A Dry Yeast Rehydration Experiment

Sorry if they were too numerous, but often it seems I need to re-clarify what I already said. I already did say above that I would post there, once I have looked into it a little more deeply for the reason posted above.

 

Yes. The first package was sprinkled on the surface as directed on the package itself, and the second package was rehydrated exactly as directed in the specification sheet at the Fermentis site and added the next day. I tried to cover both options.

 

You may have had 'better' results if you rehydrated a total of two sachets exactly how it is detailed on the Fermentis data sheet.

For the one sachet you rehydated did you do it this way:

“REHYDRATION INSTRUCTIONS: Sprinkle the yeast in minimum 10 times its weight of sterile water or wort at 21 to 25 °C (70°F to 77°F). Leave to rest 15 to 30 minutes. Gently stir for 30 minutes, and pitch the resultant cream into the fermentation vessel.”

Cheers!

 

In hindsight (I had no prior experience with dry lager yeast) I agree that rehydrating both packages would have been far preferable.

Not exactly. I wondered whether this instruction would result in shocking the yeast, since I was fermenting at 50 F (initially I was intending to ferment at 48 F). Dropping the yeast 20 - 27 degrees F would likely shock the yeast. Thus after reading the rehydration instruction sheet, I went back to the Fermentis site and read their Q&A tab. Someone else had the same concern as I did about shocking the yeast, so I read:

"I see the recommended rehydrate temp for ale yeast is 25~29°C? My pitching temp for ale is 18°C. Will this not "stun" the yeast?
The recommended rehydrate temperature is an optimal temperature.

Outside this optimal range (as long as the temperature is above 10°C), you will not stun the yeast but you could get a longer lag phase at the beginning of the fermentation.

Of course, this point is depending of the others factors influencing the fermentation (quality of the wort, fermentation temperature, starting gravity, etc…)."

So, instead of rehydrating the yeast in 70 - 77 F water or wort, I rehydrated it in 55 F wort. At that temperature, it took a lot of stirring to 'de-clump' the yeast. After 30 minutes, I pitched it into the carboy.

So the only difference was that I rehydrated the yeast in wort that was at a lower temperature than in the unqualified instructions.

 

I am not a microbiologist that works for Fermentis but permit me to opine that you may have caused issues here.

My understanding of following proper (specific) instructions for rehydration is that you want to optimize the number of viable yeast cells. For the sake of argument let's say that a fresh sachet of 11.5 gram Fermentis dry yeast contains 230 billion yeast cells (i.e., 20 billion live yeast cells per gram). The hope is that by properly rehydrating (i.e., following the yeast vendor's rehydation instructions to the letter) the net result is that all of those 230 live yeast cells are completely viable in the yeast cream and are ready to start fermenting. Needless to say but you would want the yeast cream after the one hour process to be within 10 degrees C (18 degrees F) from the wort for pitching to mitigate "yeast shock". So, if one were to sprinkle the dry yeast on top of 73 degrees F water you would not want the yeast cream after the one hour process to be no more than 68 degrees F for a 50 degrees F wort). I personally would have problem having that occur in my homebrewery.

What percentage of the dry yeast is completely viable when instead somebody decided to rehydrate in 55 wort (which is not water)? Needless to say I do not have a specific value to offer here but I would be willing to bet it is significantly less than if the dry yeast was rehydrated properly (i.e., 73 degrees F sterile water).

Given what you stated in post #64 I am personally not too surprised it took you two days to see signs of fermentation.

Cheers!

 

Although I agree with you theoretically, there are always trade-offs when brewing beer, and other considerations are not often thought of. The trade-off is not rehydrating the yeast at the initially suggested warmer temperature, as I did. Had I rehydrated at 73 F, and then pitched the yeast in wort 20-27 degrees cooler than the rehydration temperature, how many yeast cells would I have shocked? Possible even more than the yeast cells that become viable at the higher temperature? Why does Fermetis even mention using a lower temperature (no lower than 50 F) if they weren't concerned about yeast shock? There's no chart that tells me what is the optimum temperature to rehydrate so that I lose the least number of cells to either lack of viabilitty, or to cell shock? So I logically chose to rehydrate at 55 F. Maybe next time I can try 60, or 65, or whatever, until I find an optimum temperature for the least number of cell lost that no chart can currently provide. There's unlimited information about brewing ales, and lots of forgiveness in the results, but so little concerning lagers, and so very little forgiveness.

So my guess is that the optimal temperature for rehydrating the yeast (i.e. resulting in the maximum number of viable yeast cells) - for lagers fermented at about 50 F - is NOT 73 F, but somewhere between, say, 55 F and 73 F. What it actually is, is anyone's guess - until several experiments have suggested otherwise.

