Dry Yeast

[chrismccull]

When working with dry yeast, do you always re-hydrate it?  

I followed the instructions in 'How to Brew' and it stated that the yeast should be re-hydrated in 35-40 C water for 30 min.  Doesn't that seem rather hot?  I thought the reason why we cooled the wort was to bring the temp well below 30 C to be able to pitch the yeast?  If so, why would you re-hydrate in such hot water?

[Dave Savoie]

Ive never re-hydrated yeast I dont think anyone here actually does to be honest

[Chris Craig]

I've read in several places that re-hydrating dry yeast is important for viability.  You're going to get fermentation either way, but you get more healthy cells if you do. I usually rehydrate in 25C water for 20 minutes.  35-40 seems way to hot to me.

[chrismccull]

I thought it seemed hot also, 25 C makes more sense to me.

My understanding is that fermentation will take place more quickly if you re-hydrate.  My fermentation is very active, I had to remove the 3 piece air lock and install a blowoff tube.

[Dave Savoie]

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.

[chrismccull]

Thanks Dave, that helps a lot.

[Chris Craig]

There's lots of contradictory information out there on the subject.  In any case, I've made good beer using both methods.  So, do what makes you feel warm and fuzzy, and enjoy the result  

[Kyle]

I used to re-hydrate dry yeast until several years ago I forgot and just dumped it in. There was no noticable ill effect, so I do it that way now. Also, some manufacturers of dry yeast say re-hydration is not needed with their products.

[pliny]

Just a little comment - people should state their source when getting and sharing information from a book, the internet or any place else.

[HappyHax0r]

I used to re-hydrate dry yeast until several years ago I forgot and just dumped it in. There was no noticable ill effect, so I do it that way now. Also, some manufacturers of dry yeast say re-hydration is not needed with their products.

Unless it's nottingham, in which case rehydration makes it do it's thing... it's thing being ruining beer... *still bitter about the fusels in my stout* .

[Richard]

In the spirit of the internet, and just to chime in my blend of anecdotal and vaguely remembered contradictory information...

I find that pitching dry yeast into wort increases the lag time by two-three times, versus re-hydration.

For re-hydration, I specifically use water that's about 35C, just-boiled vigorously for about ten minutes (de-oxygenated, sanitary, and removes some of the chlorine).

I heard that re-hydration in a sugary solution such as wort will cause a large number of the yeast membranes to basically explode from osmotic pressures... and that re-hydration protects against this.

YRMV.

[Shawn]

I find that pitching dry yeast into wort increases the lag time by two-three times, versus re-hydration.

For re-hydration, I specifically use water that's about 35C, just-boiled vigorously for about ten minutes (de-oxygenated, sanitary, and removes some of the chlorine).

I heard that re-hydration in a sugary solution such as wort will cause a large number of the yeast membranes to basically explode from osmotic pressures... and that re-hydration protects against this.

YRMV.

This.

35 C (95 F) SOUNDS hot, but it's really more warm. Some people who use pool heaters in the summer keep their pool water in the high 80s F, which I think is fairly warm. I believe dry yeast won't start being killed until 120 F or so...?

[Shawn]

Just a little comment - people should state their source when getting and sharing information from a book, the internet or any place else.

And +1 to this...

[sdixon]

+1 What Dean said :-)

and... I have done both and not noticed any difference I can detect by just pitching dry yeast... so being efficient (or lazy), I pitch dry. As I understand it dry yeast these days is meant to pitch dry unless otherwise stated.

[Dave Savoie]

One less chance of an infection by dry pitching