this is what i use to rehydrate. it's worked great for the last five or six batches, so i figured i would post how i do it.
rehydration allows water to pass through the cell walls of the yeast and bring them back to life... something that the cells can't easily do in wort. john plamer recommends it... jamil zaniasheff recommends it... fermentis has a how to on their website... danstar tells you how to rehydrate as well. it's imperative... otherwise you lose about 60% of the cells when you just sprinkle directly onto the wort.
i have a 1 liter pyrex erlynmeyer flask, my brewmometer, a square of aluminum foil, and the packet of dry yeast... that's pretty much all you need to do it.
note: you can use a pyrex measuing cup in place of the flask. just have foil large enough to completely cover the cup. and, anything "pyrex" can be put directly on the heat, and straight into a water bath without shattering.
i start the process once my wort has cooled to 100° F... it usually takes another half hour, or so, for the wort to cool to pitching temps, which is just about how long the rehydration process takes. you want to time it right so you don't let the rehydrated yeast sit around... finish the process and pitch the slurry as soon as it's done.
there is one cup of warm tap water in the flask.
put the flask on the heat, and bring it to a boil.
let it boil for a minute or two... just to sterilize the water (this is also how you make sterile water... so if you see anything that calls for "sterile water", it mean water that has been boiled and cooled).
take it off the heat, put on the aluminum foil square to cover the mouth of the flask, and insert the brewmometer. i have an ove glove that i use to move the flask around... oven mitt, towel, etc... be careful, of course.
put the flask in a water bath so it can cool down to 100° F.
once it's cooled to 100° F, you're ready to sprinkle in the yeast. this recipe i used US-05 in an 11.5g packet, but this process will work for Mr Beer yeast packets, as well. make sure you spray the packet and the scissors with sanitizer... i keep a bottle of star san around just for stuff like this.
you'll see the yeast floating on top. DON'T STIR! just let it sit. 15 minutes. start a timer... clean up from your brew day.
once the 15 mins is up, i swirl the flask to mix the yeast into a cream/slurry and resuspend everything.
it'll look like this...
and you're ready to pitch. just pour the whole slurry into the fermenter. any dilution effect to the wort will be compensated by the alcohol produced during carbonation in the bottle... or i like to think it is.
it's super easy, and when i rehydrate my dry yeast, the beer has started fermenting within 4-6 hours. when i've only sprinkled dry yeast on, it's taken 12-24 hrs for fermentation to kick off... not good.
give it a try... i think you'll be pleasantly surprised at how easy it is and how much of a difference it'll make.
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