In this era of supply chain issues and manufacturers’ guarantees failing, it is more crucial than ever for brewers to understand how to become self-sufficient. A significant part of this self-sufficiency involves maintaining the viability of beer yeast.
Yeast and Brewers
The relationship between brewers and yeast used to be clearly defined.
Yeast, as a simple single-celled organism, has one job. It exists in the atmosphere, on surfaces, and even in our bodies, seeking sugar. When it detects sugar, it consumes it, converting it into alcohol and carbon dioxide through the process of fermentation.
The brewer’s role is also uncomplicated. For thousands of years, they have harvested grain, malted it, cracked it open, boiled and steeped it, and then waited. The native yeast present in the environment happily activates, sensing the sugar in the wort, consuming it, and transforming grain water into ale.
What Yeast Needs
In the past, it was unnecessary to keep yeast alive. Yeast thrived in the wild, and brewers would utilize it when they were ready to ferment. Yeast always arrived on time. However, nowadays, we desire more control over the process, so we harvest our own yeast.
Yeast requires a constant supply of food. Remember, it continually seeks sugar. In natural conditions, when it cannot find sugar, it does not die; it becomes dormant.
To harvest our own yeast, we can attract wild yeast from the region by placing a jar of dried fruit covered with filtered water under a nearby tree for a few days, allowing the yeast to ferment. We can also harvest yeast from our favorite beer by pouring the sediment from three or four bottles into a separate container, rinsing and collecting the yeast. Alternatively, we can purchase yeast from a reliable manufacturer and initiate the growth process from there.
But how do we keep beer yeast alive?
Preserving Beer Yeast
Preserving something that naturally thrives in the wild within a controlled environment is not always easy. Yeast needs a constant sugar source or ideal conditions to remain dormant. The three most common methods brewers use to keep their yeast alive may not be effective long-term.
Slants, mineral oil, and silica gel are suitable for storing yeast for a few months, but they are labor-intensive, prone to contamination, and lose viability if not used quickly enough.
Slants require scratching a bit of yeast onto an agar plate, keeping it sterile, and storing it in the refrigerator. Viability needs to be checked periodically, and the yeast should be transferred to a fresh plate every few months, all of which carries a contamination risk.
With mineral oil, a similar process to slants is followed, but the slants are covered with mineral oil to slow down cell division, increasing yeast longevity. This method is messy, and the cultures must be refrigerated, occupying significant space and presenting contamination risks.
Lastly, with silica gel, yeast cells are desiccated, dried out, and stored in a non-frost-free freezer, potentially extending their lifespan up to a year. However, this method requires extensive equipment and effort.
Ultimately, distilled water appears to be the best method for preserving beer yeast.
To store yeast, you will need dram vials, a heat-resistant rack, a pressure cooker, distilled water, agar plates or slants, an inoculating loop, a flame source, and disinfectant. Most of these materials are likely already available if you have been involved in yeast storage, and those that are not can be easily found at brewing supply stores. This process allows you to keep your yeast alive for years.
Ensure all equipment is sterile by using disinfectant and flaming lids and rims before use.
Use the inoculation loop to transfer a small amount of yeast onto an agar plate or slant.
Fill the dram vial about one-third full with distilled water, lightly place the lid on, and sterilize the vial in a pressure cooker at 15 psi for 20 minutes.
Transfer the agar plate or slant to the vial, screw the lid on tightly, and shake the vial to break up yeast clumps.
Place the vial in the rack and store at room temperature, away from sunlight, for years.
When ready to use the yeast, simply reculture it by adding a small amount to a small volume of wort, such as 1 liter. After a day, add this mixture to 5 liters as the yeast will multiply with each pitch. The entire reculturing process takes a few days, so plan accordingly for your next batch.