Fruit Fly Infection?

[Reisende]

Ok, so tonight I was going to bottle an oatmeal stout I brewed 4 weeks ago. I pop the top on the fermenter, and I get a sharp, kind of sour and very "fusel" kind of smell. I take a hydro sample and taste it: tastes vegetal, tart (not really sour), and like I fermented it at 85F (maybe fusels, ethyl acetate??). It also attenued at almost 76% ADF (1.055/1.013), which is much higher than it should have with 1318 and the amount of crystal and roasted grains in the recipe.

Stats: JZs McQuakers Oatmeal Stout, partial mash, used WY1318. Fermented at 68F in fermentation chamber with thermowell, max temp swing 0.8F. No secondary, right at 4 weeks.

Only thing I can think of, is that I found 3 fruit fly's (see below) in the airlock! I cant seem to figure out how they got there, they were not in there two weeks ago when I checked it last.

Here are some picture of my fermenter, a few yeast rafts, and some fairly thick trub along the side, kind of gray. This trub smells just like the beer.



I checked all my notes, I did use the same fermenter bucket for another batch (pumpkin ale) that exibited the same kind of tart, fusel'ish and vegetal off flovor/aroma, and also attenuated lower than was expected. This batch also had a fruit fly in the air lock, but I chalked the issues up to the large amount of pumpkin that I used and the US-05 with its high attenuation.

Does anyone have any ideas/suggestions/similar experiences? I am going to wait for some feedback, but I think this batch is getting dumped, it is un-drinkable.

 

[giraffe]

Sounds like an infection. Probably bacterial. Since it was in two batches, id clean all of your equipment with the utmost thouroughness.

Fruit flies often drown in airlocks if the house they are in have them. They will be attacted to the smell of fermentation. Its not a concern as they are in the airlock, they never reach the beer-- which is the point of the airlock. The presence of fruit flies is likely incidental.

 

[Reisende]

I would agree with you completely, except these "infected" batches are separated by 5-6 batches of perfectly fine beer in between. They did use the same fermenter, but that also has been used for other batches.

I guess it could be coincidence, it just strikes me as odd. Do you think it could be acetobacter? I have never (knowingly) tasted it before, so I wouldn't know.

 

[giraffe]

Could be. Acetobacter is vinegar bacteria, but sometimes it just tastes cidery in small doses. Im not an expert on such matters, there are other bacteria that produce cooked cabbage smells. Are you putting vodka or starsan in your airlocks? otherwise if you get suckback or knock the airlock, dead fruit fly water can go in the beer.

 

[Reisende]

I always use Starsan. I suppose after a month the level could have gotten low enough to expose some of the holes in the bubbler piece, which may have left a path for bugs.

 

[JimRausch]

Fruit flies in the airlock- no problem, you drowned the little buggers.
Fruit flies in the fermenting beer- problem. As you guessed they carry acetobacter which will turn your alcohol to acetic acid. Malt vinegar. Good stuff, but who needs 5 gallons?
To me your pictures look OK. To me, that 68* fermentation is a little high and could have led to some higher alcohols and esters being produced. I would probably package it and see how it turns out with some age.

 

[Reisende]

That's what I did, bottled it this morning. I have not used 1318 before, although WYeast says its good up to 74*.
Something was wrong, that's for sure. And it wasn't just something that needs to "age out".

I was going to brew today, however I decided to uber-clean all of my equipment instead. Probably the safer bet, not as much fun.

 

[jfr1111]

I have stopped using water in my airlocks and use neutral grain alcohol now. I'm pretty sure the tiny amount of acetobatcer on a fruit fly won't survive the trip in 191 proof spirit.

 

[dcp27]

That's what I did, bottled it this morning. I have not used 1318 before, although WYeast says its good up to 74*.
Something was wrong, that's for sure. And it wasn't just something that needs to "age out".

don't invest too much thought into those upper temp ranges the labs say. very few strains are 'good up to 74', pretty much just belgians/saisons, and even those you generally don't want to start that high. most english yeast are downright awful over 68F. in the future, keep your temps down. check this thread out for tips on english yeast: https://www.homebrewtalk.com/f163/b...on-temps-profiles-cybi-other-thoughts-221817/