Many commercial breweries order smaller quantities of yeast to propagate prior to inoculating a larger volume of wort. Propagations can be a cost effective yeast management method for brewers who want to employ multiple yeast strains or are brewing too infrequently to re-pitch harvested yeast. Propagations also allow more frequent ordering without the cost of direct pitching.
A basic rule to follow in determining a propagation schedule is not to exceed a 10-fold increase in volume.
Timing for stepping up the yeast depends on reaching peak cell density at each step. This will be dependant on temperature and the initial pitch rate. Always confirm 50-75% gravity drop prior to increasing the volume. Perform all propagations at 68 °F (20 °C). Fermentation temperature can be adjusted on the last step. When performing a typical 1-Step-10-Fold propagation, peak cell density should be achieved in approximately 48 hours.
A 1-Step-10-Fold propagation is the most common type of propagation used by brewers. This is a single step propagation which involves inoculating a small volume of wort, allowing it to attenuate 50-75%, and then adding a 10-fold volume of oxygenated wort on top.
Determine the volume of propagation wort by dividing the final desired fermentation volume by 10. Next subtract this volume from the final desired fermentation volume to determine the amount of wort needed for the final fermentation.
Example: A 20 Bbl (23 hL) final fermentation volume will require a 2 Bbl (2.3 hL) propagation. Following gravity drop, an addition of 18 Bbl (21 hL) of wort will be required for this fermentation.
The following are typical pitch rates for a 1-Step-10-Fold propagation:
- Ales: 1 liter per Barrel or Hectoliter
- Wheats: 1 liter per Barrel or Hectoliter
- Lagers: 2 liters per Barrel or Hectoliter
- High Gravity: 2 liters per Barrel or Hectoliter
Propagation Example (1-Step-10-Fold):
A 20 Barrel brewery wants to propagate yeast for a 1.060 gravity beer.
- The brewery would order 2 liters of yeast and inoculate 2 barrel of well oxygenated wort at 70 °F.
- The propagation would be allowed to ferment for 48 hours or until 50-75% gravity drop.
- Following gravity drop, 18 Bbl of wort would be run in on top of it.;
The initial cell count in this example would be around 10-12 million cells per mL. If the yeast is allowed to ferment for 48 hours, the cell count would increase enough to supply 5-6 million cells per milliliter when increased to a total of 20 barrels.
Many times a 1-Step-10-Fold propagation does not fit with the brewers specific needs. Wyeast laboratories now offers the Wyeast Cell Growth and Pitch Rate Calculator™ to allow brewers to determine their own custom propagation schemes.
Please see Wyeast Cell Growth and Pitch Rate Calculator™.