Originally Posted by samc
You have provided absolute instructions - rigidly based upon what?
Yeasts are living organisms and rehydration temperature is critical for good yeast performance. Fermentis recommends that top fermenting/ale yeasts are rehydrated at a temperature between 25-29°C (77-84°F) and that bottom fermenting/lager yeasts are rehydrated at a temperature range between 21-25°C (69-77°F).
and Danstar says
"Sprinkle the yeast on the surface of ten (10) times its weight of clean, sterilized (boiled) tap water at 30 - 35°C (86° - 95°F)"
Who should we believe?
I do what Fermentis recommends because I use S-05, If I was to use Notty I'd follow Danstar.
You are right. I did offer some really finite instructions that might clash with some of the conventional wisdom on this board. Who should you believe? As you mentioned, if you were to use Notty, you'd follow Danstar. I am happy you feel that way, because everything I outlined comes directly from a Q&A interview with Dr. Clayton Cone of Lallemand (Danstar). He is more qualified to explain than I am.
I try to avoid the "and here is the link to prove it" in my posts, but since you asked...http://koehlerbeer.com/2008/06/07/rehydrating-dry-yeast-with-dr-clayton-cone/
It is a great read. I wish more people would see it. It is from a scientist who works for the yeast manufacturer - can you get a more expert opinion? I guarantee he is a better authority on the subject of yeast health than anyone on the board, and he basically addresses every myth that I see proposed about using dry yeast. Please read for yourself and then we can revisit.
For those from the too-lazy-to-click-and-read camp, here are two quotes I'll cut and paste, specific to what my "absolute instructions" are "rigidly based upon."
Using 100F to rehydrate....
"Every strain of yeast has its own optimum rehydration temperature. All of
them range between 95 F to 105F. Most of them closer to 105F. The dried
yeast cell wall is fragile and it is the first few minutes (possibly
seconds) of rehydration that the warm temperature is critical while it is
reconstituting its cell wall structure."
1/2 of dry pitched cells die.......
"As you drop the initial temperature of the water from 95 to 85 or 75 or 65F
the yeast leached out more and more of its insides damaging the each cell.
The yeast viability also drops proportionally. At 95 – 105 F, there is
100% recovery of the viable dry yeast. At 60F, there can be as much as 60% dead cells."
He goes on about wort starters for dry yeast.....
"For the initial few minutes (perhaps seconds) of rehydration, the yeast
cell wall cannot differentiate what passes through the wall. Toxic
materials like sprays, hops, SO2 and sugars in high levels, that the yeast
normally can selectively keep from passing through its cell wall rush right
in and seriously damage the cells. The moment that the cell wall is
properly reconstituted, the yeast can then regulate what goes in and out of
the cell. That is why we hesitate to recommend rehydration in wort or
must. Very dilute wort seems to be OK."
Finally - "but I always just sprinkle it on top!"
"How do many beer and wine makers have successful fermentations when they ignore all the above? I believe that it is just a numbers game. Each gram of Active Dry Yeast contains about 20 billion live yeast cells. If you
slightly damage the cells, they have a remarkable ability to recover in the
rich wort. If you kill 60% of the cells you still have 8 billion cells per
gram that can go on to do the job at a slower rate."
EDIT - Fermentis does have a seperate set of instructions for the craft beer industry than they offer to homebrewers. Pretty insulting if you ask me. Here is the link if anyone has not been able to find it.http://www.fermentis.com/fo/pdf/Tips-Tricks.pdf