I re-hydrated my US-05 at 40C ( 105F ) going by this video https://www.youtube.com/watch?v=SL92Bd4kfbQ. However afterwards I read the on the Fermentis site that it should have been at 27C (+/-3). Apparently it's different depending on the yeast and I should have gone by Fermentis' instructions but would I have done any harm.

1 Answer 1


It's close, but I think you'll be OK. The commonly cited temp to kill yeast is about 114F. That's a generalization, but hopefully the yeast will survive. FWIW, despite manufacturer's recommendations, I find no difference between rehydrating and not rehydrating. A very experienced friend who runs a homebrew shop advises his customers not to rehydrate due to situations like yours. This experiment adds data to the point that it doesn't matter....http://brulosophy.com/2014/09/15/sprinkled-vs-rehydrated-dry-yeast-exbeeriment-results/

  • thanks for your vote of confidence. That video is very strange - the're actually using us-04 in the video which is supposed to be re-hydrated at 27 too. I was re-hydrating because it was a fairly high gravity beer. I heard that pitching dry ends up killing a higher percentage of cells and I only had one packet. If I had checked the fermentis site I probably wouldn't have had a problem. Wont happen the next time LOL Oct 27, 2016 at 16:55
  • FWIW, I have often pitched a single pack of US05 unrehydrated in to 1.075 wort and had no problems at all.
    – Denny Conn
    Oct 28, 2016 at 15:41
  • I've seen people report similar experiences; and other people say you're better off re-hydrate - it's funny with homebrewing talk on the web - everybody has such different experiences. I was reading a thread on us05 and half the people on the thread swore by it and the other half swore they'd never use it again. LOL. In the end with re-hydration I sort of thought it would be safer to re-hydrate - and I suppose I had little to loose if I had gone with manufactures instructions but that article suggests its a waste of time though - btw fermentis says wort needs to be above 20/68 for dry pitching Oct 28, 2016 at 18:49
  • As often happens, experience disagrees with "book learning". I have often pitched unrehydrated US05 as low as 58F and had absolutely no problems. Don't believe everything your read-even from me-try things that make sense and see what happens.
    – Denny Conn
    Oct 29, 2016 at 16:32

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