Anyone actually take the time to do a diacetyl test?

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Rob2010SS

Supporting Member
HBT Supporter
Joined
Jun 16, 2017
Messages
3,401
Reaction score
1,363
Location
Spring Grove
I have a marzen in the tank that I've been slowly ramping up temp on and it hit 68*F yesterday (brewed on 8/30, so 11 days since brew). Fermentation appears to be done based on the tilt readings. My plan was to let it sit at 68F through the weekend for the d-rest, hook up CO2 and crash on Sunday night. I don't do many lagers (this is my 4th). I have never seemed to have an issue with diacetyl as I've never picked up on it and I've never actually performed the test for diacetyl (where you heat up a sample..). I was going to skip the diacetyl test but started wondering if I should do it.

My question is : Does anyone routinely do a diacetyl test or do the majority just let it sit for a few days as that should be sufficient?
 
Every beer. As Denny Conn and Drew Beechum have recommended, the sample can be warmed to 150F in a microwave so pretty easy. Just tested a marzen and it had a definite buttery aroma and flavor.
 
Every beer. As Denny Conn and Drew Beechum have recommended, the sample can be warmed to 150F in a microwave so pretty easy. Just tested a marzen and it had a definite buttery aroma and flavor.

Every beer, or just lagers?

I guess I'm just not sensitive to diacetyl. I think I know what it's supposed to smell/taste like but I never seem to detect it. I finally got tired of having judges ding me on points for having it. So it must be there. Three or four years ago I simply incorporated a D-rest into every lager. It adds 4-5 days to the work flow, but at least the judges seem to like it better.

That said, I don't test. I just let the temperature free-rise into the upper 60s/lower 70s and let the yeast do its thing when the SG approaches +5 points of FG. That's also when I attach a spunding valve set to ~15 psig/1 atm. After a few days at d-rest temperature, I start a slow cool down of 3-4F per day, rather than a hard crash, down to either "conditioning" temperature ( <45F for ales) for 2-3 weeks, or "lagering" temperature (as cold as my glycol system can go without freezing up) for 2-3 months.

The 15 psig at d-rest temps leaves positive pressure in the fermenter during the 'crash' to prevent suck back and results in an appropriate pressure (~11.5-12.5 psig) for the beer at serving temperature in the kegerator. I can't tell if there's diacetyl or not, but nobody else does either, so it must be all good. Maybe I should do the microwave test. What do I look for once I get the sample up to 150F?
 
Last edited:
With hop creep being an ever present issue nowadays I’d recommend most people do one for dry hopped beers if you’re dry hopping at fermentation temps.

See reports of Russian River beers taking 7-9 days sometimes to get below threshold which is crazy.
 
With hop creep being an ever present issue nowadays I’d recommend most people do one for dry hopped beers if you’re dry hopping at fermentation temps.

See reports of Russian River beers taking 7-9 days sometimes to get below threshold which is crazy.
No dry hop on this one.

I think I'll take everyone's advice and do the test. Just need to read up on how to do it as I've never done it.
 
When I judge beer I don't have a microwave ... so no. :)

The reason people do a forced diacetyl test is that even though there may not be detectable diacetyl at the time, there may still be some of its precursor, α‐acetolactate, in the beer, which will be oxidized to diacetyl later. Either a half hour later (at forced test temps) or days/weeks later at lower temps.
 
The reason people do a forced diacetyl test is that even though there may not be detectable diacetyl at the time, there may still be some of its precursor, α‐acetolactate, in the beer, which will be oxidized to diacetyl later. Either a half hour later (at forced test temps) or days/weeks later at lower temps.
Understood - but in my own experience, by the time you get around to bottling a lager you either have it or you won't. I guess there are people who rush things. I am not generally in a rush, so I guess either I'm lucky, or my process lets the yeast do its job.
 
Every beer, or just lagers?

I'm one of those tasters that is sensitive to diacetyl so I test every beer since I'm going to drink most of the 5 gallons I make 😀

It used to be a PITA until I went to a Denny and Drew zoom talk on Simple Brewing in which they told me to just use the microwave. Easy peasy.
 
Is there a good reason not to test? It doesn’t require much time or sample volume. Seems like an easy check. I use the same samples that I take for gravity readings.
 
