 1).
Mr.Malty says that dry yeast contains 20 billion cells per gram. Unfortunately we could not find a reference to a study that supports that number.
From the manufacturers:
Fermentis: > 6B cells/gram for US-05 and S-04.
Danstar: > 5B cells/gram for Nottingham yeast.
These numbers sound conservative and do not match with the study referenced above. According to our pitching calculator, with dry yeast, using the mfg's number of 6B cells/g, to hit a pitch rate of 0.75 (M cells / ml / ° P) for a 5 gallon batch @1.050 would require 3x 11g packs!
Link to a researcher claiming 20B, but only has an n of 1.
Most dry yeast packs come in 5g or 11g amounts. With dry yeast, starters are typically not made because dry yeast is relatively cheap - just buy more packs to hit the target pitch rate.
Liquid Yeast Logic / Assumptions:
A pack/vial contains 100 billion cells at the date of manufacture.
Liquid yeast viability drops 21% each month, or 0.7% each day, from the date of manufacture. The assumption is the yeast viability drops in a linear fashion. In 4.75 months or 143 days, this calculator assumes the yeast is 100% dead (100 / 0.7 = ~143).
From the White Labs FAQ 11/2012: What is the shelf life of White Labs Yeast? Quick Answer: 4 Months. Long Answer: .... After 30 days in the vial, the viability of our yeast is 75-85%,...
There is plenty of online debate as to how the decay works in real life (exponential vs linear). Additional research is called for.
Специально для тебя переведу выделенное - если исходить из кол-ва клеток на 11г пакет равного 6млрд\г - получается что, что бы сбродить 21л(5 галлонов) сусла плотностью 1.050 понадобится 3! пакета дрожжей по 11г.
А теперь вопрос. Сколько пакетов по 11г ты используешь для 21л пива?
и заметь обычно пишут >6млрд\г, т.е. как и на пиве пишут "не менее 4.5%" про содержание алкоголя.
ну и спецом сейчас погуглил упаковки того же ферментис. ни на одной упаковке 11.5г не указано кол-во клеток на грамм. только указано, что пакета
достаточно для сбраживания 20-30л сусла