Diacetyl Rests

[biertourist]

If you have diacetyl in the batch, then you could make a starter with new yeast, decant and pitch it to finish up the diacetyl left over in the batch. I'd warm it up before pitching, though.

THIS! -Just did this with the most diacetyl-laden beer I've ever tasted (a zoigl/kellerbier) and making a 3 liter krausen beer / starter and pitching it to the lager at 60F for 2 weeks got rid of an AMAZING amount of diactyl (it was completely clean after 2 weeks).


Adam

[biertourist]

There were a couple of things that appear to have gotten a bit confused in the middle of the thread here.

Big breweries check for both diacetyl and it's precursor (acetolactate); diacetyl and it's precursors are a part of a family together referred to as "vicinal diketones"; the test in use in big breweries is commonly referred to as a "VDK test" for this reason. -So although you can test for both diacetyl and acetolactate, you can only TASTE diacetyl.

The purpose of a diacetyl rest is to increase yeast metabolism so that diacetyl is taken up and converted by the yeast faster than it would be at lower temps.

A related idea is that of the "diacetyl force test" where you take a small bit of your beer and warm it up in the presence of oxygen (and then chill it again because warm beer just tastes bad) so that you quickly convert acetolactate to diacetyl so that you can taste it's presence. The diacetyl force test is used by home breweries and small microbreweries that can't afford the equipment necessary to perform a VDK test and it just enables you to use your tongue as your VDK testing instrument.



Most of the diacetyl is created during yeast's reproductive phase so underpitching can result in larger quantities of diacetyl that will take longer to reduce later (I've also heard it said that pitching warmer can make this more of a problem but I don't have any evidence on that one either way.); certain yeast strains are more likely to produce more diacetyl and less likely to reduce diacetyl quickly than others and you will generally see this in the yeast profile from the mfgr. -Infections of Pediococcus and I believe possibly lacto, too can also produce diacetyl. -Recommending that someone extend a boil to prevent diacetyl makes 0 sense as the process is unrelated to the malt itself; it seems that a few people confuse DMS, which can be driven off with extended boiling, with diacetyl from time-to-time...

You can proactively prevent the formation of diacetyl if you add 2-3 drops of "Biomat DAR" per 5 gallon batch at the same time you pitch your yeast. This product includes a selective enzyme that will quickly convert any acetolactate directly to acetoin, which will prevent the formation of diacetyl. (Normally the acetolactate will get slowly converted to diacetyl and then yeast have to convert that diacetyl to acetoin; this enzyme causes the process to jump straight from acetolactate to acetion without having to wait on the formation of diacetyl or conversion by the yeast's own enzymes.)

-This is starting to introduce some mega lager brewing techniques at the home brewer level, per earlier discussions.
When a bottle costs $5.49 and you only need 2-3 drops per 5 gallon batch, this addition become very cheap "brewing insurance" for the impatient lager brewer.
http://www.midwestsupplies.com/biomat-d ... me=Skimbit

-If you plan on brewing a number of lagers back to back to back this is a very worthwhile investment, IMHO.

Spider nailed it when he said "diacetyl is a problem for impatient brewers". Other common causes are underpitching, transferring yeast off of the beer too soon (or filtering or crash cooling too soon in brew pubs/micros), or bacterial infection.


Adam

[biertourist]

Some British brewers have also noted that some snobby American beer enthusiasts (and newly minted BJCP judges) have tended to cry wolf (well technically they're crying "diacetyl") any time they encounter ANY buttery/butteryscotch-like flavors in a beer. Some UK brewers have even had to abandon using Scottish Golden Promise malt because Americans have voted down their beers on public rating sites stating that they have diacetyl despite the brewery performing a proper VDK test and verifying that the beer contains NO diacetyl and NO diacetyl precursors.

-Bamberg, Germany infamous for its witch hunts (Yep, Bambergers are famous for liking to smoke EVERYTHING from cheese to beer to witches!) and Ratebeer and BeerAdvocate are becoming infamous for their beer "flaw hunts".

Use Golden Promise? Lots of caramely crystal malts or even a long boil? -Be prepared to have a beer snob declare that your beer has diacetyl; VDK testing procedures are a good idea to have ready to confront the myth. (Maybe a beer culture overly focused on identifying faults in beers isn't such a good idea.... *Cough BJCP *Cough)


$0.02 -Keep the Change,
Adam

[Ozwald]

That's one of the reasons I never look at those rate beer sites. Somebody's always got an agenda, everyone's palette is different as well as their preferences. If I see it, I try it, I decide for myself. True, I've drank a ton shitty beer, but I've also enjoyed some pretty good beers that got poor ratings. It's always better to be a beer geek than a beer snob. Especially a beer snob who's listening to other beer snobs who don't know what the hell they're talking about... or what they're tasting, for that matter.