Liqueur preservation..

[Bearpig]

Howdy folks,

I've been making a brandy based cinnamon/vanilla liqueur for years and never had any problems with it until now.

Batches vary depending on what I have on hand, but typically it starts off with around a 55-60% ABV brandy which I infuse with cinnamon/cassia/vanilla, blend to taste, and then combine with caramelized sugar and honey and a dash of glycerine until it ends up as around a 28-30% ABV liqueur. Typically I just cap it in screw-top washed/sterilized liquor bottles (like Jaeger, etc) and I've never had any problems with it until now.

This time instead of capping it completely airtight, I left a bit of airspace on top of the bottles and capped it with a natural cork about halfway inserted, figuring this would let them breathe/age a little.
Fast-forward a week and I have some slight white film growing on top on most of the bottles, kindof like a bacterial infection on wine.

What's going on? How is this even possible on something that is at least 25% but more likely 30% ABV?
Anyone encounter anything like this and have a potential solution?
Thanks!

[BoisBlancBoy]

I have to assume that a mistake may have been made and the ABV isn’t where you believe it to be. If the ABV is as high as you say there wouldn’t be any bactierial growth. Unless it’s not actually a growth and your mixture is just separating/stratifying out.

With your added ingredients there is no way to test actual ABV now. A picture of them might help diagnose the issue.

[Single Malt Yinzer]

Above 25% and nothing should grow. Could be oils separating out? Heat it up and see if it melts away. 110-120F should do it.

[Bearpig]

Thank you for the answers!

I don't see how it could be any less than 25%. It started with 55-60% brandy, with which I made an infusion of cinnamon/cassia, and vanilla. Then I blended these and poured 500ml into a 1l bottle, which I topped off with honey/caramel/distilled water. So even if it lost 10% ABV along the way it can't be less than 25%.. can it?

Perhaps it is some kind of oil or sediment from the cinnamon/vanilla that I didn't filter out properly. The reason I suspected bacterial growth is it only happened on the bottles that I didn't seal completely airtight, just left loosely corked.

I blotted off the top, heated it to 55 degrees C and held it there for 5 minutes, then filtered it back into sterilized bottles and sealed them airtight. They look fine now, we'll see what happens in a week.

What's the minimum ABV that should kill all bacterial growth?

Have any of you had liqueurs go bad?

[palinkagus]

Since you added honey it might be a little bees wax coming out of solution and stratifying to the top. I had this happen to me once with a limoncello I made into which I added honey. You might want to pour it all back into a tall slender container, let it settle for a week or 2, then skim the wax off of the top.

[Single Malt Yinzer]

What's the minimum ABV that should kill all bacterial growth?

25%-30% is fine. 20% is probably ok but pushing it a little.

[Bushman]

A refractometer will give you a close abv. Also liqueurs have a much shorter shelf life due to it’s lower abv, refrigerating it will help extend it’s shelf life. What I have found is the minimum % abv that prevents growth varies depending on what research you look at. 70% is the minimum used for sterilization so anything less will probably prevent most growth but will not catch all. Most of the research I found is 30-40% will get most bacterial growth.