I’ve got a bottle of food grade glycerin in the cupboard that is marked best before some date in 2006. It still looks and smells OK and actually I don’t even want to use it for food purposes - I’m just curious as to whether it’s something that does degrade over time.
So does glycerin ‘go off’?
only when nitrogenated 
The only thing that may have happened is water absorption. Chemically, it is pretty stable.
Si
If it’s food, it must have an expiration date; that doesn’t mean the expiration date is real. As the owner of a cannery said when that kind of laws were enacted in Spain “if a can is bad, it’ll show before one week; if it’s good it can last decades, but we’re having to say five years because that’s the legal maximum.”
One of the “problems” of the chemical, pharmaceutical and food industries is how to define the shelf life of a new product. If it’s relatively short (the few days of Pasteurized milk, the few months of UHT milk) ok, but… what do you do if you know it can last “more than a year, we have similar products that last about 18 months and others that last ten years”? Well, you set it as 18 months for the time being and make it bigger once you start getting real data (if the real data says 18 months is too short, of course). For some kinds of products, the maximum possible date is set by the Government; there’s been edible honey found in Egyptian tombs, but the Spanish Government doesn’t accept shelf lifes over 5 years for either foodstuffs or medication.
Only if you first ‘nitrate’ it.
My intention is to mix a small quantity of it with potassium permanganate (it reacts and bursts into flame) - I tried this the other night and it just didn’t work, but I think my ingredients might have just been too cold for the reaction to get going.
Use just a drop of glycerin to a pile of permanganate. Things get very exciting if you add powdered magnesium to the permanganate.
This may also be impacted by the presence of water in the glycerine.
It is a fun reaction, though.
Si
I use a 1:1 mixture of glycerin and ethanol. It’s allso possible the permanganate has degraded…Its a good oxidizer and may have reacted with the container. Is it purple, green or brown?
But my first suggestion is to add ethanol to the glycerin (I think 95% will work but I don’t know for sure.
Sigene (chemist, former chemistry teacher…but more relavant…camper and designated fire starter)