Can anyone tell me what is the proper tempurature for pre-mixing fresh compressed yeast prior to making dough? Throughout many posts, I have read many different and contradicting things.
After reading this post I began to think about this so I Googled it and was suprised to find a ton of conflicting advice. I have read anywhere from 100 to 130 some say under 110 is too low but all say over 130 is too high. The general average that I found suggested a mean temperature of 110. I have been doing my yeast at 100 for the last 4 years and it seems to work for me so that is what I am going to stick with.
Thanks for the info guuys. Right now I’m mixing the yeast in 95F water for about 10 minutes. I’ll try raising the tempurature to 105F and see the difference. 
Above about 110-115 degrees you will kill the yeast. The mixing process adds heat to the temp you start with.
The temp you want depends on several things. How soon you want to use the dough makes a difference. We use the coldest water we can get. In the summer we may put a bucket of water in the walk-in over night to get it colder. By using cold water we slow down the action of the yeast and extend the useful life of dough.
We make the dough in the morning. Ideally, we will use the dough the following night but if we are busier than expected we CAN use it that same night. It also is usable the 3rd night. Generally we have two days dough on and after we make dough which gives us a lot of flexibility.
If you make dough with 100 degree water the yeast action will be fire right up. Great if you want to use the dough in a couple of hours, not so great if you might need to keep it awhile.
“Instant cell death” for yeast occurs at around 143 degrees F. Between about 115 degrees F and 143 degrees F, the damage to yeast depends principally on the time at which the yeast is held at the elevated temperature. If flour and other dry ingredients are promptly added to the water/yeast mixture, the dry ingredients will buffer the yeast and reduce further damage. This discussion as to cake yeast and IDY should be academic (except for VCM applications) since the damage to these forms of yeast can be avoided by simply adding them to the flour and other dry ingredients, as Tom regularly suggests. When cake yeast and IDY are blended in with the flour, especially if done a short time before using (to initiate hydration in the case of IDY), the flour buffers the yeast and, as a result, the tolerable water temperature can be as high as 130 degrees F. I have gone as high as 135 degrees F in experiments with IDY without noticeable damage to the yeast.
ADY is another story since it has to be rehydrated in warm water, at around 100-115 degrees F, and for about 10-15 minutes. Consequently, it is important that the water temperature be within the above range. Material deviation outside of this range, on either the low side or the high side, can result in degraded yeast performance.
Another point to keep in mind is that modern strains of yeast are hardier and resist temperature better than their counterparts of years past. Nonetheless, it is still prudent not to shock yeast with direct contact with excessively cold water or overly warm water or let them sit too long in water along with salt and sugar.
PN
I have taken this question to mean what temp you activate the yeast at rather than what temp of water you use in the dough. These can be two completely different things and should not be confused. In the reading that I did earlier this is what I found.
To determine the water temperature you need for a dough with a preferment, the formula is:
water temp = (4 x desired dough temp) - room temp - flour temp - preferment temp - mixing friction
For example, if the desired dough temp = 76, room temp = 70, flour temp = 69, preferment temp = 71, and mixing friction = 40, we can calculate:
water temp = (4 x 76) - 70 - 69 - 71 - 40 = 54
For a recipe without a preferment, the formula is:
water temp = (3 x desired dough temp) - room temp - flour temp - mixing friction
There is no need to pre-suspend fresh/compressed yeast prior to addition to the dough. The recommended way to add it is to just crumple it right into the flour just before you begin mixing the dough. ADY should be hydrated in 100 to 105F water for 10-minutes, and IDY, while it is not recommended that it be pre-hydrated (it is added directly to the flour), when the dough will be mixed for less than 4-minutes, such as when using a VCM, it does need to be pre-hydrated in 95F water for 10-minutes before addition to the mixer.
Tom Lehmann/The Dough Doctor
Thank you for the information guys. And Tom, I will try the method you mentioned. One question though, will the yeast be absorbed entirely in the dough batch? What I mean is, will it be evenly distributed in the batch?
Yes it will. It will be uniformly distributed through out the entird dough mass. I’ve done it literally, thousands of times.
Tom Lehmann/The Dough Doctor