Yeast Rehydration and Cell Viability

Hey guys! Been very busy, but still managed to find a little time to do a little mini-study on something that’s been poking at my curiosity for a while. Namely it’s the question of water vs wort and temperature range when rehydrating dry yeast.
According to easily available data around the internet, rehydration in water is the way to go. However no concrete numbers are ever provided, which makes it difficult to convince “no rehydration believers” that there is any difference. Also you don’t even know if it really makes a difference or not. So I decided to take a look at the issue.
The results seem to agree with the “warm water is the way to go” point of view. Obviously this is not dogmatic and if you disagree or doubt, by all means do your own thing :slight_smile:
Check it out ... hydration/


So your conclusion is that rehydrating at pitching temp (16c/61F) only yields ~20% viability?

Why do you believe that is the case?

I can understand the theory of why wort is less desirable than water. But cold v. warm water is baffling me.

I’m not sure why, but lower temperature kills dry yeast. Actually the only reason why I even looked at the temperature series is because I read online from a guy who works on dry yeast that at ~60F viability drops to ~40%. I think it has something to do with cell contents leaking.
I imagine in reality it’s a little more than what I got due to age of the packet, but it is what it is.
Water hardness also plays a role.