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Jun 08, 2022 View:

Bacterial Fermentation and Off Flavors

Anyone have a good resource for the effects of bacteria in a fermentation on flavour for various bacterias? Also, information on the final distillate affects would help.

And more specifically, I ran a corn mash that had some sort of bacterial infection through a stripping run and the results was a golden colour and smells different than usual (I would describe it as sour smelling but not vinegary). Anyone know what bacteria would cause this and what I should do with this? Will it dissipate with time? Will it be cut with the heads and tails cuts?

The aroma has dissipated slightly in the past 2 hours if that helps.

Thanks for your help.


The most likely bacteria is lactobacillus, but your low wines should still be clear, not yellow. Did your still puke?


This blog is an interesting read, and it addresses the influence of lactobacillus on the flavor profile of whiskey:


The most obvious places to look in the distillate for bacterial contribution are in the late heads and early hearts, and this will be due to esterification of the carboxylic acids produced by the bacteria. I've run a good number of these combinations as Fischer esterification reactions in a glass lab to know the table is roughly accurate. The ethyl esters are easiest to pick out in the late heads fraction, but be aware that the acetic acid esters will almost always dominate. Depending on what you are looking for, you might find that the bacterial contribution may very well be positive, and not negative.

For example:


Also - Lacto will not produce a colored distillate.


Thanks for the information!

The yellow colour is only visible in large quantities in the tank and hard to see in a small sample. See attached.

The colour and odor were definitely from the beginning of the stripping run so I assume that they are in the heads.

The still did not puke at all in running them.


Great chart James Bednar - thanks for sharing!


Wow that is a crazy yellow. Your low wines are very clear though. Usually low wines are a milky white off color coming through in the tail section. Don't know what the yellow is but are you cutting your strip short? Should be milky looking if going all the way through the tails. Atleast, that's how it works over here.


I did cut a little short on this run although I don't usually get much milky color anyways but do get some.


In case anybody reads this and wonders that happened....

I had a second mash that produced similar (though not as pronounced results). I combined those with 3 other stripping runs and ran through a spirit run yesterday and found no issues in the spirit run. It is possible there re slightly more fruits flavours in the early hearts but nothing extreme.


It's not the reflection off the lights is it? I'm sure you already thought of that.