Acetone smell from brown ale

[brianpablo]

I made a nut brown ale about a week ago, chilled it to about 65 and pitched with rehydrated Nottingham. Nothing happened for nearly four days, until I started to see signs of krausen forming. Now there's a nice healthy crop of krausen on the top, but I just got a really strong whiff of acetone coming out of the airlock. I'm assuming the fermentation lag may have risked an acetic bacteria contamination, which I'm guessing is what I'm smelling. The temperature gradually rose during the four days of non-fermentation, and had reached about 74 by the time the krausen was forming. That's hotter than I'd like it to be but doesn't seem to be an obvious reason for an acetone problem. I've cooled it down to about 72.

I've seen some threads about Nottingham being slow to take off, but none seemed to mention this particular consequence. My instinct is to leave it, but I don't get the sense that the acetone smell goes away ever. Would help to know if there's any specific post-infection treatment to keep this sort of thing from coming back.

Thanks.

 

[Queequeg]

My first thought is fusel alcohols and acetealedyhde.

 

[kombat]

I agree. Nottingham is notorious for preferring cold temperatures. 72-74° is much warmer than I'd ferment with it, you're likely smelling fermentation by-products. The long lag time may have been due to underaeration (how did you aerate the wort?), which would additionally stress the yeast.

 

[brianpablo]

I aerated with the aquarium diffusion stone and the usual pump, for about 20 minutes. It may be the temperature. I had planned to ferment at 65 but after four days - that's a long time in my book - I thought perhaps it was too cold. I can try pulling the temperature down below 70, but sometimes I worry about those abrupt temperature changes as well. It's been in active fermentation for about 24 hours now, so perhaps there's a chance to limit the fusel alcohols.

 

[Queequeg]

Bring the temp down, but IMO the damage is done.