Brewing reliably delicious beer requires quality ingredients, recipes, and (my personal favorite) operations. Though hops often get the glory in the modern craft brewing scene, it’s important to understand that the fermentation process, driven by the natural life cycle of yeast, is truly at the heart of the beer making process. In the brewhouse, a brewer has many tools to manipulate and construct wort, but once sent to the cellar the yeast take over and do all the heavy lifting of making beer. A well-thought-out yeast management program provides a brewery with a steady supply of healthy yeast, untainted with contaminants, allowing the brewery to operate unhindered as it delivers batch after batch of delightful ales and lagers. This article identifies the top 5 challenges in yeast management and discusses solutions to overcome them.
Problem #1: Improper Record Keeping
Solution: Keeping detailed, accurate records of yeast movement within the brewery cellar is foundational to successful management and so it is critical to record detailed information for every yeast pitch. Key factors to record for each re-pitching are:
- Yeast strain
- Original pitch date or received date
- Cell density
- Brand/batch harvested from
- Brand/batch pitching into
- Tank harvested from
- Tank pitched into
This information along with proper cellar and brewing records will provide powerful tools when troubleshooting problematic beer fermentations, projecting seasonal yeast requirements, as well as ensure that the proper yeast and quantity are pitched accurately.
Problem #2: Poor Performance from In-House Yeast Propagation
Solution: Just as it is for every other process in the brewery, hygienic processing of the propagation steps must be practiced. Take all necessary steps to ensure that each consecutive step-up in culture volume is done without contamination. All smaller volume transfers should be done in a clean room under a hood or next to a lamp. All glassware and media must be sterilized.
While stepping up the volume of the propagation (and thus the total cell count), a good rule of thumb is to step up slowly and never larger than a factor of 10x – this rule allows for approximately 3 doublings of healthy cells and increases the total cell count to approximately 8x the original volume in 24 hrs. For example, if starting with 20 ml, the next step is 200ml, followed by 2L, then 20L and so on until you’ve reached the volume necessary for a fermenter.
Problem #3: Mismanagement of Multiple Yeast Strains
The most difficult part of yeast management for multiple strains is proper scheduling of each strain’s corresponding brand or brands. To minimize yeast costs by maximizing re-pitches, a brewer must carefully plan the brewing schedule. Utilize past records to leave ample time between brews so yeast storage can be minimized, and to ensure that healthy yeast is available for each batch.
Optimally yeast should be pitched within a few days of terminal gravity of the parent beer – this ensures high viability and vitality. Of course, in many situations this is not possible. On occasions where yeast must be stored outside of a fermenter be sure to follow the necessary protocols to maximize the lifespan of the yeast slurry:
1. Store yeast in an airtight sanitized vessel
2. Transfer the slurry hygienically straight from the cone to the storage vessel
3. Ensure that the storage vessel is purged of air and the yeast is stored under CO2
4. Store the yeast cool location, preferably <42F
Cross Contamination of Strains
Care should be taken to not cross contaminate yeast strains. Product lines should undergo a complete CIP/SIP cycle between handling of brands. Take the time necessary to check that all contact surfaces are being cleaned and sanitized, as well including manifolds, valves, and fittings, because even minute amounts of strain contamination will eventually become problematic. This is especially true when the contaminated yeast is serially re-pitched.
Problem #4: Inconsistent Fermentations
Consistent Viability and Vitality in pitches
How many living (viable) cells are pitched into your wort directly is a crucial predictor of a good or poor fermentation. Spending the time to standardize this metric will help greatly in preventing bad fermentations. Use the common methylene blue staining protocol on yeast slurries before pitching to calculate the amount of slurry to pitch. This can be further confirmed by counting the suspended cells within the beer directly after pitching
Viability measures the living cells within a slurry, but more critical is how healthy those cells are. Vitality is the measurement of how healthy yeast cells are. This measurement takes into account energy storage and sound internal metabolic functionality in the cell. A vital cell will immediately begin fabricating the necessary proteins to process the wort and will have no problems replicating. Methods for measuring this property are under development but a solid understanding of this distinction is useful for successful yeast management.
Supplying ample amounts of oxygen in the wort allows yeast cells to grow and replicate effectively. Though some of this oxygen is used for aerobic metabolism, most is brought into the cells’ vacuole and utilized to manufacture unsaturated fatty acids which are necessary for cell reproduction.
The best way to ensure adequate oxygenation is through a dissolved O2 measurement of your wort. A common rule of thumb is:
1 ppm/degree plato when using pure oxygen
8 ppm when utilizing air
Measuring in-line without introducing the wort to the atmosphere is the most accurate way to achieve reassurance. However, hand held meters will suffice. Once an adequate level has been achieved through temperature, fluid flow, and gas flow adjustments, write down these parameters. Standardizing the procedure will ensure that the DO concentration is consistent from batch to batch.
Problem #5: Too Many Generations
Solution: Understand your yeasts’ capability to be serially re-pitched. Yeast populations will undergo epigenetic changes as the slurry is pitched batch-to-batch. The changes that take place will depend on many factors and change from strain to strain. Strain characteristics that may drift include but are not limited to: flocculation capacity, flavor profiles, viability/vitality, and attenuation rates. The make-up and strength of the wort, storage strategies, hop varieties, fermentation temperature, oxygenation, and many other factors affect this change from pitch to pitch.
Again, be sure to keep records of your fermentations and use these as tools to understand how far to push your yeast. By following standard operating procedures (SOPs) throughout your brewing process a standard output can be observed. Use these recorded observations to understand the maximum amount of beer you can produce from your yeast.
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