What is Diacetyl?

I read in last month's Brew Magazine about common issues with excessive diacetyl. They never stated what it was or what taste issues it causes?

It is a yest by-product, usually in lager yeasts, that gives a buttery or butterscotch flavor. Usually, it is not a problem if you keep it on the yeast long enough, and handle the yeast well (proper pitching rate and temp), and may never even be present. If you do detect it, a diacetyl rest will usually take care of the problem, that is letting the temp rise to the 60s for lagers and 70s for ales, at the tail end of fermentation. Taste you hydrometer samples for diacetyl, if you detect butter or butterscotch, do a D-rest, but I have never had a problem with it, and some people can't even taste it in the amounts that may be present in beer.

Thanks, I was just curious what it was.

Diacetyl
Diacetyl is most often described as a butter or butterscotch flavor. Smell an unpopped bag of butter flavor microwave popcorn for a good example. It is desired to a degree in many ales, but in some styles (mainly lagers) and circumstances it is unwanted and may even take on rancid overtones. Diacetyl can be the result of the normal fermentation process or the result of a bacterial infection. Diacetyl is produced early in the fermentation cycle by the yeast and is gradually reassimilated towards the end of the fermentation. A brew that experiences a long lag time due to weak yeast or insufficient aeration will produce a lot of diacetyl before the main fermentation begins. In this case there is often more diacetyl than the yeast can consume at the end of fermentation and it can dominate the flavor of the beer.

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How to Brew - By John Palmer - Common Off-Flavors

...wrong forum btw

I realized that after I posted and reposted in the right forum. Thanks

OSHA is seeking comments regards a proposed rule on Diacetyl. See below for details:

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DEPARTMENT OF LABOR

Occupational Safety and Health Administration

29 CFR Part 1910

[Docket No. OSHA-2008-0046]

RIN 1218-AC33

Occupational Exposure to Diacetyl and Food Flavorings Containing Diacetyl

AGENCY: Occupational Safety and Health Administration (OSHA), Department of Labor.

ACTION: Advance notice of proposed rulemaking.

SUMMARY: OSHA is requesting data, information, and comment on issues related to occupational exposure to diacetyl and food flavorings containing diacetyl, including current employee exposures to diacetyl; the relationship between exposure to diacetyl and the development of adverse health effects; exposure assessment and monitoring methods; exposure control methods; employee training; medical surveillance for adverse health effects related to diacetyl exposure; and other pertinent subjects. In this notice, OSHA intends the term "diacetyl and food flavorings containing diacetyl" to encompass other constituents of food flavorings containing diacetyl. In addition to information on diacetyl, OSHA seeks information on acetoin, acetaldehyde, acetic acid, furfural, and other compounds present in food flavorings that may cause or contribute to flavoring-related lung disease. The Agency is also interested in and seeks information about diacetyl present in substances other than food flavorings (e.g., naturally occurring diacetyl or diacetyl in fragrances) as well as substitutes used in place of diacetyl (e.g., diacetyl trimer). The information received in response to this document will assist the Agency in developing a proposed standard addressing occupational exposure to diacetyl and food flavorings containing diacetyl.

DATES: Comments must be submitted (postmarked, sent, or received) by April 21, 2009.

ADDRESSES: You may submit comments, identified by Docket No. OSHA-2008-0046, by any of the following methods:

Electronically: You may submit comments and attachments electronically at redirect, which is the Federal eRulemaking Portal. Follow the instructions online for submitting comments.

Fax: If your comments, including attachments, do not exceed 10 pages, you may fax them to the OSHA Docket Office at 202-693-1648.

Mail, hand delivery, express mail, messenger or courier service: You must submit three copies of your comments and attachments to the OSHA Docket Office, Docket No. OSHA-2008-0046, Room N-2625, U.S. Department of Labor, 200 Constitution Avenue, NW., Washington, DC 20210; telephone 202-693-2350 (TTY number 877-889-5627). Deliveries (hand, express mail, messenger or courier service) are accepted during the Department of Labor's and Docket Office's normal business hours, 8:15 a.m.-4:45 p.m., e.t.

Instructions: All submissions must include the Agency name and the OSHA docket number (Docket No. OSHA-2008-0046). Because of security-related procedures, submissions by regular mail may result in significant delay in their receipt. Please contact the OSHA Docket Office at the above address for information about security procedures for submitting comments by hand delivery, express delivery, and messenger or courier service.

All comments, including any personal information you provide, are placed in the public docket without change and may be made available online at redirect. Therefore, OSHA cautions you about submitting certain personal information, such as social security numbers and birthdates. For further information on submitting comments, see the "Public Participation" heading in the SUPPLEMENTARY INFORMATION section of this document.

Taken from CyberRegs

I had it BAD in an Amber Lager. That batch had a nice D rest, too.

I am pretty sure it was caused by contamination. It developed in the keg.

I made an ale starter and pitched it in the keg. Let it sit for three weeks at room temperature and 90% of the butter smell and taste was gone. That keg is just about to kick, now.

This is a great thread on the simplest cure for it....

https://www.homebrewtalk.com/f13/preventing-diacetyl-hold-butter-please-70438/

I don't want to beat a dead horse here, but if my ales are fermenting close to 60°F I won't be likely to develop diacetyl, right? My house is pretty cold and my water bath usually hovers a shade over 60 and I've never tasted diacetyl over the past year that I've been brewing (either that or I have and don't know what it tastes like).

BigJay13 said:

I don't want to beat a dead horse here, but if my ales are fermenting close to 60°F I won't be likely to develop diacetyl, right? My house is pretty cold and my water bath usually hovers a shade over 60 and I've never tasted diacetyl over the past year that I've been brewing (either that or I have and don't know what it tastes like).

