Re-hydrating dry yeast

[Ian83]

Is it really necessary to do this step before pitching or is it ok to just lash it straight in

[beerfly]

for your standard < 6% beers it would not make much difference, if you are doing a stronger one i would.
generally i just sprinkle on top and let it slowly soak in.

[Tom]

It's ok, yes. You can rehydrate, but I haven't found a noticeable difference in lag times myself. Only some dry yeast manufacturers recommend it anyway. I think Danstar don't do (Notty etc) and Fermentis (S04 etc) do... from memory.

http://www.fermentis.com/brewing/homebrewing/product-range/ for all the fermentis spec. sheets.

I rarely make a 6%+  beer, but I suspect Beerfly is right there.
Edit: correction
http://www.homebrewit.com/media/pdf/Nottingham_facts.pdf

[Ian83]

Happy days. Thanks a mill. The American beer forums went into far too much detail

[biertourist]

Is it really necessary to do this step before pitching or is it ok to just lash it straight in

Depends if you want to be a mass murder or not..   
Roughly 1/2 of your yeast cells will die if you directly pitch; dried yeast cells cannot regulate their cell membranes until they're rehydrated and they'll let way too much stuff into the cells and then die / get shocked.


Having said that if you want a bit more fermentation by products for flavor (simulating a lower pitch rate) you can directly pitch; if you're looking for a cleaner, more neutral fermentation, rehydrate it first so you don't get as much cell growth and therefore less early fermentation by-product derived flavors.


Adam

[HomeBrewWest]

Page 5 of this may be of interest:
http://cdn.shopify.com/s/files/1/0195/8620/files/MJ_Craft_Series__A5_Yeast_Booklet.pdf?1935

Presumably these pointers apply to most dried yeasts. Summary:
- although MJ yeasts do not require pre-hydration, cleaner and more professional results may be produced if rehydrated before use,
- rehydrated lager yeasts is done at a lower temperature,
- more important for ales of original  gravity over 1.050, and
- more important for lagers fermented at 14°C or lower.