Should I Re-hydrate Dried Yeast?

[nala]

Only ever sprinkled,never had a problem, ah well, time for a change then.

 

[Ducatiboy stu]

Only ever sprinkled,never had a problem, ah well, time for a change then.

I am surprised that you managed to make beer at all with out re-hydrating your dried yeast, unless of course you followed the instructions on the pack to sprinkle it on......

 

[danestead]

I am surprised that you managed to make beer at all with out re-hydrating your dried yeast, unless of course you followed the instructions on the pack to sprinkle it on......

Maybe he was brewing according to the Reinheitsgebot of 1516 and just let nature do what it wanted.

 

[Ducatiboy stu]

Maybe he was brewing according to the Reinheitsgebot of 1516 and just let nature do what it wanted.

Good point

 

[tavas]

....um....well.........because this is the internet...?

Yeah sorry, I don't know what came over me, trying to use logic in a yeast rehydrating debate. Clearly I'm an amateur at this interwebs thingy

 

[Ducatiboy stu]

Yeah sorry, I don't know what came over me, trying to use logic in a yeast rehydrating debate. Clearly I'm an amateur at this interwebs thingy

Yes, well using logic in a yeast debate is a rookie mistake....

 

[GalBrew]

Yes, well using logic in a yeast debate is a rookie mistake....

Very true.

 

[Goose]

Its not cutting corners of it makes no difference at the end of the day.

Its just a matter of which 2 methods you want to use

Isn't this all about a viable starting cell count in the pitch ?

I have really screwed up by underpitching dried yeast before. Ive detailed it on an S-189 thread but my case was a little more complicated as I saw no difference in rehydrating or sprinkling to the end result. I later realised it was because i was underpitching using both methods. And I was underpitching because I omitted to include the manufacturers' minimum viability specification in my calculations as it varies significantly by strain.

the learning for me after a stack of wasted double batches was never underpitch.

dry pitching may well give you that required cell count, even if a bunch of them die in the process of waking up. So it still works in the end, IF you pitch enough of it.

it seems to me there is at least some evidence out there that rehydration increases starting viable cell count, so your chances of hitting that required threshold are higher, if you do.

 

[Ducatiboy stu]

Think of the kittens.....

 

[Ducatiboy stu]

the learning for me after a stack of wasted double batches was never underpitch.

Also true of liquid or any other form of yeast

 

[tavas]

it seems to me there is at least some evidence out there that rehydration increases starting viable cell count, so your chances of hitting that required threshold are higher, if you do.


If you correctly rehydrate

 

[danestead]

it seems to me there is at least some evidence out there that rehydration increases starting viable cell count

I think it is fairly common knowledge that this is the case and that isn't what is being debated.

I think the debate is misunderstood. I posted above that I think the debate is actually about whether people think the extra effort of rehydrating and the extra risk of infection is worth the extra viability you achieve.

so your chances of hitting that required threshold are higher, if you do.

In a way I agree with that, and in a way I don't. My assumption, and it is in fact an assumption, is that when rehydrating, you will end up with a more consistent % of viable yeast cells. That is, and I'm making up numbers, you may have a 85-90% (small range of percentages) viable count when rehydrating. If sprinkling, I think the spread would be greater, and again I'm making numbers up, but between 25-40% (large range of percentages, in fact, 40% is almost double 25%) viable cells. In that regard I think you will find it harder to pitch an accurate number of yeast cells when sprinkling as it's quite a broad range.

On the other hand, I have a mate who is a sprinkler. He pitches an extra packet of yeast because he knows that sprinkling results in less viable yeast. So in his belief, he is still pitching a correct quantity of viable yeast due to the extra he added as opposed to rehydrating.

 

[Moad]

Sorry if this has already been posted. I googled "rehydrate yeast science"

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2011.tb00482.x/epdf


Conclusion

"It is clear from this study that the method of rehydration may play a particularly important role in maintaining popula-tion health and yeast slurry viability. Specifically, incom-plete rehydration, or rehydration at a sub-optimal tem-perature, is likely to result in impaired viability. While the current study has focused on the rehydration of yeast un-der laboratory conditions, these results may indicate that directly pitching ADY into wort (particularly cooler, lager type worts) could potentially result in viability loss and negatively influence fermentation performance. Further-more, it is suggested that the optimum temperature of rehydration should be determined for each individual ADY strain and that these guidelines should be applied in the brewery in order to help ensure yeast viability and final product quality."




There are still corners of the square as it was put earlier, the temperature of the rehydration liquid is just as important as whether or not to rehydrate. You could be doing more damage by rehydrating at the wrong temp.

Personally I find the risk does not justify the reward. It might be my palate but I found no discernible difference rehydrating dried yeast, that isn't to say someone else could tell the difference...

 

[danestead]

You could be doing more damage by rehydrating at the wrong temp.

