Diacetyl and the d-rest

[Twostage]

Well I've tasted a few of your beers and they've all been well made ;-)

Apparently a good way to check for diacetyl is to do a "forced test": decant some of the beer and stand it in hot (60ºc) water for 15-30 mins to speed up the oxidation.
Then if it's there you'll really smell it.

Or stick it in the microwave for 15 seconds.

 

[NIGHTSKY BREWING]

Thanks for this TETB, it's really interesting.

This explains why I had to throw down the sink two batches of rye IPA, because I underpitched US-05. I'm guessing the growth phase made it work harder than usual, causing in my case, an oil slick lol

just used US. 05 from 1 packet.....[.0.9litre first then kicked up one more 0.9 starter]...... made a 1.8 litre starter for my last 6% red ale..... look after your yeast and they will look after you.

 

[The-Engineer-That-Brews]

Level of ester production is mostly related to the amount of yeast growth. The usual 1-2 litre starter will not actually have enough cells to ferment a 23 litre batch, so it'll still require growth and you still get esters.

Luckily it's very hard to overpitch yeast. The only time you're likely to do it is when reusing a large portion of a yeast cake for a moderate strength beer. In that case you don't get much, if any growth, so end up with a much reduced fermentation character.

Something I’ve been wondering about JB, is how the yeast ‘knows’ whether it needs to do any growing?

 

[hoppyscotty]

Something I’ve been wondering about JB, is how the yeast ‘knows’ whether it needs to do any growing?

I suspect the yeast will grow as long as there is available food.

 

[Sadfield]

There's sometimes appears a misconception that yeast grow, then ferment. That's all fermentation is, yeast growth under the right conditions, a survival mechanism. It doesn't know it's making a beverage.

https://byo.com/article/fermentation-time-line/

 

[The-Engineer-That-Brews]

@hoppyscotty @Sadfield I should clarify. I frequently read that yeast operates in four states: adaptation; exponential growth (reproduction); stationary and hibernation (I'm paraphrasing because I can't remember the exact terminology).

I think I've heard that reproduction is largely confined to the period when oxygen is available - presumably because aerobic metabolism is so much more efficient; and that relatively few nutrients are consumed during this phase.
Also in the White Labs post they say that various processes (e.g. the production of Diacetyl precursor) only occur during the exponential growth phase.

I've been trying to relate those points to the arguments for and against under/over-pitching, which sometimes talk about "reducing the amount of growth necessary".

Maybe it's a difference of interpretation. Perhaps by 'growth' they are talking about some part of the yeast lifecycle that is different to the exponential growth phase (budding maybe?)

The main argument seems to be that by pitching a large quantity of (healthy) yeast, the cells end up going through fewer generations before using up all the available nutrients before dying or sporifying - without exhausting the lipid reserves that they must share with their daughter cells.

All a bit confusing.

 

[Lunesdale Brewer]

I've brewed all grain beer for 40 years and had never come across the diacetyl issue.
After retiring from work I have re-equipped and reviewed my procedures; in the process I first came across the "problem" of Diacetyl and was surprised by the level of anxiety it generated among home brewers.
I brew Ales at 20 deg C and allow time after final gravity is reached for the yeast to drop naturally and clear enough for transferring to King Keg or bottles.
The beer is then conditioned naturally in its final container - what we tend to call secondary fermentation but is effectively a continuation of the primary fermentation. I guess that provides the conditions required for the diacetyl rest or clean up phase.
Alternatively perhaps I am genetically incapable of detecting it (but I can certainly taste butterscotch or popcorn if I eat it), or I think it is part of the taste profile of Ales and like it?

I realise that the process of brewing lager, cold crashing and forced carbonation in corny kegs is different to that described above and requires more attention to diacetyl removal to meet the strict taste guidelines of modern light lagers.
Some Bohemian style lagers are reported to include traces of diacetyl in their intended flavour profile; perhaps that's why I like them!



