I just racked the remainder of my rye-wheat Hey Jude Celebration Ale into a few commemorative bottles (yes, I kegged the remainder) and I noticed something strange…the beer had a hint of butter flavor to it. Oh my gosh…I’ve got diacetyl in my beer! where did that come from? I never had it before. Is it supposed to be present in this beer style (which I’ve never made before)? Or did I do something wrong? Will other people notice it? Could it harm my unborn grandchild? Should I dump it all and start over? Hmmm… I’ve got some research to do. I do know this from my on-line investigating. Here goes:
Three pathways lead to the creation of diacetyl. The first is through normal yeast metabolism. Brewer’s yeast form a precursor called alpha acetolactate (AAL), which is tasteless. This compound is converted to diacetyl as the beer ages. The reaction that changes AAL to diacetyl is accelerated by high temperature. At cool temperatures it will still occur, but more slowly.Modern brewing practice dictates that beer be aged on live yeast until the vast majority of AAL is converted into diacetyl. Brewer’s yeast, while unable to metabolize AAL, will readily absorb and break down diacetyl into relatively flavorless compounds. By giving the beer enough contact time with the active yeast, the brewer can eliminate the diacetyl. It generally takes only about two weeks of aging ale to assure that it will have no buttery flavors. OKAY. I GAVE IT TWO WEEKS, SO I SHOULD BE GOOD HERE.
Diacetyl is also formed by mutant yeast. Brewer’s yeast that has lost its ability to properly utilize oxygen are called respiratory mutants, or petite mutants (because they form abnormally small colonies on laboratory plates). These yeast are also unable to properly metabolize diacetyl, thus leaving it in the beer. DON’T KNOW ABOUT THIS, BUT I DID BUY MY USUAL PACKAGED YEAST.
A bacteria called pediococcus can also form high levels of diacetyl in beer. While this bug cannot hurt humans, it can make beer sour as well as buttery. Tartness is desirable in Lambic beers, but it is most unwelcome in most other beer styles. The vast majority of brewers do their best to avoid pediococcus! I DON’T THINK THEY HAVE THIS IN LOUISIANA.
By the way - my Irish Red yeast made a bubble gum smell while fermenting. This could be interesting.
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3 comments:
Odd. assuming your sanitation is in order, I wonder if the two weeks was enough or if you had some kind of yeast issue. did you do a gravity reading after primary fermentation?
Science at it's best...I have a new lesson in mind!!! Truly awesome!
Here's some really exciting news - I just got a new book on yeast! Hundreds of pages on nothing but brewer's yeast. I told Barbara it could change my life. Stay tuned for details on diacetyls, aldehydes, esters, enzymes, cell wall structure and permeability, mitochondria, etc.
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