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Diacetyl tends to be more of an issue for Lagers than Ales.

Lager yeasts work better at cooler temperatures. If you pitch your yeast into a lager too warm, you tend to get more diacetyl. Then, when you bring the wort down to the proper fermentation temperature, the yeast (which is working slower due to the cooler temps) does not process all the diacetyl. The "Diacetyl Rest" is supposed to allow the now warmed up and harder working yeast to eat up the excess diacetyl.

Since ale yeasts work at warmer temperatures, they tend to eat the excess diacetyl in the course of normal fermentation. In some ales, a little diacetyl is considered part of the character.

You know the really strong butter smell you get when you open a bag of microwave buttered popcorn? THAT is diacetyl.

BigJay13 said:

I don't want to beat a dead horse here, but if my ales are fermenting close to 60°F I won't be likely to develop diacetyl, right? My house is pretty cold and my water bath usually hovers a shade over 60 and I've never tasted diacetyl over the past year that I've been brewing (either that or I have and don't know what it tastes like).

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With the exception of a few strains, you have to work pretty hard to get diacetyl in an ale period.

BigJay13 said:

I don't want to beat a dead horse here, but if my ales are fermenting close to 60°F I won't be likely to develop diacetyl, right? My house is pretty cold and my water bath usually hovers a shade over 60 and I've never tasted diacetyl over the past year that I've been brewing (either that or I have and don't know what it tastes like).

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Diacetyl is present in the fermentation of BOTH ales an lagers, it is an ISSUE more in Lagers, because it can be picked up more easily, and a good commercial lager brewery wants to make a consistant product, that is why they take care to eliminate any possibility of off flavors.

In some ales a bit of it is actually a plus...

But if it weren't possible in all types of fermetnations, the presence of it or lack of it wouldn't be brought up in the BJCP style guides or in judging for just about every style....

There's a good article here..

"THE ROLE OF DIACETYL IN BEER
By Moritz Kallmeyer"

The Abstract begins...

Diacetyl as a product of fermentation is more characteristic of ales than lagers. Diacetyl is produced early in the fermentation, and then most of it is reabsorbed by the yeast and reduced to flavourless compounds later on. Yeast strains differ markedly in their diacetyl reduction ability. Some ales and a few lagers (such as the famous Pilsner Urquell) contain perceptible amounts of diacetyl, but as a rule modern brewers consider it as a fault. This is because certain bacterial infections and other errors in brewing technique will increase diacetyl levels resulting in unacceptable beer aroma and flavour profile. This parameter thus serves as a quality check. However, it is important to remember that diacetyl flavour is a natural by-product of yeast fermentation, and in some beer styles it is an optional or even required flavour component in low amounts.

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From here....


Drayman's Brewery and Distillery

There's another good one on the topic here...

BT - Diacetyl: Formation, Reduction, and Control


But like Biermuncher's thread, even an ale can benefit for a bit of a rest to let it clean up.


There's two methods of rests listed in the Kallmeyer article...one for ales and warmer beers....interesting.

Maturation of beer flavour requires the presence of yeast as a catalyst. There are many methods of finishing that have the sole objective of prolonging the contact of beer with yeast after primary fermentation is completed. I want to emphasize that a diacetyl rest with most of the yeast lying at the bottom of the tank and not enough in suspension is of no use. Most lager breweries, especially those that use Weinhenstephan 308 or similar “diacetyl producing yeast’s” employ a long diacetyl rest, in order to minimize diacetyl in the finished beer.

Method 1
If a very cold primary fermentation was used it involves allowing the beer temperature to rise from the controlled primary fermentation temperature of about 10°C to 15-18°C when the primary fermentation is coming to an end. Normally, the time is determined by the attenuation of the beer. If, for example the wort starting gravity was 1050 and the expected terminal gravity is 1010, then the diacetyl rest would be commenced when the beer has attenuated to about SG 1023 when two-thirds of the total fermentable material in the wort has been consumed. The diacetyl rest normally lasts for 48-72 hours, until primary fermentation is over and secondary fermentation is under way. At this time the temperature is lowered when the more traditional method is followed, probably 1°C per day until the lagering temperature of 0-1°C is reached.

Method 2
If a warmer primary fermentation temperature was used for ale or lager the diacetyl rest involves either lowering the beer temperature 2 or 3°C at the end of primary fermentation or keeping it constant for up to 6 days. In lager yeast strains with low diacetyl production it is common practise nowadays to employ a short diacetyl rest followed by centrifuging to remove excess yeast and then crash cooling to 0°C. When brewing ales, that should have very low diacetyl levels especially German Ales like Alt and Kölsch, the implications are to not use highly flocculent yeast and to allow an extended primary fermentation, albeit at cooler temperatures until sufficiently low diacetyl levels are reached. Yeast that settles in the cone is still removed on a daily basis.

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Interesting for ALES one of the recomendations is to LOWER the temps a bit...or leave them at the same temp for 6 days...learns something new everyday...I'm going to have to try the cool rest.

It also backs up the idea of leaving beers on the yeastcake for awhile longer to allow the yeasts to clean up after themselves.

The easiest thing I've found for diacetyl is simply time. Give the yeast plenty of time to do what they do and none of the complicated temperature rests are needed, ale or lager.

Brewsmith said:

The easiest thing I've found for diacetyl is simply time. Give the yeast plenty of time to do what they do and none of the complicated temperature rests are needed, ale or lager.

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+1 on this!!! That's sort of the point of biermucnher's thread.



The the "cooler rest" sound interesting for ales....

For me, it's more like the "Lazy Rest"

My Pale Ale has sat in primary for three weeks now and I'm okay with it.