Best Practices - Yeast Propagation
How do I propagate yeast for my brewery?
First of all, note that it takes years to understand the ins and outs of keeping every single yeast strain happy - this is why yeast labs such as Escarpment Labs exist! However, we do have some general suggestions and pointers to help with yeast propagation. Read on below!
What should I feed yeast in propagation? Is malt extract OK?
In general, beer yeast needs malt sugars, complex nitrogen, and pH buffers for optimal propagation. For propagation, we suggest wort between 10-15ºP with at least 200ppm of free amino nitrogen. It can also be helpful to supplement the propagation with added nutrient such as Yeast Lightning.
While malt extracts can work OK, they are often deficient in some useful nutrients. If you are using malt extract, we recommend adding Yeast Lightning to your propagation wort for optimal results.
How much Yeast Lightning should I add to my propagation?
We suggest using Yeast Lightning at 20-40 g/100L. This is higher than the rate we recommend for fermentation (4 g/100L). This is because propagating yeast aerobically will cause it to use a greater amount of nutrients in the wort.
Many breweries propagate yeast in a 1 hL (or 1bbl) vessel. We recommend one 28g (1 oz) pack of Yeast Lightning per hL or bbl of propagation wort.
How should I aerate the propagation?
We recommend aerating your propagation continuously using sterile filtered compressed air. Using pure oxygen at the start only will result in a more standard fermentation process. Using pure oxygen continuously tends to be wasteful/costly.
How much yeast will I get in my propagation?
For a wort-based propagation, expect to yield about 100-200 million cells / mL in your propagation. This means that to yield enough yeast for a 20 hL batch, you may need up to a 5 hL propagator for optimal yeast pitching (depending on yeast strain).
Some yeasts (e.g. Saisons) grow to higher cell density than others. English Ale and Lager strains tend to produce the lowest cell density.
What temperature should I propagate yeast at?
The recommended propagation temperature for most yeasts is between 20-30ºC. You can propagate hotter than you ferment without adverse effects. We recommend the lower end of this range for lager strains and the higher end of this range for kveik, with most other yeasts in the middle. You can propagate lager yeast above 20ºC without issues at lager fermentation temperature.
How much yeast should I use as a seed culture for brewery propagation?
We recommend purchasing an Escarpment Labs liquid pitch sized for your propagator. So if your propagator is 2 hL, you would purchase a 2 hL pitch from Escarpment Labs and pitch this into your propagator to grow up.
What are the risks of propagating in house?
If you are thinking about a propagation program for your brewery, we urge you to consider the financial impact of even one bad propagation ruining one tank of beer in the course of a year, versus the cost of buying full-size yeast pitches from a reputable supplier.
Your annual yeast costs may be lower than the opportunity cost of losing one batch of beer or having slow/stalled/stuck ferments due to errors in propagation.
It's important to think through all the risks and all the possible scenarios where things can go wrong in propagation before committing to a propagation program. Also, consider the labour cost of operating a propagation program.
Yeast propagation is a complicated process to get right every single time. Propagation needs to be taken seriously to ensure repeatable and high-quality beer. We strongly encourage breweries that are propagating microbes in-house first to implement an in-house lab and perform quality control analysis on the propagations.
How do I ensure propagated yeast is pure?
We suggest plating onto WLN, LCSM, and MRS agar for yeast propagations to check for cross-contamination, diastaticus, and spoilage bacteria. Cross-contamination by other yeasts can result in off flavours or excessive attenuation. Cross-contamination by bacteria can result in butyric (vomit), acetic (vinegar), acidic (lactic acid),or sulfury (eggy) off-flavours. We recommend a dosing rate of no less than 5% inoculum to propagation volume, e.g. 100 mL into 2 L, 2 L into 40L, etc.
Propagation consulting
Escarpment Labs is able to work with your brewery on a consultancy basis if you are considering in-house propagation but need some advice from the experts. Contact us for more information.