If I rehydrate my yeast, how long can it sit in the water until I pitch it?

I'm going to start brewing in about three hours, and I'm wondering when I should boil some water for rehydrating my yeast? Seems like it might take awhile for the water to get down to 90 degrees after its been boiled. If I boil now, can the yeast sit in the water for a couple hours?

yep

+1

Pretty sure they'll be just fine.

I know it is not exactly the same but I use to make sourdough bread. Captured some wild yeast from the environment, built a starter that was used as needed, fed and kept in the fridge for years. Even at fridge temps the starter would grow and often times I made my bread dough at night, put it into the fridge, it would "grow" some, pull it out the next day and let warm back up to room temp. I'd then make the the loaf and let rise till ready for the oven... hours usually

The cold temps didn't hurt the yeast at all, actually it brought out character

If brewers yeast is half as resilient as bakers yeast.. a few hours in water will not harm it.

In general boil it and you can chill it very quickly in a small pan with ice and cold water, i put it in a pyrex measuring cup covered with plastic wrap. If you want it cooled really quick stir the ice bath pan. I normally boil the water towards the end of the main boil cool it and while my wort is cooling its then cooled to yeast tempat i then hydrate my yeast when the main wort starts to near room temp which takes me 30 min,so in general a good guideline is to hydrate it for 15 min-30 min. After that your yeast are looking for something to do or eat like being in wort. Its easy enough to do while your wort cools starting to boil and cool the water at the end of the wort boil. Its unnessasary to do it 3 hrs before hand.But it will still make beer.I would think being warm and nothing to do for 3 hrs the yeast would get stressed-thats just a guess.Dont know if its considered good brewing practice as its suggested to pitch it within 15-30 min.
I think the idea is to not let the hydrated yeast cool to room temp that much before pitching, its suggested to keep it at the hydration temp until you pitch it into your wort.

I don't have direct experience, but I've used at least one yeast (I think it was 71B-1122) that instructed you not to leave it longer than something like 45 minutes after rehydration. I doubt it's going to ruin anything, but I'm of the opinion one ought to follow the manufacturer's instructions as a general rule.

Why the hurry? I'd wait until you're just about ready to pitch, it isn't going to take long to cool the boiled water to rehydration temperatures, and it's not going to hurt the wort to wait half an hour while you rehydrate.

jonmohno said:

I think the idea is to not let the hydrated yeast cool to room temp that much before pitching, its suggested to keep it at the hydration temp until you pitch it into your wort.

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So it is OK to pitch the 90 deg. yeast into the 70 deg. wort? I assumed that this may shock the yeast a bit.

breweRN said:

So it is OK to pitch the 90 deg. yeast into the 70 deg. wort? I assumed that this may shock the yeast a bit.

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Well its recommended to add some of the wort, i wait til i hit 75 then pour some in to the hydrated yeast then further coool the wort to 65-70.By the time i poured strained and aerated my wort i pitch the yeast. It wouldnt hurt for it to cool about 5 deg or so naturally but is not recommended to let the hydrated yeast to cool naturally by itself. A gradual introduction into the wort is ideal. If doing that seems a pita,dont worry about it but generally 20 deg diff can shock it some.Im not shure if you should just coool your wort to like 75 pitch your yeast and allow that to cool to room temp which could be 67-70.Im shure that would be fine im still trying to figure out the best process.Alot of people seem to like to cool their wort to 60 and how they hydrate i dont know.

I'm reality you don't even have to hydrate dry yeast. BYO tested this and there is no difference.

+1 if you dont wanna, i made plenty of good dry pitched beers with no complaints. I always try to troubleshoot making better beers-which is so variable it could be anything from water -yeast pitch-ingredients and plenty of others.