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Old 01-24-2010, 03:25 PM   #1
Aug 2009
Posts: 31

I understand that dry yeast viability is improved with rehydration prior to pitching (according to Jamil anyway).

To re-hydrate I boil 1 cup of water to sterilize and then cool off tin foil covered in a pyrex measuring cup. When the water is below 80degF. I sprinkle the yeast into the water to rehydrate.

The last two times I've done this with S-05 the yeast formed a barrier at surface and even after letting it sit for 1/2hr a major portion of the yeast required stirring to incorporate into the water. It was clumpy and needed stirring to produce a slurry.

When I've done this with S-04 the yeast immediately falls into solution and produces a foamy slurry without stirring within 15 minutes.

Is this a common experience with this yeast?

Do you even bother rehydrating with this yeast.

After 12 hours in primary the airlock has started bubbling every 15-20 seconds so I'm guessing everything is OK. My last beer was fermenting vigorously after 24 hours. I just wonder if I really need to sweat this detail to produce great beer.
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Old 01-24-2010, 04:39 PM   #2
menschmaschine's Avatar
Jun 2007
Posts: 3,272
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Originally Posted by daveyohill View Post
I understand that dry yeast viability is improved with rehydration prior to pitching (according to Jamil anyway).
This is true and here's why...

When yeast ferment certain sugars (such as maltose), they must first secrete an enzyme that breaks this sugar down so they can metabolize it. They only have the capacity to secrete these types of enzymes when they are healthy and hydrated. Under these circumstances, the yeast's cell membrane won't allow maltose in unchecked.

When a dehydrated yeast cell first becomes hydrated, it allows too many things in the hydration solution into the cell unchecked. When it allows things in that it would normally break down first (e.g., maltose), it can die. This is why it's best to rehydrate in water first. It gives the most viability and cell count.

That being said, it's not black and white and plenty of yeast survive when rehydrated directly in wort. In the case of ales, it is often desired to have a flavor profile that comes from yeast characteristics (esters, etc.). Many of these compounds are produced during the growth phase. So, having a higher cell count, such as that which comes from rehydrating dried yeast in water, is not always considered necessary depending on the brewer and the intended beer.

In the case of S-05, you may want a relatively clean flavor profile, so it may be worth rehydrating... especially if the gravity is over ~1.040.

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Old 01-24-2010, 05:49 PM   #3
david_42's Avatar
Oct 2005
Oak Grove, Oregon, USA
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Most yeasts just sit there. The explanation I've received is: dry yeast is extremely hygroscopic and sticky. Even sitting on top of the water, the yeast is absorbing water. Next time I use some S-04, I'll try to remember if it acts differently.
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Old 01-25-2010, 01:14 AM   #4
Irrenarzt's Avatar
Aug 2009
Half a mile from Tucson
Posts: 2,106
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S05 is an animal, I wouldn't bother rehydrating.

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Old 01-25-2010, 04:19 AM   #5
denimglen's Avatar
Feb 2006
Auckland, New Zealand
Posts: 438
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I have this 'problem' as well.

The effect is reduced if you can rehydrate in a container that is shallower and wider so there's more water surface area touching the yeast.

I just use a pyrex beaker, after about 15 minutes I give it a good stir, and again after about another 5 minutes then pitch., haven't had any problems yet.

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Old 01-25-2010, 04:46 AM   #6
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CharlosCarlies's Avatar
Jan 2009
Conroe, TX
Posts: 713
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Happens to me every time as well. I just give it a gentle swirl after 15-20 min and it's ready to go in another 5-10.

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Old 01-25-2010, 05:34 AM   #7
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defenestrate's Avatar
Sep 2008
edgewater, MD
Posts: 1,043
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same thing here. when i use s04 it blooms up real quick, and notty precipitates very quickly. no biggy.
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Old 01-25-2010, 01:12 PM   #8
Aug 2005
Philadelphia area
Posts: 1,573
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I don't rehydrate it at all and I've never had a problem. I'm careful to get my wort to the right temperature before pitching.
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Old 01-25-2010, 02:07 PM   #9
greenbirds's Avatar
May 2008
Posts: 463
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Yes, I have noticed this as well. Seems pretty much impossible to execute the instructions as stated (suspend without stirring while it soaks up water, then stir after ~15 min). I think denimglen hit it right on about using a shallower, wider container.

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Old 01-25-2010, 02:30 PM   #10
Cycling + Beer
Aug 2008
Santa Maria, CA
Posts: 67
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Viability of the yeast is lower without re-hydrating properly. There still are enough active yeast to ferment, but you are also essentially throwing a bunch of sick or dead yeast in your beer. I prefer not to do that.

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