Can too high rehydration temperature cause off flavours?

[aidan]

I usually sprinkle my dry yeast directly on the wort but I decided to give rehydration a go since I was doing a pilnser and higher yeast count is more critical for cooler ferments. I followed some online instructions (http://www.homebrewers.com/c=kQ4e1C...ks.videos.001_beginner.rehydrating_dry_yeast/) that stated to rehydrate at 105°F/40°C. This is the rehydration temp that I've read in many other places. My actual temp was 99°F/37°C. Everything went well and fermentation (at 55°F/13°C) was going strong within 12 hours.

Afterwards I checked the Fermentis data sheet for my yeast, S-23, and saw that it advised rehydration at 27°c ± 3°C (80°F ± 6°F). Thats a HUGE difference!!! Well I know that it still worked at 99F/37C but I'm wondering if there is some downside? Could the higher than recommended rehydration temp cause some unwanted side-effectes such as off-tastes etc?

 

[duboman]

Basically, no. Off flavors are created during the growth phase which begins when the yeast begin consuming the oxygen and sugars in the wort, not from simply being rehydrated

Now the importance lies in the actual fermentation temperature of the wort.

 

[aidan]

Basically, no. Off flavors are created during the growth phase which begins when the yeast begin consuming the oxygen and sugars in the wort, not from simply being rehydrated

Now the importance lies in the actual fermentation temperature of the wort.

That's what I figured. But I'm still left wondering what's the explaination for the massive difference in the rehydration temperature recommended by Fermentis and most other sources? And what's the penalty for going way over their guidelines? 80°F vs 105°F - were not just talking a few degrees here!

 

[aidan]

I should have asked the question as 'Are there any negative effects of rehydrating at higher temperature than manufacturers guidelines?'

 

[Wynne-R]

rehydration instructions (S-04, S-05)

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.

rehydration instructions (S-23, W-34)
Sprinkle the yeast in minimum 10 times its weight of sterile water or wort at 23°C ± 3°C (73°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.

Actually, it’s 80F for the ale yeast, it’s 73F for the lager. White and Zainasheff say 95-105F, but mention some manufacturers recommend lower temperatures.

I have done both with S-04 and I find more action with warm water. Maybe too much. “Yeast” warns that at warm temperatures yeast quickly use up their energy reserves.

I think that’s the trade-off. If you use warm water, be quick about it. But then again, “Yeast” cautions to get within 5F of your pitching temp.

 

[GuldTuborg]

I should have asked the question as 'Are there any negative effects of rehydrating at higher temperature than manufacturers guidelines?'

There can be, yes. If you don't rehydrate properly, you can kill off a good portion of your yeast, leading to underpitching, and I'm sure you know the rest. I can't tell you what percentage of yeast will die at what temps, but I know the information is out there somewhere.

 

[aidan]

Ok, so what accounts for the massive difference in what fermentis recommends, 73F, and what other sources (e.g. White and Zainasheff, 95-105F) recommend?

 

[Wynne-R]

They’re French. Seriously, I think it’s a dumbed down idiot proof thing.

If you can hydrate warm and cool it quickly, go for it. Otherwise take an hour and do it their way.

 

[aidan]

They’re French. Seriously, I think it’s a dumbed down idiot proof thing.

Their 'dumbed down idiot proof' instructions on the back of home brewer sized sachets are to sprinkle directly on wort. But their data sheet is aimed at the commercial brewer so I don't buy that it's just dumbed down instructions. There's got to be a better explaination

 

[BigFloyd]

I think it would be helpful to know, since S-23 is a lager yeast, what your pitch and initial (first 4-5 days) ferment temps were for this batch.

Also, after rehydrating, did you "attempurate" the yeast slurry to within 10*F of the wort before pitching?

 

[aidan]

I think it would be helpful to know, since S-23 is a lager yeast, what your pitch and initial (first 4-5 days) ferment temps were for this batch.

Also, after rehydrating, did you "attempurate" the yeast slurry to within 10*F of the wort before pitching?

Pitch temp 15C, ferment temp 13C. Attemperated yeast slury to 23C prior to pitching. Most instructions say it should be within 10C NOT 10F

 

[aidan]

Ok, I drawn my own conclusions and have come to my own theory to explain this: I do not think it is due to any difference in the type of yeast or the drying process compared to other manufacturers. I reckon that Fermentis have determined that a temperature much lower than the traditionally recommended 105°F/40°C works just as well for hydrating yeast. You just need to give it a longer time to rehydrate - 30 minutes instead of 15 minutes. The temperatures that they recommend are within 10°C of pitching temperature so that there is no need to attemperate. This explains the difference between their recommended rehydration temperatures for lager and ale yeasts.