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Old 04-14-2008, 12:45 AM   #1
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Default Rehydrating dry yeast not necessary....

This is quoted from Winexpert and it applies to Beer as well as Wine:

Q: What is the best way to handle the yeast?

A: If you look at the instructions in your wine kit (and please, do), they will likely instruct you to sprinkle your packet of yeast directly on to the must. Yet if you read the yeast package (and many winemaking textbooks) they recommend rehydrating the yeast. If the objective is to deliver the maximum number of yeast cells to the must, which technique is best?

It turns out that the answer is not as simple as one or the other, but the main point is that rehydration is not really necessary. You can rehydrate your yeast if you absolutely want to, but be sure to do it accurately and precisely, as explained further below. The rest of us will tear open the package and dump it in, and spend the extra time sampling our last batch!

When performed correctly, rehydrating gives the highest live cell counts, and the quickest, most thorough fermentation. The catch is, it has to be done precisely correctly. Lalvin EC 1118 champagne yeast, for instance, asks you to add the yeast to 10 times its weight in water at 40-43°C (104-109°F).

Breaking it down, the amount of '10 times' is important if you're trying to maximise live cell counts. That's because the yeast is dried on a substrate of nutrients and sugars. At a ratio of 10:1 water/yeast, the osmotic pressure allows for maximum nutrient uptake (osmotic pressure is influenced by the dissolved solids in the water, like nutrients and sugars). If too much water is used, the yeast will grow only sluggishly. If too little water is used, the cells may burst from the flood of liquid and nutrients forced into them.

Secondly, the temperature range is inflexible. The outer integument of a yeast cell is made up of two layers of fatty acids. These layers soften best in warm water, much as greasy film will come off of dishes best in warm water. Once it has softened up, it will allow the passage of nutrients and waste products in and out of the cell much more efficiently. If the water isn't warm enough, the cell won't soften. If it's too warm, generally anywhere above 52°C (125.6°F) the yeast cell will cook and die.

The next thing you have to worry about is temperature shear. Yeast is terrifically sensitive to environmental conditions. If it goes too quickly from a favourable temperature to a less favourable one, weakened cells may die, and others may go dormant, in an attempt to ride out the temperature shift. This reduces the numbers of live, viable cells available to ferment the must, and gives spoilage organisms a chance to get a foothold, and potentially ruin your wine. So if you are rehydrating your yeast, you'll have to wait as the yeast cools to within two degrees of your must temperature before adding it: accuracy counts!

On the other hand, simply dumping the yeast onto the top of the must should result in lower cell counts. Empirical evidence shows this isn't the case: the yeast appear to know what they're doing. Generally, a five-gram packet of yeast will have less than a six-hour lag phase on an average wine kit. This is perfectly acceptable, and isn't long enough to allow spoilage organisms to get a foothold in your wine. Plus, it's a heck of a lot simpler than going through the rehydrating process, fraught as it is with risks.

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Old 04-14-2008, 12:48 AM   #2
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Thanks for the article Forrest. I always forget to rehydrate and half the time just pitch it dry. Good to know I am not a total screwup.

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Old 04-14-2008, 01:02 AM   #3
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While the ideal rehydration procedure does take temp and water volume into account, getting it close is better than not at all. I mean, I did side by side batch experiments and the rehydrated yeast samples all started fermenting about 4 hours earlier than the dry pitch. I don't know what that means in actual number of cells but I know it's more.

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Old 04-14-2008, 01:14 AM   #4
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I'd agree that it's not necessary, although it's certainly not going to hurt.

Personally, I never rehydrate dry yeast and Nottingham usually takes off within 8 hours for me.

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Old 04-14-2008, 01:53 AM   #5
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I agree with Bobby. I think the bottom line is: properly rehydrated yeast (or at least close to "properly") will always yield more viable cells. Plus it will help reduce the number of dead cells going into the wort. I believe bakers recommend rehydrating yeast for the same reasons.

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Old 04-14-2008, 02:32 AM   #6
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Did my first two brews simply pitching the yeast dry, did the last few rehydrated and I have been happier rehydrating. I have less lag time, and and it seems to me I get a more active fermentation. YMMV.

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Old 04-14-2008, 05:24 AM   #7
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I think this discussion is largely missing the boat here. Yes, if you fail to rehydrate your dry yeast it will still perform and ferment your beer. But recognize that the major yeast manufacturers all state that you will lose some proportion of your yeast cells by not rehydrating properly. Typical figures are between 40 and 60%.

For lower gravity beers, that may still be enough yeast to get the job done adequately. But if you are brewing something bigger, your ferments are going to be slow and protracted, leading to poor attenuation and possibly off-flavours in the beer. The best strategy is to pitch a higher number of yeast cells. So, one can either rehydrate to keep the cell count up, or skip rehydrating and pitch more yeast (e.g., two packs) instead. The tough part with the latter option is that it is hard to guess at how many yeast cells will be damaged/killed by not rehydrating properly, making it difficult to judge how much yeast you need for moderate- to high-gravity brews.

So while not rehydrating will still make beer, the implications of this on the QUALITY of the final beer should be explored. The starting place should always be determining HOW MUCH yeast is actually required, and then you can pick your strategy (i.e., to rehydrate or not) from there.

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Old 04-14-2008, 05:27 AM   #8
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sounds like a whole lot of wasted effort. Ive never rehydrated dry yeast and never had a lag time longer than 6hrs.

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Old 04-14-2008, 05:30 AM   #9
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Quote:
The tough part with the latter option is that it is hard to guess at how many yeast cells will be damaged/killed by not rehydrating properly
At no time did it say that you are killing cells by directly pitching. It say you can cook them at 125° or above.
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Old 04-14-2008, 05:37 AM   #10
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Quote:
Originally Posted by MikeFlynn74
At no time did it say that you are killing cells by directly pitching. It say you can cook them at 125° or above.
I wasn't quoting the article above by Forrest. I was referring to common knowledge about the effects of pitching dry yeast directly into wort. The temperature issues are an ADDITIONAL source of mortality for dry yeast.
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