Can Someone Tell Me What A Diacetyl Rest Is For?

[grinder]

G'day brewers.
Maybe I have not read enough but I have been reading recipes from brewers explaining that after primary fermentation (eg, lager) temperature is increased periodically for a "diacetyl rest".
I would just like to know what this means and what is its purpose??
Any info is appreciated
Cheers

 

[bugwan]

Hey grinder,

A diacetyl rest is recommended for lagers. It reduces the diacetyl compounds (created by yeast) that can build up at lower fermentation temps. Diacetyl is an undesirable characteristic in lagers and imparts a buttery flavour.

Fermentation temps for lagers are around 4-8 degrees and diacetyl rest is best around 17-19 for a couple of days. Bring the temps up slowly - over a 24 hour period or so... The same yeast break down the compounds they earlier created.

edit - added a couple of details.

 

[johnno]

G'day brewers.
Maybe I have not read enough but I have been reading recipes from brewers explaining that after primary fermentation (eg, lager) temperature is increased periodically for a "diacetyl rest".
I would just like to know what this means and what is its purpose??
Any info is appreciated
Cheers

Hi Grinder,
Google is your friend.

http://beerme.com/diacetyl.shtml

Plenty of info out there if you do a search.

cheers
johnno

 

[///]

Diacetyl is an undesirable characteristic in lagers and imparts a buttery flavour.

Bah you must work for CUB - me love it in lagers and so does most of the brewers from Czech republic!

The yeast produces diacetyl on its way thru fermentation, with the warming up of the rough beer and the lack of carbohydrates from the finish f fermentation the hungry yeasties have nothing else to accept on the end of thier mission but to re-absorb the diacetyl (DVK) compounds.

Aussie Pro brewers in the big shops hate it. Budvar has a minimum (not maximum) level and is the biggest thing missing from HB examples of the style.

Easy way to produce excess diacetyl is to underpitch and over oxygenate. Easy way to manage is to get tp 1-2 points off your terminal gravity, kill the cooling and let the beer rise to ambient for 2-4days.

YEasts like 34/70 or 2124 produce little, wyeast 2000/2001 produces a motza of it!

Scotty

 

[Zwickel]

let me say that a diacethyl rest is basically not necessary if you pitch the yeast at its working temperature.

For Lagers or Pilseners you should take at least the amount of 1% of the batchsize stiff yeast.
Most of homebrewers have difficulties to get that huge amount of yeast.
Thats why they pitch the yeast already at higher temp to force growing up the yeast.
At that stage, the yeast produces too much diacetyl to be metabolized til the end of fermentation.

That for its recommended at the End of fermentation to increase the temp for about two days to ~14-16C to boost the yeast activity, so it can metabolize the unwanted diacetyl.

edit: Link: http://www.howtobrew.com/section1/chapter10-4.html

 

[bugwan]

Bah you must work for CUB - me love it in lagers and so does most of the brewers from Czech republic!

Scotty

I'll have you, for such a suggestion...!

I was just offering the general reasoning behind diacetyl rests. You and Zwickel explained it better than I - it's basically to get rid of excess diacetyl, rather than all of it.

 

[lonte]

let me say that a diacethyl rest is basically not necessary if you pitch the yeast at its working temperature.

While I always do a simple diacetyl rest as described above in this thread, my reading also suggests that a long laagering time will achieve the same result. So, a diacetyl rest will allow you to get away with a shorter laager, while a long laager time will have the yeast continue to work away at all compounds in the beer, diacetyl included.

 

[razz]

While I always do a simple diacetyl rest as described above in this thread, my reading also suggests that a long laagering time will achieve the same result. So, a diacetyl rest will allow you to get away with a shorter laager, while a long laager time will have the yeast continue to work away at all compounds in the beer, diacetyl included.

I agree wholeheartedly with Lonte on this. I made a Helles last year, after 2 weeks in the keg it was shite (diacetyl) After 8-10 weeks it was very nice.

 

[Jazzafish]

Or you could do what alot of pro brewers do and pick a yeast that doesn't produce alot of diacetyl?

But that just wouldn't be as much fun!

