Ris coffee grinds added infection?

I adde coffee grinds to a 8.3% ris in secondary. I ground them finely, but did not do the vodka soak that some people use and added straight to secondary after a month. Three days later and now there's an oil like substance and a small amount of bubbles.

Is the oil an infection or from the coffee grinds? Could the bubbles be from yeast fermenting the small amount of sugars in the coffee grinds, or is it a lactobacillus or Brett infection. If I recall lactic acid fermentation does not produce co2 Only ethanol fermentation does.

I've had an infection before both lacto and Brett but this does not definitively seem to be a pellicle.


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I cold brewed some ground coffee to mask an off flavor in a stout. A couple of days later there was an oil slick in the coffee container. This may be what you are seeing.
The bubbling in your air lock is probably CO2 emerging from solution due to an increase in temperature or change in barometric pressure.

I agree... Most likely oil slick from the grounds and bubbles stirred up from adding them. Should be fine.


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Hmm thanks for the input, while we're on the topic any tips on kegging without getting the grinds into the beer/keg and clogging it.


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I typically cold crash as cold as I can go for a day or so and then use a auto siphon with the black end cap. That seems to limit any transfer.


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