Brewing beer that is reliable and delicious requires high-quality raw materials, recipes, and operations. While hops have been successful in modern craft beer, understanding the fermentation process driven by the natural life cycle of yeast is essential to brewing beer. In a craft brewery, the brewer uses various tools to manipulate and produce wort. However, once the wort is sent to the fermentation tank, the yeast takes over all the heavy work of brewing beer. A well-managed yeast plan provides the brewery with stable and healthy yeast, ensuring that the beer brewed is not hindered by contaminants. In this article, we will explain the five major challenges in yeast management and discuss strategies to overcome them.
Five Challenges of Yeast Management
(1) Improper Record-Keeping
Maintaining detailed and accurate records of yeast movement in the fermentation tank is crucial for yeast management. It is important to record detailed information about each stage of yeast, including:
- Yeast strain
- Original pitch date or received date
- Cell density
- Brand/batch harvested from
- Brand/batch pitching into
- Tank harvested from
- Tank pitched into
These records, along with proper fermentation records, help troubleshoot problematic beer fermentations. Additionally, they can be used to predict seasonal yeast demand and ensure accurate yeast pitching.
(2) Poor Yeast Reproduction Performance
In the fermentation process, yeast propagation steps must be sanitized, similar to other processes in craft beer brewing. Necessary disinfection steps should be taken during fermentation to prevent contamination during each successive increase in culture volume. When transferring wort to the fermentation tank, it must be done in a clean and hygienic environment with sterilized pipes and tanks.
During the yeast propagation stage, it is recommended to allow yeast to increase slowly, with the yeast cells reaching about 8 times their original volume within 24 hours. This helps maintain healthy yeast cells.
(3) Poor Management of Multiple Yeast Strains
The proper distribution of multiple yeast strains involves arranging the corresponding brand for each strain. To reduce yeast costs by maximizing re-pitching, brewers must carefully plan the brewing schedule. Sufficient time should be allowed between brews to reduce yeast storage and ensure that each batch of beer has healthy yeast.
The best practice is to pitch the yeast within a few days after the parent beer reaches its final gravity to ensure high viability and vitality. If yeast needs to be stored outside the fermentation tank, specific conditions must be followed to maximize the yeast slurry’s shelf life:
- Store the yeast in a sealed sterile container
- Hygienically transfer the yeast slurry from the cone of the fermentation tank to the storage container
- Ensure there is no air in the storage container and store the yeast in CO2
- Store the yeast in a cool place, preferably at a temperature below 42°F (5.5°C)
Cross-Contamination of Yeast Strains
Brewers should take precautions to avoid cross-contamination of yeast strains. After brewing a batch of beer, the equipment should be cleaned using the CIP system to remove any remaining yeast in the tank. Brewers need to thoroughly clean and disinfect all contact surfaces, including pipes, valves, and fittings. Even a small amount of strain pollution can eventually affect the beer’s flavor. Contaminated yeast will also impact the taste of subsequent batches after re-pitching.
(4) Inconsistent Fermentations
Consistent Viability and Vitality in Pitches
The amount of live yeast directly added to the wort is a key factor in determining the fermentation process. Standardizing this indicator helps prevent incomplete fermentation. The common methylene blue staining protocol can be used to calculate the amount of yeast slurry before pitching. Additionally, brewers can directly assess the vitality of yeast cells by examining the suspension cells in the beer after pitching.
Measuring the number of living cells in the yeast slurry is important, but equally important is the health of these cells. Yeast vitality indicates the yeast cells’ health, considering their storage capacity and internal metabolic function. Healthy yeast cells should immediately start producing the necessary proteins to process the wort and replicate without issues. Methods to measure this characteristic are being developed and are crucial to successful yeast management.
Providing sufficient oxygen in the wort allows yeast cells to grow and replicate efficiently. While some oxygen is used for aerobic metabolism, the majority is used to produce unsaturated fatty acids necessary for cell reproduction.
Measuring the dissolved oxygen of the wort is the best way to ensure adequate oxygenation. As a general guideline:
- 1 ppm/degree Plato when using pure oxygen
- 8 ppm when utilizing air
Online measurement, without exposing the wort to the atmosphere, is the most accurate method. Maintaining standardized processes for temperature, fluid flow, and gas flow ensures consistent dissolved oxygen concentrations in each batch.
(5) Too Many Generations
Brewers must understand the limitations of yeast strains in terms of continuous reproduction. With each generation, yeast populations undergo genetic changes, which depend on various factors such as the composition and concentration of wort, storage methods, hop varieties, and fermentation temperature.
Keeping fermentation records and using them as a tool to understand yeast capabilities are crucial for brewing businesses. Consistently following standard operating procedures throughout the brewing process ensures a consistent beer output. Use these records and observations to determine the number of batches that can be produced from the yeast.