Hardly the most complex of how to's this one It does surprise me the number of methods that people use, and most of them are not correct . . . . for brewing yeast! Bread yeasts are a completely different animal . . . actually they are not . . . and the requirements are different.

Firstly you need to use the correct amount of distilled water Yes that is correct distilled water, not wort or a sugar solution but distilled water . . . No not even tap water . . . distilled water, or certainly water with a low mineral content. The reason for this is simple, when you add a dehydrated yeast cell into a solution it rapidly absorbs liquid, but the yeast membrane is not selective at this stage and allows 'everything' and 'anything' across the membrane, including all those sugars and minerals. This can cause extreme osmotic stress to the poor yeast cell as it tries to wake up, and it will either end up poorly or could even explode and die, not a good result really, so just distilled or low mineral content water.

Secondly the right amount of liquid should be used . . . Fermentis suggest using 10 times the weight of water as yeast, so an 11g sachet of yeast needs 110g of water (which is as near as dammit 110ml), 100g of yeast needs 1000ml

Thirdly, the water, after boiling to ensure sterilisation, needs to be at the correct temperature, and this varies for variety to variety. Nottingham for example needs to be at 36C . . . Fermentis Saflager W34/70 needs 21-25C, . . . SO4 needs 25-29C. Lallemand report a 20% loss in viability compared with rehydrating at 30C instead of 36C . . . and if you are close the limit for under pitching this could be an important factor. DO NOT guess the temperature! Use a thermometer! This is one of the easiest things to do, and guessing wrong will almost certainly kill your yeast.

Fourthly, Sprinkle the yeast onto the surface of the cooled water and stir gently to mix it in . . . I know it just says sprinkle it on and leave it . . . but you need to stir it to mix it in, (I actually use my stir plate while pouring the yeast into the sterile conical flask), and then leave it to stand (covered) to rehydrate usually 15-30 minutes depending on variety, (Lallemand say 15, Fermentis 30).

Fifthly, as you are filling the FV with cooled wort, give the yeast another stir, and pour it into the Fermenter.

Result, Happy yeast ready to get cracking to turn your wort into luscious beer

Great info Aleman

I like humourous factual posts

Great post, rehydrating yeast is a very mystical subject. However, (to put the pigeons amongst the cat) is there any reason why I should follow this regime when just chucking a packet into the wort works?

Pah! A load of old poppycock (That's a joke befoe anyone gets on their high horse)

Great post Aleman.

I don't get the distilled water bit. I understand your reasoning but many just pitch into the wort in the FV, which is water with a load more bits and bobs. Is wort better to pitch into than straight water?

Lallemand and Danstar both say that it is best practice to rehydrate in water rather than sprinkle on the wort, this results in the highest viability of the yeast . . . you can be looking at a 20-25% smaller viable yeast population if you pitch into wort rather than rehydrating properly . . does it make a difference? many brewers 'get away with it' but once you start looking at high gravity worts or larger batch sizes . . . it starts to become important . . . we pitched 2 BBL of 1.100 wort with 500g of Nottingham yeast and had it ferment out to 10.6% in 10 days . . . but we did rehydrate first.

AS I said if you are happy sprinkling then do so . . . but if you are going to rehydrate your yeast this is the way to do it properly . . . not in wort/honey/sugar solution or any other complex mix . . . use distilled/low mineral content water.

Is deionised water ok? eg the stuff you top your car battery or coolant up with?

Yep . . . Or RO . . . I'll be truthful I use tap water . . . . but there is pretty much bugger all in my tap water.

I'll try and remember to change the main how to to include deionised and RO as well.

so is the yeast here used to re hydrate different to dry yeast if so where do i get this yeast or how can i tell difference ? sorry if im being thick

I'll concede that it might be best to use distilled water to re-hydrate your yeast, but I dont see how it could possibly be due the the reasons given above. The osmotic shock of distilled water is going to be far greater than that of water with a high mineral content.

I agree that sugar or hopped wort is not a good idea because thats going to be toxic to yeast with no traffic control... but cant for the life of me see whats worng with tap water, provided its decholrinated.....

The yeast membrane is totally unselective in what it allows through during the first seconds of rehydration. . . . While I concede that the difference between Distilled/deionised/RO water and high mineral content tap water is probably minimal . . . experimental evidence shows that it is best practice to rehydrate yeast in Distilled/deionised/RO/ low mineral content water . . . . and this can be a difference of 10-15% viability between the two depending on the strain.

I agree. If osmotic shock is a factor that can cause yeast cells to "explode and die" then that is an excellent reason not to use distilled water.

@Aleman - what is your source?