acetone smell from slants

[ba-brewer]

So I went to build up a slant of wlp515 Antwerp ale yeast and there was a strong solvent/acetone aroma from the vial. The slant was about 12month and looking a bit dark. Checked my notes and I did notice an acetone smell in the jar the slants grew in. I made some beer from the yeast that inoculated the slants and it was clean, no acetone smell no phenolics.

Anyone ever experience this and what did you do?

First thought was to not use it but I figured I would see how it goes in a steps or two(only risking a little starter wort). Checked this morning and the first step(15mL) has yeast in suspension and got some foaming with a small swirl so it seems the slant did have some good cells. I did not pick up any acetone aroma.

So did some googling and solvent/acetone smell in beer seems to happen from stress or a possible contamination. As much as I would like to think it was a stress reaction sort of feel a contamination is more possible. Going to build ups the yeast a couple time to get enough to ferment a gallon of wort to see what happens.

If I do have acetobacter in the slant will it show signs in the starter or will I have to wait until after I make beer and there is alcohol?


Googling seems to show solvent/acetone to be a common thing with sour dough starters and results from stress/under feeding. I have experienced it myself with my sour dough starter when it sits for a while in the fridge without getting used. Always figured it was a bacteria thing not the yeast, but will a few feeding the starter would be back to normal.

 

[ba-brewer]

[Mod: Context edits after merging the 2 threads]

As the title suggests I have some slants of (WLP515) that had a strong acetone solvent smell, yet the beer I made did not.

I reslanted and again the slant jar had a strong acetone solvent smell. The starter I grew up from a slant did not smell solvent like just the new slants jar. I also made a small batch of beer from the starter and did not detect any acetone solvent smell. The flat fermented beer tasted normal, fairly clean flavor and slight phenolic smell (14 day ferment).

Any idea of the cause, just stressed yeast or something wild?

As the fermented beer was clean could there still be acetobacter in the beer but because of beer getting kegged at the end of fermentation and no oxygen it never turns to vinegar?

Any ideas on how I can determine if my slants are contaminated?

 

[Funky Frank]

You could sacrifice a small amount of finished beer in a jar. Just let it set open in a dark room temp spot that is somewhat sterile (never made sour beer, pickles, vinegar in that spot and no air vent blowing). If it grows a pellicle or a mother in a week, then it’s probably infected otherwise it must be due to stress. My guess is that it is not infected.

 

[RPh_Guy]

Any idea of the cause[...]?

Acetone smell (and taste) comes from high levels of ethyl acetate.

All the yeasts we use produce ethyl acetate (the most common ester). It only becomes offensive at high levels.
It's hard to say if any factor(s) may possibly have led to increased ethyl acetate production by this particular strain in this particular case.

Normally I would attribute this off flavor to wild microbes combined with high oxygen exposure, but since there's no other indication of contamination in the beer, I personally wouldn't be overly concerned about the possibility.

FYI Acetobacter does not produce ethyl acetate, at least not at significant amounts.

Any ideas on how I can determine if my slants are contaminated?

Nothing conclusive that's cheap/easy to do at home. If you have a microscope, you should take a look.
http://www.milkthefunk.com/wiki/Quality_Assurance#Quality_Control

The "forced pellicle test" that @Funky Frank suggested is specific but not sensitive since many wild microbes do not form a pellicle.

 

[ba-brewer]

You could sacrifice a small amount of finished beer in a jar. Just let it set open in a dark room temp spot that is somewhat sterile (never made sour beer, pickles, vinegar in that spot and no air vent blowing). If it grows a pellicle or a mother in a week, then it’s probably infected otherwise it must be due to stress. My guess is that it is not infected.

Thanks for the reply Frank.

I already took the hydrometer sample and put it into a mason jar with the lid on loose. Then I starting thinking that might be controlled enough as the hydro sample sat out open for a while.

I have never made anything sour, but I do have a sour dough culture that I use routinely to make bread. I use my laundry room to work on slants as it is the only room without a heating vent so I don't want to use that area.

Can I put the beer sample inside a sterilized bucket with the lid on loosely then put that in a closet or cupboard?

Would like to clarify "let it sit open". Completely open or will cheese cloth or a loose lid on a mason jar be fine?

 

[RPh_Guy]

It just needs oxygen (air) in the headspace for a pellicle to form. It doesn't need to be left open.

 

[ba-brewer]

Acetone smell (and taste) comes from high levels of ethyl acetate.

All the yeasts we use produce ethyl acetate (the most common ester). It only becomes offensive at high levels.
It's hard to say if any factor(s) may possibly have led to increased ethyl acetate production by this particular strain in this particular case.

Normally I would attribute this off flavor to wild microbes combined with high oxygen exposure, but since there's no other indication of contamination in the beer, I personally wouldn't be overly concerned about the possibility.

FYI Acetobacter does not produce ethyl acetate, at least not at significant amounts.

Nothing conclusive that's cheap/easy to do at home. If you have a microscope, you should take a look.
http://www.milkthefunk.com/wiki/Quality_Assurance#Quality_Control

The "forced pellicle test" that @Funky Frank suggested is specific but not sensitive since many wild microbes do not form a pellicle.

Thanks for your reply.

Not sure why I associated the acetone smell with Acetobacter, but it is good to know that the solvent smell is not a good indication of it.

I have used this yeast many time in the past and never noticed the solvent smell during fermentation so it stood out that the slants had the smell. In general most slants smell pretty the same as they do when fermenting a batch of beer.

I have been thinking about getting a microscope for doing yeast counts but have been putting it off. When I do get one I will take getting one capable of viewing bacteria better into consideration.

Thanks for the link, looks like a lot of good information.

Thanks for clarifying "left open".

I have had a couple contaminations in the past so I have grown to be suspicious of things that seem different and try to catch/control things early. There seems to something that don't add up so I don't want to just dismiss it. The yeast is a seasonal and not always available but was currently available so I did purchase more incase my previous sample was tainted. I will make more slants from the new vial and see if the acetone smell is reproducible in the new batch. I hope it is just a artifact of the particular yeast.

 

[RPh_Guy]

There seems to something that don't add up so I don't want to just dismiss it.

I completely agree it's smart to suspect contamination when there's an unexpected flavor or aroma, and employ some caution.
A lot of people write things off a little too easily.

If your starters with this culture continue to be free of problems, I'd say you're good to go. (Not because it's necessarily contaminant-free, but because it likely won't cause any problems regardless.)

 

[ba-brewer]

So just over a week, it appears there is a bio film forming. When I lifted the jars I notices some cloudiness drifting down from the surface so I may have disturbed it too much. Did not photograph well but it looks a bit powdery on the surface. The smaller volume jar has a slight sour smell, the other all is hard to say it seem a bit more phenolic. Small jar came from the keg and the larger jar was the hydro sample.

 

[RPh_Guy]

I'd call that confirmation there's something wild in there.