Really interested to know if anyone has more info or experience of using old liquid yeast packs or old stored yeast slurry?
Out of intrigue I'm having a go at propagating from a 100 Billion (estimated!?) overbuild yeast slurry that has been sitting in the fridge since February 2019!?
For the experiment I've gone with an assumed 25 million remaining cell count for the 36 month old slurry using Homebrew Dad's model "running" total - you lose 20% in one month, 20% of the remaining balance the next month, and so on.
Step 1 - 100 Fold - 0.016 litres of 1.040 wort with 1% yeast nutrient - 2 million/ml Inoculation Rate - 2-3 Days on stirplate = 2.5 Billion Cells
Step 2 - 10 Fold - 0.16 litres of 1.040 wort with 1% yeast nutrient - 15 million/ml Inoculation Rate - 2 Days on stirplate = 25 Billion Cells
Step 2 - 10 Fold - 1.6 litres of 1.040 wort with 1% yeast nutrient - 27 million/ml Inoculation Rate - 2 Days on stirplate = 250 Billion Cells
All steps calculated using yeastcalculator.com with K. Troester stirplate method.
Definitely something happening already with Step 1 after 20 hours!?What are folks thoughts?