Freeze-drying yeast
TroubleShooting
Don Foster asks,
I read an article on saving yeast and started to think about long-term storage. I have a small freeze dryer from Harvest Right that I use for storing food for camping and hiking. Those foods rehydrate pretty well. What are your thoughts on actually freeze-drying, not just freezing, the yeast for use later on? Do you think it will work or has anyone tried this at home?
Freeze-drying, or lyophilization, has been used for drying bacteria and yeast for nearly 100 years. The process begins by freezing, followed by subjecting the sample to a vacuum. The low pressure results in sublimation, where solid water, aka ice, directly changes phases into water vapor without moving through the aqueous phase; totally sublime. Although freeze-drying works well for food products, it is a stressful process for living cells and tissues. One of the earliest references investigating the application of freeze-drying to brewing yeast is the work of Wickerham and Andreasen of the Wallerstein Laboratory (NYC) in 1942. While brewing yeast can be freeze-dried, two complications are relatively high loss in viability and a change in the population of cells.
A study by Jean Wynants, titled “Preservation of Yeast Cultures by Lyophilization,” published in 1962 in the Journal of the Institute of Brewing showed a population increase in respiratory deficient mutant cells, known as petite mutant, after freeze-drying. Wynants concluded that the freeze-drying process led to low cell survival rate selected for petite mutants, thereby skewing the population of cells after rehydration. He also concluded that freeze-drying requires a selection step following rehydration, then propagation using the standard method of the time where a colony is transferred into a small volume of wort to begin a series of propagation steps. This method is still the norm today.
Freeze-drying is used to preserve yeast and does indeed allow for long-term storage of cells. Many yeast labs around the world send freeze-dried cultures by mail to labs and commercial users (breweries, wineries, bakeries, etc.) because of its convenience. One of the keys to the method is using a lyoprotectant agent to add protection to the culture before freeze-drying. Examples of lyoprotectants include blood serum and disaccharide solutions made from sucrose or trehalose.
You have a freeze dryer and are interested in trying it with yeast. My suggestion is to read more about how this technology is used to dry living cultures and give it a try. The worst thing that can happen is that you end up with dry, dead yeast!