I do understand where you are coming from however according to the graph a few pages back, in all cases at a certain temperature, the rehydration in water method resulted in more viable yeast, about 100% more viable yeast at that, as compared to the rehydration in a starter solution as I think the gravity of that would more likely reflect a standard 1.050ish beer than a high gravity, high IBU wort. The only times rehydration in water would be worse off than rehydration in a starter wort or in fact high OG, high IBU wort would be if you rehydrated in very cool water compared to pitching into very warm (30ish degrees) wort (rehydration in starter). Most advanced brewers would be very particular about what temperature they pitch their yeast at, so I find it very unlikely that they would be pitching in the high 20s to low 30s so in my opinion, dry yeast rehydrated in water of almost any reasonable temperature is going to result in more viable yeast.

Would you still agree with your above statement?

 

[Moad]

I was paraphrasing the study I linked to, not really my personal opinion.

"Specifically, incom-plete rehydration, or rehydration at a sub-optimal tem-perature, is likely to result in impaired viability"

You do make a good point and it would be more valid if that graph had a source or some scientific justification to back it up. Again, not saying it is wrong but the article I referenced at least appears to be based on science (even if it was financed by Lallemand).


More from the linked article:

"The temperature of rehydration is believed to be particularly important in avoiding structural damage as a result of phase transition events (characterised by a loss of fluidity) within the plasma membrane. Such events may be avoided by rehydration at a temperature above the phase transition temperature of the cell membrane, which may lead to improved viability in certain yeast strains. However, thermal tolerance in yeast is also known to be strain dependent and determined by factors such as the presence of protectants and synthesis of heat shock proteins"

More variables once again - strain dependant.

I don't think there will ever be a one size fits all answer to the age old question. Strain, rehydration temp, yeast age, OG, wort compostion are a few of many variables that might make sprinkling or rehydrating a better option in any given situation.

 

[MHB]

The recommended pitching rates are an equation that includes wort gravity and is a range of values
For ale typically its somewhere around 0.5-1Million cells per mL per point of Plato
For lager typicalli1-1.5 million cells per mL per point of Plato

For a 23L Ale wort at 1.050 (12.5oP). 23Exp3 * 12.5 * 0.5Exp6 = 143,750,000,000 1.4375Exp11 (at 0.5mil) to 287,500,000,000 or 2.875Exp11
If Dry yeast contains 20 Billion 20,000,000,000 (2Exp10) at 100%, an 11g pitch gives 2.2Exp11
It would take a braver brewer than me to assume that you are going to get 100% viability under any circumstances, but clearly if your yeast is fresh, well looked after and according to most reports carefully and properly hydrated it represents a pretty reasonable pitch. Even dry pitched at say 45% viability gives 9.9exp10 (pretty close to 1Exp11) so a serviceable pitch if not quite ideal

Mark

 

[Ducatiboy stu]

Maybe there is a danger of overpitching yeast if you hydrate it to the letter of the law.......

Maybe a kitten could consume some of the excess yeast cells .....

 

[danestead]

The recommended pitching rates are an equation that includes wort gravity and is a range of values
For ale typically its somewhere around 0.5-1Million cells per mL per point of Plato
For lager typicalli1-1.5 million cells per mL per point of Plato

For a 23L Ale wort at 1.050 (12.5oP). 23Exp3 * 12.5 * 0.5Exp6 = 143,750,000,000 1.4375Exp11 (at 0.5mil) to 287,500,000,000 or 2.875Exp11
If Dry yeast contains 20 Billion 20,000,000,000 (2Exp10) at 100%, an 11g pitch gives 2.2Exp11
It would take a braver brewer than me to assume that you are going to get 100% viability under any circumstances, but clearly if your yeast is fresh, well looked after and according to most reports carefully and properly hydrated it represents a pretty reasonable pitch. Even dry pitched at say 45% viability gives 9.9exp10 (pretty close to 1Exp11) so a serviceable pitch if not quite ideal

Mark

I used to use dry yeast (US-05 in particular) for brews wanting a clean ale yeast. I got a few comments on score sheets of diacetyl in those beers although I couldn't taste it. My palate was not as developed as it is now though, so it may have been there but in low amounts. Because of the diacetyl comments I switched to liquid yeast only to see if that rid myself of the diacetyl problem at the next round of competitions. It's now about 18 months down the track and to be honest, I can't remember what the comments were in last year's competitions, I'd have to dig them up. I do wonder though, if I was getting an insufficient pitch of dry yeast due to pack viability or rehydration process. As far as I can remember, I did rehydrate according to the Fermentis instructions at 27 deg +- 3 degrees and for the appropriate time (can't remember what that was).

 

[MHB]

When judging and I come across inappropriate Diacetyl in a beer, it is usually from under pitching (or unhealthy, under-aerated, yeast stress!) in many cases there are other signs that the yeast isn't happy but Diacetyl is usually the first sign.

The old saying "we make wort, yeast makes beer" is all too true.
Mark

 

[danestead]

The old saying "we make wort, yeast makes beer" is all too true.
Mark

I agree so much. In the beginning a brewer thinks that yeast is the easy part. You throw it in and beer results. It's not until you've got on top of the other things that you realise yeast is the hardest part of the process, for me anyway.