 

[DJR]

Or you could do what alot of pro brewers do and pick a yeast that doesn't produce alot of diacetyl?

Or add Maturex L enzyme to it to metabolise all the alpha-acetolactate into acetoin without the yeast touching it. 10 day process time from start of fermentation to bottling.

Anyone want a 5L drum for a couple of hundred bucks per litre + GST?

http://www.novozymes.com/en/MainStructure/...ration/Maturex/

 

[///]

I'll have you, for such a suggestion...!

just lucky i had the Joke-Lock key on ;-p

Unfrotunately it is treated with extreme concern locally, unfortunately so...

 

[DrewCarey82]

Hi Grinder,
Google is your friend.

http://beerme.com/diacetyl.shtml

Plenty of info out there if you do a search.

cheers
johnno

AHB was designed for the specific purpose of brewers asking questions of other brewers and getting oppinions from other brewers.

 

[Zwickel]

While I always do a simple diacetyl rest as described above in this thread, my reading also suggests that a long laagering time will achieve the same result. So, a diacetyl rest will allow you to get away with a shorter laager, while a long laager time will have the yeast continue to work away at all compounds in the beer, diacetyl included.

basically I agree with that, but if....
your starter got produced at high temp already to force growing,
your starter hasnt contained enough yeast cells so you had to pitch at high temp as well,

in that case, there might be too much diacetyl produced to get metabolized afterwards.

Anyway, a long time lagering period is the best way to cure many fermentation flaws.

 

[marky_mark]

Hey ///,

Is that a fact that the czech beers consider diacetyl a flavour attribute desirable in the beer? What does BJCP think about this in its style guidlines on Bohemian Pilsners.

Perhaps thats what is missing from my bo pils to give it that 'Urquellesque' edge that I've been searching for...

Anyone have some more thoughts?

Mark

 

[marky_mark]

BJCP Bohemian Pilsner Style Discription...

"Rich with complex malt and a spicy, floral Saaz hop bouquet. Some diacetyl is acceptable, but need not be present. Otherwise clean, with no fruity esters."

Guess that answers part of the question... but how much is too much. I've always identified diacetyl as a rancid, off butter kind of taste, but that maybe a combination of oxidation and diacetyl, as I test for it during fermentation by heating a sample and leaving it in the room to form diacetyl from the precursors.

Mark

 

[Adamt]

An acceptable level would create a subtle smooth, buttery feeling on the throat with a minor flavour, certainly I myself wouldn't want a dominantly diacetyl-flavoured beer.

 

[grinder]

basically I agree with that, but if....
your starter got produced at high temp already to force growing,
your starter hasnt contained enough yeast cells so you had to pitch at high temp as well,

in that case, there might be too much diacetyl produced to get metabolized afterwards.

Anyway, a long time lagering period is the best way to cure many fermentation flaws.

Ok
I fermented my pilsener clone with wyeast 2001 for 2 weeks at 10 deg C. I did not do a diacetyl rest and I've got to say that it has no buttery flavour at all. How is this so? Is this rest absolutely neccessary?
I pitched the yeast at a high 25 deg C also before bringing the temp down.
Cheers

 

[lonte]

Ok
I fermented my pilsener clone with wyeast 2001 for 2 weeks at 10 deg C. I did not do a diacetyl rest and I've got to say that it has no buttery flavour at all. How is this so? Is this rest absolutely neccessary?
I pitched the yeast at a high 25 deg C also before bringing the temp down.
Cheers

Have you tasted diacetyl before? Some people (not sure of a percentage) are unable to detect it. Just a thought.

 

[Zwickel]

I pitched the yeast at a high 25 deg C also before bringing the temp down.

as John Palmer said, some yeast strains produce more of diacetyl, than others.
It very depends on the yeast strain.

Cheers

 

[JoePolvino]

I think a d-rest is a good idea even if you don't detect any as fermentation completes. From personal experience, I made an oktoberfest lager without a diacetyl rest, and it ended up having a distinct butterscotch taste. It pretty much ruined a lager that was destined to be a crowd-pleaser.

So just for "insurance" purposes, it is a good idea to do one regardless.

-joe