I brewed a 3.5 gallon batch of Kolsch this past Saturday, pitching a 1 liter starter of WLP029 at 60 degrees and fermenting at 62. I pulled a sample last night to keep on hand for a fast ferment test - 2 days after pitching, the gravity had gone from 1.052 down to 1.020, but I noticed a very strong nail polish remover smell in the sample, which I believe is caused by ethyl acetate, although I’ve never had this happen before.
Is it common for ethyl acetate to show up like this during fermentation? Is it something that will eventually be cleaned up by the yeast? I’m at a loss here - I pitched a good amount of fresh yeast into cold, mix-stir aerated wort and fermented on the cool side. How did I end up making nail polish remover?
Solventy aromas can be from too hot a fermentation temperature (various fusels), but that shouldn’t be an issue at 62F. 1L of a starter for a 3.5 gallon batch is also on the high side for an ale. If it is ethyl acetate, that’s going to be formed from ethanol and acetic acid which means a potential acetobacter infection. I definitely wouldn’t dump it yet, but monitor it. Unless you’re super sensitive to it, it’s not a normal byproduct.
It might be caused by too big a pitch. The theory is that acetyl CoA is used for growing yeast, but that if it is not used to grow yeast then it will make esters.
www.yeastcalculator.com says I need 170 billion cells for a 3.5 gallon 1.052 hybrid ferment. Using Kai Troester’s stir plate model, a 1 liter starter is predicted to give about 222 billion cells. This doesn’t sound like a significant overpitch, especially when Jamil’s model only predicts 187 billion cells for a 1L starter.
I’m wondering if it’s an acetobacter infection, although I’ve never had one before and my kitchen is damn near spotless with no fruit flies to be found. Everything gets a soak in PBW followed by a hot water rinse and then a soak in star-san before I rack from kettle to fermenter.
I’m wondering if too much kettle trub made it into the fermenter? I’ve been a bit lazy about that lately, racking everything except the thick sludge at the very bottom. I’ve done this on several batches now without issue, but maybe my luck has run out.
I’ll give the beer another week in the fermenter and see what happens. After that I’ll do a 180 F hot water sterilization of my equipment and try another brew.
In my humble opinion (an it’s just that), in the absence of a confirmed infection, what you are experiencing is the result of stir plate-induced stress. I have mentioned many times that stir plates subject the cells to shear stress, which is why I no longer use a stir plate.
I say he is still jumping to conclusions. He seems to be basing his impressions off of a sample pulled for forced fermentation and not a finished beer. The other impression is off an “air lock” sniff. Neither of these things are very reliable forms of analyzing a finished beer. Now you are jumping to conclusions too, Mark.
I think you’re jumping the gun with a diagnosis of a problem in the midst of fermentation. Let the beer finish fermenting before you declare it a disaster.
Exactly! How many batches do you have under your belt? Fermentation can throw some funky, including sour, aromas. You can sort of think of fermentation as a form of “controlled rotting”.
More than likely so… If the aroma has changed from nail polish to vinegar, then it would appear that the culture is splitting ethyl acetate back into its constituent compounds; namely, ethanol and acetic acid. I have personally never experienced what the OP is experiencing. It will be interesting to read about the final results.
I dumped the batch this morning. It smelled awful, unlike anything I’ve made before, and I’ve used this yeast multiple times. It would have been interesting to see the final outcome, but I have limited fermentation space and haven’t brewed anything in months due to the fact that I recently moved. Making another batch is not a big deal - at this point I care more about getting good beer back into my empty pipeline than making an experiment out of this.
Even after a soak in PBW followed by star San, my speidel still smells like vinegar now.
So I re-brewed the same recipe and fermented in a different vessel. The beer has been kegged a little less than a week now, but also exhibits a slight nail polish remover smell, but no vinegar. The nail polish remover smell was quite a bit stronger when I first kegged the beer, though. I am reasonably certain that this beer is not infected.
I had an extremely vigorous fermentation - from 1.050 down to 1.012 in 4 days. I left the beer in primary another week after FG was reached before kegging. Perhaps overpitching was to blame after all, or maybe it really is stir plate induced stress? This would be the first time I’ve ever gotten that, and I use my stir plate to make a starter for every batch. I pitched a decanted 1 liter starter of WLP029 into 3.5 gallons of wort and set the regulator to 62. If there was an excess of acetyl CoA rapidly produced early on but not needed for reproduction because either the initial cell density was too high or the malt sugars metabolized too quickly, then I suppose it could esterify into ethyl acetate. I’m just a little shocked, because I often hear about people getting away with large pitch rates of WLP029 and getting a cleaner beer, not an estery one.
The 15 or so batches prior to this one have been lagers that turned out great, including one that got a gold medal in a BJCP comp. I guess I just got used to making big starters.
I’ll likely try to re-brew this recipe again soon, perhaps with a smaller pitch rate and a slower setting on my stir plate.
