Fermentation
Yeast pitching rate
One pack for 20 litres? The calculation asks for two for an ale at 1.050, and double that for a lager.
Result
Fill in the values and run the calculation, or try the example.
This is the calculation Krausi uses. Create an account to save it in a recipe or a brew.
Create my accountWhy calculate the amount of yeast?
Yeast makes the beer, and how much you use matters as much as which strain. With too few cells, fermentation starts slowly, drags on and leaves off-flavours: solvent, green apple, butter. With far too many, the yeast does not multiply and the beer lacks fruity aromas.
It is the cheapest setting to fix: one more pack solves the problem. You still need to know how many it takes. The answer depends on the volume, the gravity and the type of yeast: a lager, fermented cold, needs twice as many cells as an ale.
How is the pitching rate calculated?
The cells needed are proportional to the volume and to the gravity, expressed in degrees Plato:
cells (billions) = rate × volume (L) × °PlatoThe rate is 0.75 billion cells per litre per degree Plato for an ale, 1.0 above 1.060. For a lager it is 1.5, and 2.0 above 1.060.
For dry yeast, the tool counts 10 billion cells per gram, which is 115 billion per 11.5 g pack, and rounds up to the next pack. For liquid yeast, it starts from 100 billion per pack and takes off 0.7% viability per day of age.
Worked example
Values entered
- Wort volume in litres: 20
- Original gravity as decimal SG: 1.05
- Beer type: Ale
- Yeast form: Dry
Result from the tool
- Original gravity in °P
- 12.39
- Pitching rate applied
- 0.75
- Cells needed, in billions
- 185.78
- Viable cells per pack, in billions
- 115
- Number of packs (rounded up)
- 2
What the tool does not do
- The 10 billion cells per gram is a cautious value: some dry yeasts contain twice that. Check the manufacturer's data sheet.
- The loss of viability of a liquid yeast is a linear approximation.
- The calculation does not account for rehydration or wort oxygenation.
Frequently asked questions
Should I rehydrate dry yeast?
Manufacturers now allow direct pitching. Rehydrating in lukewarm water for 15 minutes is still useful for very strong worts, where the sugar stresses the yeast.
Is a 3-month-old liquid yeast still good?
It is alive, but weakened: at 90 days, the tool estimates its viability at 37%. For 20 L at 1.050, you would need 6 packs. Make a starter with just one instead.
Why more yeast for a lager?
A lager ferments between 9 and 13 °C. At that temperature the yeast multiplies slowly: you need to pitch twice as much for fermentation to start properly.
And with the assistant?
Krausi knows the volume and gravity of your recipe: just ask him how many packs to plan for.
How many packs of dry yeast for my 20 L at 1.050?
For an ale you need 186 billion cells, which is 2 packs of 11.5 g. For a lager it would be 4 packs. I'm noting 2 packs in the recipe.