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Diacetyl/Pediococcus damnosus

Diagnosing infection and looking for suggestions:

I took a three year hiatus from brewing (apartment living) and after recently purchasing a new home I have been brewing a batch every weekend. I recently kegged two batches and bottled one. All three have an overwhelming butterscotch/diacetyl flavor which makes them taste identical. I have an immersion chiller, pitch in the mid 60s and ferment in a basement with very stable temps in the mid to low 60s, so naturally I did not expect to encounter diacetyl. Regrettably I did use some plastic buckets and a racking cane that I have had for years. I assumed that the iodophor or starsan I am using would compensate for anything lingering in these older tools.

I have resigned myself to the fact that all three batches will be dumped. I will be replacing all the plastics. Now I am curious what other precautions I should be taking. How likely is this bug to cross contaminate my other brewing tools? How should I go about sanitizing all my cold side brewing tools subsequent.

I am an otherwise experienced brewer who has only dumped a batch or two out of roughly 80+ brewed in the past so this is a major setback. Any suggestions are appreciated.

I had some kegs go bad on me with something that was giving me a sourness in some beers. I bleached all the kegs and taps and fittings. That worked

Diacetyl is not necessarily a sign of contamination. It is very common in young ferments and usually ages out. If you used the same yeast for all of these and the same low temps. I wouldn’t be surprised if it just wasn’t done.

“As yeast slow down in fermentation, they enter what is known as the stationary phase. This phase is when beer undergoes a maturation process to develop the correct balance of flavors. One of the key elements of maturation is diacetyl reduction. Not only do yeast produce the precursor to diacetyl, they also consume the diacetyl that is produced and enzymatically reduce it. Yeast reabsorb diacetyl and convert it to acetoin and subsequently to 2,3-butanediol.”

What yeast were you using? I wouldn’t have thrown these out

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Since you kegged and bottled I don’t think it would be the kegs. I would do a deep dive into everything that contacted the beer and replace or clean heavily.Unless your taste buds are completely off, I think you’re right about the infection.

Did you pitch enough yeast, do a diacetyl rest? Those are the first two things I thought of. Definitely can’t hurt to clean and sanitize your equipment. What is your water supply?


I just responded to how to clean the kegs but it’s true since the flavor was in the bottles as well it’s a pre package problem but I think he knows that as he said he is replacing his fermenters and racking tools. I think he is worried that now he has infected his kegs and bottles so they need cleaning. This is not a new brewer sounds like he knows what he is doing

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Thanks everyone for the input.

The yeasts were US-05, S-04 and OYL-057 (Kveik). Ales were pitched at 65 and Kveik was pitched at 85.

I am unfortunately convinced that this is an infection since all three beers taste identical.

I will bring the beers up to 70F and see if a late diacetyl rest can be accomplished. Re-sample the beers in a couple weeks and see if things have improved though I doubt it.

Humbling experience, but I will replace equipment and do some deep cleans to ensure this doesn’t repeat.


It could be something simple as sanitation. I like to use 180-190 degree water with star san for sanitizing. Maybe your temps for the wort for the yeast.

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