The two days are possibly related to three factors - 1) sprinking the first yeast package instead of rehydrating and 2) not using more than two packages of yeast, and 3) not rehydrating at a somewhat higher temperature (perhaps 60 F instead of 55 F ?).

 

I am not following you here.

The optimal conditions to rehydrate S-189 yeast are:

• 10X weight of sterile water
• 70°F to 77°F

You did neither of the two items listed above.

The next step is to not pitch the yeast cream into wort that is colder by a difference of 18 degrees F (10 degrees C). You stated: "I was fermenting at 50 F". So, you would want the yeast cream's temperature to be no higher than 68 degrees F when you pitch it. Permitting the rehydrating yeast to cool down from say 73 degrees F to 68 degrees F over the one hour rehydration process is not an onerous step.

Cheers!

 

"The next step is to not pitch the yeast cream into wort that is colder by a difference of 18 degrees F (10 degrees C). "

What is the justification for this? Chris White (from White Labs) and Jamil Zainasheff, in their book "Yeast" suggest that, in order not to send the yeast into dormancy, the temperature must be lowered by no more than about 1 to 2 degrees F per day (see page 115).

 

From Lallemand (Danstar): “Temperature shock, at greater than 10°C, will cause formation of petite mutants leading to long-term or incomplete fermentation and possible formation of undesirable flavors.”

You want the rehydrated yeast to be within a 10 °C (18 °F) temperature agreement to not cause the formation of petite mutants. In other words if you are pitching rehydrated yeast into 50 °F wort, make sure the rehydrated yeast is no warmer than 68 °F.

Cheers!

 

That seems like a huge differential. Does what applies to Lallemand (generally wine yeast) apply to Fermentis? Is an 18 °F difference at typical (higher) wine fermentation temperatures different than the lower fermentation temperature ranges of lagers? Although Fermentis's response about yeast shocking is incredibly vague, it does suggest that yeast shock can occur, so that the rehydration temperature can be as low as 50 F to prevent this. And beside the issue of yeast shocking is the issue of yeast dormancy.

There still seems to be more speculation and vagueness than concrete guidance.

Perhaps another email to Fermentis is in order.

 

I'm not inclined go much over 1.065 or so, but that's an arbitrary number. Up to 1.080-ish, I'll rehydrate. Above that, I'll use two packets or, more likely, a cake from a previous batch.

 

If you look at the new E2U .PDF that Fermentis recently published, the recommended temperature for rehydration of S-1S9 is 59-77F. The lower range would avoid thermal shock. The old range can still be found.

From the product page too.
"
With prior rehydration:

Alternatively, sprinkle the yeast in minimum 10 times its weight of sterile water or boiled and hopped wort at 15 to 25°C (59°F to 77°F). Leave to rest 15 to 30 minutes, gently stir and pitch the resultant cream into the fermentation vessel."


https://fermentis.com/en/fermentation-solutions/you-create-beer/saflager-s-189/

 

Where, in any literature (other than Lallemand as Jack provided above) does it say that yeast at 59 F won't be shocked if you suddenly drop it in (for example) 48 F wort, a typical lager fermentation temperature? How much range of temperature can yeast withstand (suddenly) at the lower temperature ranges? Why does the Yeast book recommend that yeast should only be dropped by a couple of degrees - per day, in order to avoid dormancy?

 

Just the common knowledge, which may be wrong. i have often heard 10F as the difference. It is also said often that the yeast are more tolerant of going from low to high temp.

It has been a while but the Yeast book is talking about the end of fermentation, where the yeast are getting ready to go dormant IIRC.

 

That's my recollection also.

 

It sure would be nice to have some source on this. I've also heard that "rule" but never knew where it came from, and whether or not it's just another of those numerous "beer myths"

 

I gave you a source: Lallemand.

 

But you didn't read my response to that. Number 1, unless I'm wrong, Lallemand primarily makes wine yeast, and I beleive some ale yeast. Number 2, wine, or ale is fermented at a much higher temperature than a lager. Thus the difference in temperature for a wine or ale yeast at a higher temperature (e.g. dropping from 70 F to 60 F) may not make as much difference as a lager yeast, dropping from 55 F to 45 F.

I'm specifically talking about lager yeast and the drop in temperature in the 55 F to 45 F range.

In short, while a 10 F drop in temperature for a wine or ale yeast at a fairly warm temperature may not be so critical, how critical is it for a lager yeast at the 55-45 F range?