rehydrate first or?

[yeastforbrains]

The question about whether rehydrating dry yeast in water versus sprinkle directly on wort has already been discussed so many times and in so many ways that it is difficult to justify a new post on the subject. Yet, there's no way back now, if you read this, it is posted, justified or not.
The reason I post is I am not satisfied with the existing explanations. I never come across any real easy and yet plausible explanation to why wort can damage the dry yeast, or why one can seemingly still get away with sprinkling directly. Voila, this is my self-granted entrance ticket to the subject, this is where I will try to tackle the justification point.
It has been scientifically proven that sprinkling directly in wort instantly kills off 50% of the cells you are pitching.
So, why does rehydrating in water result in so much healthier yeast count?
This leads to another question -> what was removed from the yeast when it went through the dehydration process? The answer is of course, water.
So to bring this dormant, dried, but still living organism, back to its original state, the natural instinct should be to put back what was removed in the first place; not milk, not mustard, not lemon juice, not wort, but pure water. Rehydrating it in any other "unpure" liquid, you will naturally risk poisoning or mutate the cell. At the moment of rehydration, the dried cell is a non-selective sponge, sucking in whatever liquid it has contact with, not caring if it is water or poison.

Ok then, so why on earth sprinkle directly on top?
Obviously, this method removes some time and infection risks from the process. To rehydrate in an adequately sanitized or sterile manner, you will have to boil water and cool it down in a sterilized/sanitized vessel. Then add the yeast, then wait 30 minutes, then gradually introduce wort to dilute the temperature difference etc. It's not a simple question of taking a dishwasher clean cup from your cabinet, adding lukewarm tap water, swirl and pitch. If you do it properly, it takes time and is quite a bit of a pain.
Also, what do you gain in terms of end results? Here there's no decisive conclusions to pull from any objective sources. People who tried both claim they get good results with both methods. Hard to tell any difference, even when pitching the same amount of yeast in both cases. People who tried both, seems to prefer sprinkling directly on wort.
I haven't seen any good explanations to why this is. I have however read that dead yeast makes an excellent nutrition for living cells, but is it so excellent that it could void the difference in (healthy cells) pitch rate, and justify the mass-murdering act of sprinkling directly to wort?

 

[Cyclman]

It is about temperature that is most "comfortable" for dry yeast. They love to re-hydrate at 100 degrees. Not so much at 60 degrees, many of the yeasties will be killed off.

Ultimately, both worts will ferment into beer. But how many esters, and other undesireable compounds result in the interim?

 

[losdesviados]

Fermentis states that US-05 likes 80 degree water, they go on to say plus or minus 6 degrees, bringing it down to 72 degrees a rather pitchable temperature.


From Fermentis on US-05
rehydration instructions
Sprinkle the yeast in minimum 10 times its weight of sterile water or wort at 27°c ± 3°C (80°F ± 6°F). Leave to rest 15 to 30 minutes.
Gently stir for 30 minutes, and pitch the resultant cream into the fermentation vessel.
Alternatively, pitch the yeast directly in the fermentation vessel providing the temperature of the wort is above 20°C (68°F). Progressively sprinkle
the dry yeast into the wort ensuring the yeast covers all the surface of wort available in order to avoid clumps. Leave for 30 minutes, then mix the
wort using aeration or by wort addition.

 

[g-star]

Read a textbook, and don't rely on Internet message board "sources", which are often uneducated people parroting bad information that aligns with some pre-conceived paradigm.

I recommend starting with "Yeast" by White & Zainisheff. You'll find all of the proven reasoning as to why dry yeast should ALWAYS be re-hydrated.

 

[Shooter]

I don't boil water to rehydrate. I sanitize a cup with StarSan and use bottled spring water. I nuke for about 10 seconds, check the temp. If too warm, add more bottled water. If too cold, nuke again, repeat until temp is around 80 degrees, proceed with rehydration.

 

[TalkingGoats]

Re-hydrating helps the weaker cells survive work. Make 2 beers side by side, rehydrate one and pitch the other directly. You'll probably notice the rehydrate batch tastes cleaner and what not. Its one step I leave out if I use US-05 though, never a bit of difference IMO.

Comparable to getting roused out of bed slowly, as opposed to someone screaming at you to do your job from a dead sleep.