Please help me diagnose my infection and its cause

[Coxy]

I fermented 46L of IPA split across two fermenters, and one has picked up an infection, unfortunately. In my 12 years of brewing, it's the second time I've had an infection that required the beer to be tossed out. It's a little more interesting this time in that I have a 'control' as such in the un-infected beer. I'm definitely not practiced at picking up exactly what the infection is, but I would say it tastes something like acetone mixed with some soap.

To add to the mix is a 5L demijohn that I was making a small batch in of a completely different beer (a hoppy brown ale) which has also picked up the exact same off flavour.

There is no visible infection in either batch of infected beer.

My two big fermenters are just standard off-the-shelf LHBS plastic ones. All three batches were in the same fermentation fridge, fermenting at the same temperature (give or take some differences in the fridge). All three were using a 3rd (or maybe 4th) generation washed yeast which had been sitting in my kitchen fridge for quite a while.

I can probably rule out any part of the pre-fermentation process imparting off flavours such as tannins etc, as I've been using the same or similar set up for a long time now, and if this was an issue then both big batches would have the same flavour.

What do y'all think it could be? My suspicion is that two of the jars of yeast may have picked up some wild friends while sitting in my kitchen fridge.

 

[homebrewnewb]

acetone and soap, any more to go on? soapy could be on the cake too long but i doubt that, can you describe the acetone facet a bit more?

one FV could not be as sanitised as the other, but it is starting to sound like one FV was warmer maybe than the others.

if it were a wild one, i would have thought it would have had a tart aspect to it, anyway please try and get some more details.

as an aside while i haven't been brewing as long as you it's pretty shit when your process gets usurped by a microbe.
identifying what it is isn't going to bring the beer back, it's *******, but identifying where the process has gone wrong - you'll need to get on to that.

 

[Coxy]

Unfortunately, tastes like this are really hard to describe, as it's not something that I would willingly put in my mouth usually. It has a strong unpleasant smell that's kind of part cleaning product, part turps. I'll take a sample along to my next brew club meeting and see if some more trained palates can help.

In terms of being on cake too long - no chance, it has only been on there for three weeks and the krausen has only just dropped.
In terms of one FV warmer than the others, this is actually fairly possible. The non-infected beer was on the upper shelf in the fridge, and the two infected beers were at the base of the fridge. I find it highly unlikely that an infection would occur in the colder of the vessels, however.

Some more information: The yeast took much longer to complete primary than usual. It was about two weeks before it dropped within 5 points of final gravity. It dropped from about 1.050 to 1.035 in a couple of days then stalled for about a week (with krausen on top), so I increased fridge temp a little and it very quickly (~2 days) dropped down to under 1.020.

 

[homebrewnewb]

it temperature is the culprit here, then i suppose that is good because it's not an infection and if we're correct and it's hot alcohol/fuseals then that can kind of age out, not great for your brew, obviously.

but that means you've got a temperature dynamic in your fridge you're not aware of.
or, something in leaching into the brew.

if it is fuseal alcohol it will diminish over time as you probably know, but if you think it's an infection i am not sure what would cause that apart from stressed yeast.

yeah, sorry about asking you to taste it again too, i wouldn't either, be good to hear what the other FBs in the club say, however.

 

[MHB]

Everything you have said points to stressed yeast, that's no guarantee that you don't have an infection in there to.
Any beer that hasn't reached FG in seven days has been under pitched, given the time taken to reach FG and the soapy acetone flavour descriptors it sounds like a good bet.
As for the bottom fermenter being the troubled one, there can easily be 5oC difference between the top and bottom of a fridge, its quite possible that the yeast lowest down was colder than expected, often so cold that it is hovering around the yeast dormancy point. Yeast being turned on and off (metabolically) will cause lots more stress = off flavours.

FFS put a small fan in your fridge, it will break up the temperature stratification, keep the temperature even and even improve the rate of cooling.
Mark

 

[Coxy]

Thanks Mark - I do have a fan in the fridge, but there is still some temp difference and some improvements can be made. In addition, I didn't put a heater in there for a few days and it was down at the 17C mark (at the top) for a while. This makes quite a lot of sense. I'd say the flavour is an enhanced version of the off flavours in my very early brews - what people often call 'that homebrew taste' which has been amplified, and something I haven't experienced since having temperature control.

If it IS due to stressed yeast and not an infection, the flavour is likely permanent, I take it? If there's a chance that it would condition out, I will give it a go.

 

[MHB]

It wont get much better, some flavours might diminish but most wont. As beer ages you will start getting age flavours.
I have never found a heater necessary, a 20W fan is a 20W heater, just running the fan will heat up the fridge, make sure your air circulation around the fridge is good, I had a (now dead) infra red thermometer and just spot checking the internal surfaces of the fridge gives a pretty fair indication of how the air is moving, should be the same or close top, bottom and sides.
Mark