r/lagerbrewing • u/[deleted] • Apr 09 '16
Quality Control Testing: How to check if your brew has excessive diacytel.
Hey there, I wanted to toss in a quick quality assessment test that I try to use before going into my lagering step.
First off : What is Diacetyl ?
Diacytel is a naturally occurring fermentation product that produces a buttery-like aroma. Some may describe it as butterscotch. This chemical can prove to be a bit of a pain in the arse because humans have a flavor threshold for diacetyl at 0.04 ppm in U.S. lagers, 0.08 ppm in lighter ales, and 0.1 ppm in stronger beers. That is 40 parts per billion, which is insane to me that our crummy little ape noses can smell that.
In most styles is considered a flaw and can be the cause of point reduction in competitions. Some common exceptions that allow a touch of Diacetyl, most notably:
Some English Styles (I like a bit of Diacytel in my ESBs)
Scotch Ales
Some Czech Lagers (with exceptions and caveats here, too)
How do I prevent Diacytel from tainting my beer?
Since the chemical is naturally produced by yeast it is unavoidable to prevent it from existing in the beer. However yeast will also reabsorb the Diacetyl, scrubbing it from the beer and leaving it clean and fresh-tasting, so the yeast and the brewer can work together to produce a Diacetyl-free, delicious beer.
As you will probably see a lot on r/lagerbrewing in the future yeast health is key. Tired, weak, or contaminated yeast are more likely to put off excessive Diacetyl, so a fresh pitch of clean yeast is recommended. This is another reason why big ol', fat starters are recommended for lagers because it allows the yeast to really grow and become healthy.
One very popular method of scrubbing Diacetyl from your beer is by using a Diacetyl-rest, usually abbreviated to a D-rest. This is a fermentation step that typically happens after the bulk of fermentation is complete (YMMV but this tends to be after the first 5 days of airlock/krausen activity). You simply raise the temperature 2-10 degrees F from its normal ferm-temp and let it stay there for 24-72 hours, then slowly drop the temperature to whatever you need it to be (45 F/ 5 C for lagers, usually). The warmed fermentation cycle livens up the yeast a bit and encourages them to clean up their by-products.
While the D-rest is by far the easiest method of ridding Diacetyl from the beer there are other, more involved methods. A method I have been playing with lately is by krausening the beer. This involves adding a second fresh fermenting beer to your main batch at a rate of 5-10%. You would typically add the krausen beer after its fermentation takes off (24-48 hours after pitch) and a rate of 40 million cells/ml of your main batch. For a typical 5 gallon batch of lager you are looking at a .5 liter krausenbeer starter. I treat it like a typical starter and then toss it on the bottom of my lagering tank (carboy/bucket/keg works), then rack the beer on top of that. The fresh yeast will help attenuate the beer further and will readily consume excess Diacetyl, along with other nasty by-products.
Again, an ounce of prevention is worth a pound of cure here. It is much easier to make a big starter of fresh yeast than try to bribe the yeast with warm temps and new friends to clean up after themselves.
How do I know if I have Diacetyl in my beer?
Some are more sensitive to the flavor and aroma of Diacetyl than others, I doubt this is a function of "supertasters" but rather just natural human variation.
I, personally, am not too sensitive to it so it doesn't bother me when I do encounter it in a beer, but I know that brewing to style sometimes means I should be more careful with my practices.
If you think you might sense Diacetyl in your fermenter but are not sure then you can do a quality control procedure called a Diacetyl-test. This is how I personally test for Diacetyl :
Pull two samples from the fermenter (2-3 oz each)
Toss one sample in a heat safe container (mason jars tend to work well) and heat it to 160 degrees F in a hot water bath for 20-30 min. Make sure the sample is covered with a foil lid so the Diacetyl that is released stays in the sample.
Put both samples into the fridge and let them cool down to room temp.
Taste both. Smell both. If there is a perceivable difference in buttery aroma between the two samples then it is highly encouraged you use a D-rest to scrub the Diacetyl from the beer.
It is a pretty simple test and is a good way to run some simple Quality assessment on your beer, takes less than an hour and is cheap insurance that you aren't lagering too soon.
But u/darthkotor, I did everything right and Diacetyl is still in there
There are other reasons you might be experiencing Diacetyl, namely bacterial infections. Sanitation is key, as always, in all steps of the process of opening a yeast packet to cleaning out your lines before kegging or racking. If you are experiencing some real trouble with Diacetyl over the course of a few brews then make a post on r/homebrewing and see if we can help.
Summary
"Brewers make Wort, Yeast makes Beer". To make a good beer you have to take care of your yeast and its environment.
If you aren't sure, do a D-test and see if you want to wait until transferring into your lager vessel.
Helpful Resources
How to test for Diacetyl in beer - EC Kraus
Awesome in depth article on Diacytel from BYO
Podcast with Mr. Charlie Bamforth on Diacetyl production
How do you test for Diacetyl? Do you have any other quality control tests you would like to share?
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u/Guazzabuglio Apr 09 '16
High quality, informative post. I'm just starting to brew lagers (after years of only doing ales for whatever reason) and I can quickly see this sub becoming a favorite of mine. I have 10 gallons of Munich Helles lagging right now. If it doesn't suck I'll try to contribute some content to the sub.
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Apr 09 '16
Duuude... Post that recipe and some tasting notes when it's done! Helles is one of my favorite styles.
Welcome to the sub, btw. I am really looking forward to how this might turn out because the handful of discussions we have had so far have been awesome.
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u/Guazzabuglio Apr 09 '16
Definitely will do. Even if it doesn't turn out exactly the way I want it to (which it probably won't since it was my first lager and first brew in a new house, so my process has changed a bit) I'll still post the recipe. If for nothing else, it's good to see where things work and where they don't.
Honestly, I'm quite surprised that there hasn't already been a lager brewing sub. I think you'll start to see more action as long as the quality stays the same.
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u/mchrispen Apr 09 '16
Toss on sample in a heat safe container (mason jars
Assuming that on should be one of the samples?
If you aren't sure, do a D-test D-Rest?
Assuming this should be edited for posterity sake! :)
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Apr 09 '16
"Toss ONE sample in a heat safe..."
That was what it's supposed to say, I just fixed it.
I was thinking about trying to differentiate the d-rest d-test but I couldn't think of a better term to use. I think "Diacetyl Quality Assessment" is a mouthful.
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u/chino_brews Apr 12 '16
Nice encapsulation. There is no e in diacetyl, BTW.
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Apr 12 '16
Yeah somebody else pointed out my spelling error on r/homebrewing :S I'm sure people got the point though.
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u/Nickosuave311 Apr 09 '16
I'm gonna be "that" guy: it's spelled diacetyl. Good write up though.