Lager Yeast and Fermentation
In this blog, we will discuss some of the core elements of lager yeast and fermentation. Although we will only scratch the surface of this subject, a full presentation on the subject can be found by clicking here. Key points in this presentation include yeast pitching, aeration, yeast growth, fermentation, end-of-fermentation protocols/Kräusening, flocculation and yeast harvesting, maturation, and flavor.
First, the amount of yeast added, and its condition is critical. Target pitching 1.5 million cells per degree plato (pitch 18 million cells/ml for a 12-degree plato lager). Pitch yeast that has been recently harvested; yeast that was harvested within the past week and fed, or yeast that has not been stored under fermented beer for excessive time.
Furthermore, alcohol, low pH of dense slurries, elevated temperatures (diacetyl rests), as well as hydrostatic pressure, are all bad for yeast. Temperature, time, and agitation are also detrimental factors to stored yeast health.
Yeast pitching must be spot on. Both underpitching and overpitching carry unwanted results. For example, underpitching yeast results in slow fermentations risk microbiological integrity, and cause increased acetaldehyde, SO2, esters, and increased beer pH. On the other hand, overpitching tends to produce off-yeasty flavors and increased acetaldehyde, pyruvic acid, and acetoin.
For peak lagering success, knockout your wort! In other words, aerate it. Perform aeration in-line between the chiller and fermenter with sterile air (not oxygen!). At 50-53F, wort saturated with air will give 8-10 ppm dissolved oxygen. However, be sure to knockout colder than the fermentation temperature.
However, pay close attention to your aeration. Under aeration will result in slower fermentations, higher acetaldehyde, SO2, lower alcohols, lower yeast growth, lower yeast viability, and lower yeast yield. Conversely, over-aeration results in higher peak cell count, higher peak acetoin, and the higher end of primary acetoin increased esters, lower SO2.
For a complete presentation on lager yeast and fermentation, click here.