Here is a link to an interesting Brulosophy taste test for diacetyl:

https://brulosophy.com/2017/01/02/off-flavor-series-pt-2-diacetyl-exbeeriment-results/
Attached is the George Fix article cited in the Discussion

Are we worrying too much about this?

 

[Sadfield]

@The-Engineer-That-Brews I think exponential just refers to the rate of increase in cells

Are there many arguments for under or over pitching? Both carry undesirable outcomes.

From Wyeast.

A low pitch rate can lead to:

• Excess levels of diacetyl
• Greater levels of diacetyl and 2,3 pentanedione (VDK component)
• Increase in higher/fusel alcohol formation
• Increase in ester formation
• Increase in volatile sulfur compounds
• High terminal gravities
• Stuck fermentations
• Increased risk of infection
• Intensifies or accentuates hoppy aroma

High pitch rates can lead to:

• Very low ester production
• Very fast fermentations
• Thin or lacking body/mouthfeel
• Autolysis (Yeasty flavors due to lysing of cells)
• Low yeast viability
• Low IBU levels
• Greater alcohol yield
• Higher yeast cell count
• Higher percentage of old
• cells in harvested slurry

 

[Twostage]

I've brewed all grain beer for 40 years and had never come across the diacetyl issue.
After retiring from work I have re-equipped and reviewed my procedures; in the process I first came across the "problem" of Diacetyl and was surprised by the level of anxiety it generated among home brewers.
I brew Ales at 20 deg C and allow time after final gravity is reached for the yeast to drop naturally and clear enough for transferring to King Keg or bottles.
The beer is then conditioned naturally in its final container - what we tend to call secondary fermentation but is effectively a continuation of the primary fermentation. I guess that provides the conditions required for the diacetyl rest or clean up phase.
Alternatively perhaps I am genetically incapable of detecting it (but I can certainly taste butterscotch or popcorn if I eat it), or I think it is part of the taste profile of Ales and like it?

I realise that the process of brewing lager, cold crashing and forced carbonation in corny kegs is different to that described above and requires more attention to diacetyl removal to meet the strict taste guidelines of modern light lagers.
Some Bohemian style lagers are reported to include traces of diacetyl in their intended flavour profile; perhaps that's why I like them!



Here is a link to an interesting Brulosophy taste test for diacetyl:

https://brulosophy.com/2017/01/02/off-flavor-series-pt-2-diacetyl-exbeeriment-results/
Attached is the George Fix article cited in the Discussion

Are we worrying too much about this?

In my early days of brewing I accidentally pushed the wort to 24 (by the misuse of a fish tank heater ) and it ended up tasting really butterscotch but I liked it. It did give me a bit of a rough head the next morning though .

 

[hoppyscotty]

I've read that in Czech lagers they do like a bit of diacetyl and deliberately brew it into the beer. I've never really picked up on it myself, maybe it's really subtle and I'm not super sensitive to that flavour, but ultimately it's only an off flavour if it's not intended. Look at the banana ester synonymous with Belgium beers...in any other style that is an off flavour...so even if you do brew a beer with some diacetyl then just 're-market' it as a different beer and pretend its a flavour component you were shooting for all along Brewing a lager and get some banana esters to it...call it a Saison! Brewing an Ale and get hints of dactyl...call it a 'Czech Ale'...nobody will be any the wiser!

 

[JockyBrewer]

There's some diacetyl in Pilsner Urquell (which I liked until someone pointed it out to me, and now I can't taste anything else!), and quite a lot in some of the other Czech lagers I've had too. Budvar is clean though.

 

[Alan_Reginato]

I think there's a little confusion involving DMS and diacetyl here.

 

[MashBag]

although sometimes I worry that a badly made starter just contributes a lot of very tired yeast.

Worse than sprinkling.

 

[RoomWithABrew]

ALDC enzyme handy, 0.5 ml per 23 litre batch. Costs 20 p per batch, seems like a bargain insurance policy on top of a little temp bump.
Although I pitch plenty, do a D ramp and use the enzyme.
So belt, braces and a safety pin.