Rehydrating Dry Yeast

Well, since this is, in part, a “homebrew” blog, I figured it was about time I put up a post about homebrewing ūüôā

One of the most important aspects of tasty and successful homebrewing is fermentation. If you get fermentation under control, and hae good, consistent, clean-tasting results, you’re on your way to perfecting your homebrew. And, no, you don’t need to spend $8 per batch for one smack pack or vial of liquid yeast. Dry yeast is fine for most beers. Sure, if I was brewing a hefeweizen, I would go out and get a proper liquid strain, but if I’m brewing an English extra special bitter (ESB), or an American pale ale (APA), a Belgian wit, a red ale, or a stout (note: you can apply a dry yeast to most any style of beer… this is just a list of examples), I’m only spending $3 or $4 on a packet of dry yeast instead of going out to get a “specialized” strain of liquid yeast for twice the price.

And, to get the most out of the dry yeast, you’ll need to rehydrate the cells. Yeast are single-celled organisms, and dry yeast is nothing more than dehydrated yeast cells… they need to brought back to life, like sea monkeys. Proper rehydration allows water to pass across the membrane of the yeast cell walls, which allows the yeast to come out of suspended animation, and get put back to life to get to work fermenting your wort into beer. If you just “sprinkle” the dry yeast onto the wort, the yeast will not be able to draw water across their cell walls properly and will not rehydrate and die. In fact, it’s said you lose 60% of the cells when you just sprinkle the dry yeast on top of the wort. So, if pitch an 11.5 gram packet of dry yeast onto the wort, only 4.6 grams of yeast will survive and actually¬†ferment¬†the wort… the other 6.9 grams are D-E-D, dead… and you’ve just underpitched your beer. And no one wants the results of an underpitched beer… poor attenuation, off flavors, stressed out yeast… just not good beer.

So here’s how I do it:

Get the things you’ll need… I have a 1 liter “Pyrex” erlynmeyer flask, my brewing thermometer (brewmometer), a square of aluminum foil big enough to cover the mouth of the flask, scissors, and the 11.5 gram 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 a square of foil large enough to completely cover the cup. and, any labware labeled “Pyrex” (borosilicate) can be put directly on the heat, and straight into a water bath without shattering. Pyrex measuring cups should be microwaved until the water comes to a boil… probably 2 or 3 minutes on high.

I start the process once my wort has cooled to 100¬į 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 of rehydrating the dry yeast 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 the water to a rolling ¬†boil. You can optionally use the microwave to bring the water to a boil… 4 or 5 minutes on high should be good… just be¬†leery¬†of flash boil overs when you take it out.

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).

CAREFULLY take it off the heat and put on the aluminum foil square to cover the mouth of the flask.¬†I have an Ove Glove that I use to move the flask around and put on the foil… oven mitt, towel, etc… be careful, of course… HOT HURTS!

Insert the brewmometer through the foil, and deep enough so it hits the water. (so the brewmometer will have a chance to contact the hot water and become sterilized, as well).

Put the flask in a water bath and cool down to 100¬į F… notice that there is a trivet in the sink… that’ll allow water to circulate under the flask and help cool it a little more efficiently. No trivet, no problem… it jsut might take another couple minutes longer to reach 100¬į F.

Once it’s cooled to 100¬į F, you’re ready to sprinkle in the yeast. This recipe I used US-05 in an 11.5 gram packet, but this process will work for Mr Beer yeast packets, or any other large packet of yeast, as well. Make sure you spray the outside of the yeast packet and the scissors with sanitizer… I keep a bottle of Star San around just for stuff like this.

You’ll see the yeast granules floating on top, once you sprinkle in the dry yeast. That’s what it’s¬†supposed¬†to look like… DON’T STIR! Just let it sit. 15 minutes. Start a timer… spend the 15 mins cleaning 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. If you’re using a measuring cup, you’ll need to use a sanitized spoon to stir everything… stir gently.

Once you’ve swirled/stirred and the yeast is suspended, it’ll look kinda creamy and homogeneous… kind of like this…

And you’re ready to pitch the yeast slurry to¬†inoculate¬†the wort. Just pour the whole slurry into the fermenter. Any dilution effect from pouring the yeast +water into the wort will be compensated for by the alcohol produced during bottle carbonation… or i like to think it is.

And, yes, I know this is different than the way yeast manufacturers recommend for their dry yeasts to be rehydrated. But, guess what? I’ve used this method for every company’s dry yeast and it’s worked like a charm… Fermentis, Danstar, Mr. Beer’s “Under-The-Lid Mystery Yeast”… it’s worked fine. Lag time until fermentation begins is cut, and you’re pitching healthy, happy, alive yeast into the beer.

The process seem long, and complicated, but the whole thing… even cooling the sterile in an ice bath… takes about a half an hour. It’s simple, trust me… if I can do it, you can do it. And your beer (and those that drink your beer) will thank you.


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  1. #1 by Matt C on July 24, 2011 - 11:47 AM

    …Doing something similar on my blogsite. I write about all things to do with brewing. check it out at

  1. Simple Yeast Starter « Chunky Brewing…

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