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Sep 24, 2011 02:37 PM

Bacteria/Mold/Whatever Growth in 49% ABV Rum?

I just found a bottled of Scarlet Ibis (49% ABV) in the back of my liquor cabinet that I'd opened up, removed a few ounces of, and forgotten about -- maybe a year ago. There are a number of little off-white blobs floating around in the bottle, which certainly weren't there before. I Googled around and most of the information is not only contradictory but also not at all authoritative (it's tough to trust anything found on Yahoo Answers).

Anyone here have any idea what could be going on? Were there a bit of particulate matter in the rum I would expect sediment at the bottom of the bottle, not floating around. Is it possible for any kind of organism to survive in such a high ABV environment? And if so, is it still safe to drink the stuff? Obviously I'd rather not send it down the drain!

Thanks all.

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  1. You don't trust Yahoo Answers but you trust the yahoos on Chowhound? ;)

    You might try Darcy O'Neil at Art of Drink ( While he is a chemist and not a biologist, he might well have an answer.

    Absent another answer (JMF???), I'd filter it with a coffee filter. Make sure your guest drinks first. ;


    -- | Craft + Collect + Concoct + Categorize + Community

    2 Replies
    1. re: EvergreenDan

      Your comment about Darcy O'Neil reminded me that one of my friends is a microbiologist. Just e-mailed her. I'll report back on what she has to say on the topic...

      1. re: davis_sq_pro

        And my friend agrees with the wisdom of Yarm:

        "At that concentration bacterial membranes and such are totally messed up and destroyed. Although there are extremophiles that can survive environments like high temperatures or salinity, I am unaware of anything that can grow in that high a concentration of alcohol. It should be safe to drink..."

    2. I have a degree or two in biology, biochemistry, and microbiology. 70% is what is considered fungicidal and bactericidal when sterilizing tools and equipment for tissue culture and animal surgery. Living fungus is more sensitive than the spores (bacteria is the most sensitive of the bunch). I have seen this range written as 60-90% (100% is less effective for some water actually helps to kill spores which can be rather shielded from harsh environments).

      I have heard of mold growing in 20% ABV liqueurs. It grows slowly and doesn't amount to too much (often a brown fluffy haze or precipitate at the bottom). But here there is a lot of sugar for energy source and often nutrients from the infusions.

      Will fungus grow in 49% ABV spirits with no sugar added? Doubtful since it is rather close to what would kill them (besides the lower amount that will just stop their growth) plus there is little to use as energy and nutrients. I cannot think of any 40% liquors that have grown microbes. I have heard of precipitates from poor filtration, cork disintegration, oils coming out of solution, or other though.

      6 Replies
      1. re: yarm

        Thanks, Yarm. Sounds like application of a coffee filter is all I need to be on my way to sipping a bit of rum punch.

        1. re: davis_sq_pro

          If it smells good and tastes good, drink it.

          I had a bottle of St. Germain get a brown precipitate. I was told that it was mold by JMF. I figured it was botanical precipitate. Regardless, I finished the bottle (although I did not use the last 1/2 oz) and I was no worse for wear.

          A lot of the fungicidal alcohol percentages are to kill fungus so it doesn't grow once introduced into a happy environment (tissue culture medium, surgical incision, etc.). Fungus doesn't like to grow in many harsh conditions that will not kill it. And spores can be resistant as I mentioned before. Alcohol and liqueurs probably have a fraction of microbial growth than practically everything else you eat and drink.

          1. re: yarm

            Really, I said that the St. Germain had mold? It could because it is only 20% abv. but I think that the brown precipitate in early bottles of SG are from organics settling out.

            1. re: JMF

              Might not have been you but I remember someone telling me that. The reps went from saying that it had an infinite shelf life down to 6 months. When we compared the dregs of our old bottle (close to 2 years old) to the fresh one, it wasn't that different. A degree of brightness in the new one, but the old one wasn't skunked or anything. Brown precipitate and all. I remember declaring that it was botanical matter coming out but someone was insistent that it was mold.