Okay honestly not being facetious here: Is there some rush I'm not aware of to get a lager (say a Märzen) out of the fermenter that leads to this problem? I guess maybe I'm just the old fart, but I generally give the carboy (or whatever) a couple of twists at the end to 1) help any yeast on the sides to settle to the bottom and 2) to stir up the bottom layer just a bit to help with a diacetyl rest. On big beers like a Doppelbock where my yeast may have been stressed or otherwise not in prime shape, I kräusen to help with "cleanup duties." Since "lager" means "store" I always let the beer finish on the yeast cake for a month or so.

It's entirely possible the world has moved on from my ancient ways. :)

Is there a good reason not to test?
If you are already sampling I can't think of a reason in the world NOT to do a test that's available. I use Tilts so I don't have that last sample.
 
Okay honestly not being facetious here: Is there some rush I'm not aware of to get a lager (say a Märzen) out of the fermenter that leads to this problem? I guess maybe I'm just the old fart, but I generally give the carboy (or whatever) a couple of twists at the end to 1) help any yeast on the sides to settle to the bottom and 2) to stir up the bottom layer just a bit to help with a diacetyl rest. On big beers like a Doppelbock where my yeast may have been stressed or otherwise not in prime shape, I kräusen to help with "cleanup duties." Since "lager" means "store" I always let the beer finish on the yeast cake for a month or so.

It's entirely possible the world has moved on from my ancient ways. :)


If you are already sampling I can't think of a reason in the world NOT to do a test that's available. I use Tilts so I don't have that last sample.

Agree. Take the low/slow route, especially with lagers. Increasingly all my beers "finish" faster these days, 6-8 days for ales, something less than 14 days for lagers. But there's a distinction, at least in my mind, between "finishing" (fermentation) and "done" (ready for kegging/conditioning/lagering). Just because I think it may be completely fermented doesn't mean my FFT accurately predicted Final Gravity. Plus, isn't the d-rest a step to ensure "completion" of the process, by which I mean "in addition to" fermenting to FG?

Over time my processes and protocols have evolved from 'quicker' to 'more patient', even as my time from pitch to FG has seemed to decrease. This evolution seems to have speeded up in the last several years as I switched from glass and plastic fermenters to stainless steel conicals, and from no temperature control to frozen ice bottles and finally glycol chilling. I no longer rack to a secondary fermenter. Instead of removing wort from the lees I dump the lees out the bottom, leaving a nice layer of healthy yeast to spund carbonate and clean up the detritus left behind and in suspension. Later I soft crash and harvest out yeast for future batches, and then cold crash for clarity and conditioning. All of this accomplished without ever opening the lid on the fermenter. It's a lot more leisurely this way, and a lot more civilized (Old Bull, Young Bull). Little to no oxidation, no infections, less cleanup, better beer. Haven't gotten into the routine of testing for diacetyl since I do not seem to sense it and my fermentation profiles for both ales and lagers already include temperature steps to higher than normal fermentation range for several days at or near FG, which accomplishes a d-rest I suppose. Either way the beer tastes good to me.

I see from your avatar that you're from K.C. (Go Chiefs!). Wife and I grew up in Northtown on the Missouri side and both went to K.U. (Go Jayhawks!). Still have some family in the area and get back from time to time to sample some Smokehouse and Jack Stack 'que, and of course some Boulevard beer.
 
isn't the d-rest a step to ensure "completion" of the process, by which I mean "in addition to" fermenting to FG?
I guess that's how I've been rolling for ... 30 years? It "feels like" folks have invented a solution in search of a problem, but I'm always willing to learn. I don't make anyone else's beer so I can't comment on the testing needed. I do judge their beer and certainly have tasted a lot of otherwise good beers ruined by diacetyl. If there's a way to help them avoid that with their process then I guess I'm all for it. The answer to it is always a diacetyl rest so why not just give it another week or two? (or more?)

Wife and I grew up in Northtown on the Missouri side
1600011721240.png
:D

I live near Liberty. Love me some Smokehouse. I mean come on, if those beans aren't the best beans in the world, I don't know what is.
 
