'warm' is probably not a good description though.
make the water about 80-85degrees F. 'warm' water is gonna have to be 100F or above or the body will tell you its cool (since your finger is about 98 degrees).
main reason to rehydrate is really high gravity wort makes it harder for the yeast to rehydrate, but water is no problem.
the ideal thing to do is boil some water, then cover it and let it cool back down to 85F, then stir in the yeast, wait 15 minutes, and then pitch that into the fermenter with the wort, and give it a really good stir/shake (to aerate the wort).
Primary: English Mild
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