Diacetyl Rest Temperature and Time?

Jeff, thanks for your input. So, about ¼ of the population is genetically ‘blind’ to diacetyl vs. the value of 1/3 I mentioned in my prior post.

Cheers!

 

That is what I remember, it may be more like the 1 in 5. I can't find a good reference to that.

PTC has about a 1 in 4 blindness to the bitterness it has. This is the classic demo on how our genes determine that we taste differently. Ken Schramm did a demo at the 2010 NHC, and I could taste it - nasty intense bitterness.
http://learn.genetics.utah.edu/content/inheritance/ptc/

 

I think I fall into this category. I have never, that I know of, detected DMS, but can get diacetyl right away. It is possible I have detected DMS but didnt know that's what it was.

 

Did you ever drink Rolling Rock? That beer has lots of DMS (intentionally).

Cheers!

 

Have you ever noticed a creamed corn-like aroma during the boil? (If not, put your nose over the kettle next time and take a long whiff.) It may be masked to some extent by hop aromas, but it's there. That's DMS.

 

That is very, very fascinating - and would validate a lot of what Jack has said anecdotally with regards to influence of pitch rate on fermentation characteristics.

If I can get a link to the article I'll post it up here.

 

I'd like to read that too if someone can find the link. Here's one that says for very high gravity brewing (24oBx wort) that the level of diacetyl in green beer is higher at higher pitch rates...

http://www.ifrj.upm.edu.my/16 (4) 2009/11 IFRJ-2009-112 Nguyen Vietnam 2nd proof.pdf

Interestingly, it also says this:
"In terms of flavor, Erten (2007) found lower diacetyl level at higher pitching rate whereas Verbelen (2008) reported the contradictory result. It is noted that although these results did indicate that high pitching rate is clearly advantageous in high gravity brewing, the initial gravity of all worts in the experiments above was not over 15 – 16
oP."

 

What did Jack say about pitch rate influence on fermentation characteristics?

 

Jack has said that the recommended pitching rates are conservative, and that equivalent or better results can be achieved with a smaller pitch. I think - correct me if I'm mistaken @JackHorzempa...

 

Oh, okay. I thought you meant he had talked about specific pitch rates affecting diacetyl or other characteristics. But as far as talking in general about pitch rates, I have tried to ask Jack several times what he believes is an appropriate pitch rate in terms of cells/volume/gravity, but he has steadfastly declined to answer.

 

I have never noticed it before, I will see if I can smell it when I brew tonight.

 

@utahbeerdude thanks for that link! I would like to read the entire article but even the abstract was informative:

“The volumetric productivity of the beer fermentation process can be increased by using a higher pitching rate (i.e. higher inoculum size). However, the impact of the pitching rate on crucial fermentation and beer quality parameters has never been assessed systematically. In this study, five pitching rates were applied to lab-scale fermentations to investigate its impact on the yeast physiology and beer quality. The fermentation rate increased significantly and the net yeast growth was lowered with increasing pitching rate, without affecting significantly the viability and the vitality of the yeast population. The build-up of unsaturated fatty acids in the initial phase of the fermentation was repressed when higher yeast concentrations were pitched. The expression levels of the genes HSP104 and HSP12 and the concentration of trehalose were higher with increased pitching rates, suggesting a moderate exposure to stress in case of higher cell concentrations. The influence of pitching rate on aroma compound production was rather limited, with the exception of total diacetyl levels, which strongly increased with the pitching rate. These results demonstrate that most aspects of the yeast physiology and flavour balance are not significantly or negatively affected when the pitching rate is changed. However, further research is needed to fully optimise the conditions for brewing beer with high cell density populations.”

Permit me to define what I consider to be the definition of a healthy fermentation:

A relatively quick start of fermentation (signs of fermentation in less than 24 hours and more optimally at less than 12 hours). A quick start to fermentation means that the yeast is creating a hostile environment for other microorganisms that are present in the wort.

No off flavors are perceptible in the finished beer (e.g.. low levels of acetaldehyde, low levels of diacetyl, low levels of fusel oils, etc.).

The beer reaches the intended final gravity (i.e., the fermentation did not stall).

The fermentation completes in a timely manner (e.g., primary fermentation for a moderate gravity ale complete in
less than a week).

I am able to meet all of the above metrics by pitching a yeast cell count significantly less than what is indicated by the ‘results’ of the yeast calculator on the Mr. Malty website.

For completeness I should mention that other aspects need attention for a healthy fermentation to occur like adequate aeration/oxygenation, proper fermentation temperature control and proper nutrition for the yeast (I add Wyeast yeast nutrient to my wort).

Cheers

 

I trust you won't be quoting the part you underlined and bolded in the future out of context, without reading the paper. The synopsis doesn't say much about the experimental conditions, says nothing about evaluation criteria, and doesn't contain any quantitative data.

I believe what you're saying is that pitch rate is unimportant, or not very important. If so, I understand that. I don't agree, but I would agree to disagree. Perhaps when discussing the Mr. Malty calculator, you could say that pitch rate is not very important, rather than attacking the calculator's parameters and assumptions. For someone who doesn't subscribe to a particular pitch rate to say that someone's yeast calculator gives an answer that's too high is akin to a member of the Christian Scientists critiquing a surgeon's technique.

 

“I believe what you're saying is that pitch rate is unimportant”

To the best of my knowledge I have never explicitly stated that pitch rate is unimportant.

One of the necessary conditions for a healthy fermentation is that a sufficient amount of healthy yeast needs to be pitched, I personally pitch a sufficient amount of healthy yeast to my wort.

Cheers!

P.S. I have on more than one occasion mentioned that the pitch rate of 0.75 million cells/ml/P that is utilized in the Mr. Malty yeast calculator is incorrect/conservative since that rate is for reusing yeast vs. using a package of newly purchased liquid yeast.

 

So what's the better rate, or minimum good rate? In your opinion. (The one that you use.)

 

I downloaded the article. BM me if you want a copy

 

Wow. It might also explain why the helles I brewed last spring was a diacetyl bomb despite my having done a d-rest. Mind = blown.

That beer was a disaster, and it's always puzzled me. I didn't do anything significantly different from my normal lager fermentations, other than the fact that I used an unfamiliar yeast, WLP860, their seasonal helles strain. (I usually use WY2124 for just about all my lagers.) Unfortunately that beer tasted so buttery I drain poured most of it, and I figured maybe the problem was the yeast strain--which admittedly seemed unlikely, since White Labs would probably have pulled it off the market if it was that prone to diacetyl production. Now I'm thinking that maybe what happened was that I somehow significantly overpitched for this relatively low gravity lager. I might've even intentionally overpitched to some degree, not knowing what this particular yeast was like and figuring that was the "safe" thing to do. Unfortunately, I don't usually keep records of my starter sizes and pitch rates, so I may not be able to check this. Lesson for today: keep records of that stuff.

 

No need to jump to conclusions here. The author of this paper didn't study the effect of diacetyl rests at higher temps or long term conditioning effect on final diacetyl concentration. Long story short - don't stop making your lager starters just yet...