              1. re: JMF

                It was in this thread:

                "Even if the alcohol didn't evaporate, mold can grow in alcohol, there are some very alcohol resistant strains. Even up to 40% abv., many time particulates in spirits and liqueurs are mold."

              2. re: yarm

                Mold can grow on the SURFACE of a high abv. sweetened spirit if the bottle is left undisturbed for a long period of time. Small amounts of sugar can collect on the surface, acting like a barrier, and the mold can grow on that, then as it gets heavy enough, or is slightly disturbed, it can sink into the spirit. So this may be the case.

                But it is probably colloids flocculating out of suspension. Exactly what is hard to tell, but a combination of sugars, organics and botanicals, esters, glycerol (glycerin), etc. I would think that it's most probably glycerol, or the fatty acids esters of glycerol. Glycerol naturally occurs in spirits, and is added to many for smoothness and a rounder mouth feel.

          2. I agree with others that it is almost impossible to grow any microorganism in 49% ethanol.

            Keep in mind when folks are talking about higher percentages for killing, 60-90% ethanol is what it takes to guarantee to kill 100% of a living culture.

            The amount to INHIBIT new growth should in theory be much lower.

            That said, there are some fungi that NEED a small amount of alcohol to live. Even they would not likely survive in 49% ethanol:


            Heck we could always try to culture it here in the lab for you...

            My guess is that you have some precipitate which happens to float. Uncommon, but not unheard of. Thus as the precipitate forms, it floats to the top.

            1. It coud be throwing off sugar crystals. Very little will grow in 49% alcohol. This from a guy who just fished a dead spider out of his single malt scotch and kept on drinking.

              9 Replies
              1. re: kagemusha49

                it wasn't Octomore Scotch by any chance was it?

                1. re: kagemusha49

                  Which reminds me of the glass of Jim Beam I was once served FULL of fruit flies, like dozens, which I did not drink...

                  That said, one spider, fish it out, forge ahead. Heck I see a new beverage category. Spider venom infused single malt.

                  1. re: StriperGuy

                    Yechh on the fruit flies. That's like the time many years ago when I learned why you don't leave speed pour spouts in bottles for long stretches. I was given a bunch of half-full bottles of various liquor by some roommates who were moving. The bottles had been sitting on a shelf with the uncapped speed pours probably for months. I had made a drink and was just starting to take a sip when I noticed all the black dots in the bottom of the bottle, "hey, are those...?" Spit, then dumped all the bottles in the sink immediately.

                    1. re: nickls

                      That's exactly the scenario at the dive bar where I had my fruit fly cocktail.

                      1. re: StriperGuy

                        My fruit fly experience was a glass of Appleton 21 at a supposedly upscale bar in the Boston area. Not fun, especially given the reaction from the bar: the bartender just kind of shrugged when I showed it to him, removed the half-filled bottle from the shelf, and took it into a back room. He returned and poured me another drink. Later, some other guy emerged from the back carrying a "new" bottle of Appleton 21 that they put on the shelf -- but it was tough for me to miss the fact that it too was only half full...

                        I'm sure that straining the dead flies out of liquor is a fairly common practice at a lot of places, but I really wish they'd done it after I was out of sight. I'll never return to that bar. (A comp on the drink, or at least an apology, wouldn't have hurt either.)

                        1. re: davis_sq_pro


                          I totally agree that a few fruit flies likely do no harm, but noone wants to see that.

                          In the dive bar they dumped the bottle, cracked a new one in front of us, and comped ALL of us a round even though only I had order the Jim Beam to begin with.

                    2. re: StriperGuy

                      That could turn you into a superhero.

                        1. re: phantomdoc

                          Could be - it WAS a loxosceles (brown recluse) - they are common around here.

                    3. is the Scarlet Ibis chill-filtered? I read that sediment can form in non-chillfiltered Whisky if it is kept in a cool place. I would think if the fatty acids were congealing they would float.

                      1 Reply
                      1. re: ncyankee101

                        It is specifically labeled as NOT chill filtered. But it was not kept in an especially cool place -- in the back of a cabinet in my kitchen.