Originally Posted by EarlyAmateurZymurgist
I maintained several brewing yeast cultures for ten years on slant with two year master stock subculture periods (the only reason why the cultures did not last longer is because I lost interest in the hobby). The cultures retained 100% purity because they were plated before being slanted, and all slant-to-slant subcultures were aseptic transfers. Working with -20C or -30C frozen stocks may be more convenient than slanting, but the cultures are lower quality. Short of -70C or lower storage, slants provide the longest viability period because slanted yeast is healthy yeast with ample sterol and UFA stores.
Like I mentioned, plating/slanting has it use, especially when isolating pure cultures. However, for long-term storage, freezing is superior.
It is fantastic that you have been able to maintain cultures on slants for years. You have posted this finding dozens of times.
From a physiological point of view, freezing with a cryoprotectant preserves cell integrity and reduces oxidation, maintaining healthy yeast. Do you store your slants in the fridge after they grow?
Once the yeast cells have grown through their exponential growth phase, and entered stationary growth, they have accumulated all the unsaturated fatty acids and sterols they will need for future growth. In the fridge, the cells are no longer growing and will not be uptaking lipds. Sterols are involved in cell wall permeability during aerobic growth and fermentation, neither of which are important during long-term storage. In fact, in rich media (which wort is), reserves of unsaturated fatty acids and sterols are not required for growth. In yeast, these molecules are used as building blocks for membrane lipids, not as energy reserves. Do you purge oxygen from your slants during storage? If not, oxidation is much more of a concern than lipid accumulation during long term storage.
Based on past posts, you will likely keep slanting. I will continue freezing my yeast stocks. In my laboratory and homebrewing experience, this practice is less time consuming and results in healthier cultures.