Last month I began an experiment looking at the effectiveness of drying kveik (Norwegian farmhouse yeasts). The short version is that I dried the yeast slurry from an IPA fermented with the Voss kveik strain. I didn’t use anything fancy for this – in fact, I used a cheap food dehydrator that uses a fan and an unregulated heater to dry the food.
Despite the cheap dehydrator, the dried kveik had over 99% viability 24 hours following drying. Today, 1 month after drying, I’m repeating the viability assay to see how the yeast has held up. To be clear, the dried kveik has been placed in a plastic zipper bag with most of the air pushed out. This bag has been stored in a freezer at -20C (-4F). But nothing else has been done to aid the yeasts’ survival.
Drying Kveik – Viability at 1 Month
As with last time, I assessed viability with trypan blue. This is a dye which is excluded from living cells, but which stains the interior of dead cells a deep blue.
To start, a small amount of dried kveik is rehydrated in 1 ml of sterile water. I allow the kveik to dehydrate for 15 minutes, then stain with trypan blue. The sample is then immediately loaded into a hemocytometer and imaged on my microscope.
While not obvious in the image to the left (click image for full size), there are some cells that stain a faint blue throughout. After counting 8 fields, I found that the yeast had 94% viability. This is down ~6% in a month. If that rate holds true, kveik stored in this manner should be usable (>50% viability) for ~8 months. Viable yeast should be recoverable for several years.
Join me again this time next month, when we check the kveik’s 2-month viability!