S
I guess that's how I've been rolling for ... 30 years? It "feels like" folks have invented a solution in search of a problem, but I'm always willing to learn. I don't make anyone else's beer so I can't comment on the testing needed. I do judge their beer and certainly have tasted a lot of otherwise good beers ruined by diacetyl. If there's a way to help them avoid that with their process then I guess I'm all for it. The answer to it is always a diacetyl rest so why not just give it another week or two? (or more?)


View attachment 698244:D

I live near Liberty. Love me some Smokehouse. I mean come on, if those beans aren't the best beans in the world, I don't know what is.

Small world. I have a sister there who lives off Barry Road (nephew went to Oak Park). Wife has a sister in Liberty and a niece who's a nurse at NKC Hospital, where her father was a doctor and trustee on the Board. We haven't lived there since the early 80s. Things certainly have changed. But the bar-b-que is as good as ever.
 
I do a 3 to 5 day D-rest for all lagers as well as clean ales such as Kolsch at about 65- 70 degrees. It gives the yeast time to clean things up. It generally also causes an increase in fermentation activity and lowers the FG. I have always heard that it only needs a half day but I have found that by starting a few days early I can also finish the primary fermentation sooner.
 
So I've never experienced diacetyl. I wanted to be sure I didn't have an issue with it in this beer so I performed the test today.

The result, to me, didn't necessarily taste directly like butter. It definitely tasted nutty but almost like butter pecan ice cream. I'm assuming that is diacetyl?
 
If you taste butter it is an indication of stronger diacetyl. In my experience you get more of a butterscotch flavor. I happen to love butterscotch candy so it may not be a bad thing as far as flavor goes with personal preference but in competition it is a flaw to the style. There are some ales where a low level is expected but as far as I know never in a lager. Think more like butterscotch candy. If it's really bad think rancid butter. Have you ever smelled old cooking oil?
 
There are some ales where a low level is expected but as far as I know never in a lager.

Czech Pale Lager / Czech Premium Pale Lager / Czech Amber Lager. Not sure if there are other lagers, but I can't think of any.
 
If you taste butter it is an indication of stronger diacetyl. In my experience you get more of a butterscotch flavor. I happen to love butterscotch candy so it may not be a bad thing as far as flavor goes with personal preference but in competition it is a flaw to the style. There are some ales where a low level is expected but as far as I know never in a lager. Think more like butterscotch candy. If it's really bad think rancid butter. Have you ever smelled old cooking oil?
I wouldn't even say butterscotch. It was VERY faint. I had 3 people other than me taste it and the descriptors were nutty, butter pecan, and oily/slick. To me that tells me it's a faint level of diacetyl as it's not really like butter or butterscotch. But I think it's definitely there. Better to be safe than sorry. It's going to sit for a few days more.
 
If you taste butter it is an indication of stronger diacetyl. In my experience you get more of a butterscotch flavor. I happen to love butterscotch candy so it may not be a bad thing as far as flavor goes with personal preference but in competition it is a flaw to the style. There are some ales where a low level is expected but as far as I know never in a lager. Think more like butterscotch candy. If it's really bad think rancid butter. Have you ever smelled old cooking oil?
Actually I take that back. You hit it right on the head. I smelled it again and butterscotch is spot on with the smell. Not so much the taste but definitely in the smell
 
Can you do a diacetyl test beer that's already kegged and carbed?
Of course, although by then you should already be able to detect diacetyl if there is any.

The point of doing a quick diacetyl test in commercial brewing is to make 100% sure there are no diacetyl precursors in the beer that will then turn into diacetyl with time (O2 is not required for that, just time) before the beer is filtered and/or pasteurized. Once the beer has been filtered and/or pasteurized it is microbiologically dead and therefore any diacetyl will stay in it forever.
 
So I've never experienced diacetyl. I wanted to be sure I didn't have an issue with it in this beer so I performed the test today.

The result, to me, didn't necessarily taste directly like butter. It definitely tasted nutty but almost like butter pecan ice cream. I'm assuming that is diacetyl?
Diacetyl? Oh, you'd know it.

"Diacetyl Buttery, Butterscotch, Movie Popcorn".

Think of microwave popcorn.

I remember a few years ago someone claiming they got sick/ill from eating too much microwave popcorn (as the popcorn used diacetyl for the butter flavor.). Probably didn't matter this lazy bast*rd didn't get any exercise, but wanted to blame his condition on the popcorn. Geez... it's never "my fault".
 
Back
Top