To fridge or not to fridge. Here is my thinking about this, in no particular order, as a chemist of 30 years.
1. I don't think there is anything in e-liquid to "go bad", per se. It is PG, nic, and some trace tobacco compounds, and flavor. All simple chemicals that will not react easily in the cold. However, just like keeping salsa in the fridge, anything that comes in contact with the e-liquid must be CLEAN, CLEAN, CLEAN. Like a syringe or dropper. No touching it, licking it and sticking it in, or anything else that WILL have ambient mold, bacteria, etc, on it. Salsa, sour cream, bean dip, which have come in contact only with a clean spoon will last 10x longer than if you get sloppy, lick the spoon, and then use that to spoon out some more. I would imagine the same is true for e-liquid. Things can grow in PG or VG. Nic will kill many ambient baddies, but not all.
2. Cold liquids WILL condense ambient water vapor from the air. So if you store in the fridge, I would think it would be best to let it warm to room temp first, then open it. This will keep less water from naturally condensing on it. PG and VG have OH groups, which will hydrogen-bond with water easily, even at room temp, and cold PG or VG will do it even more.
3. Nicotine in of itself has a VERY long shelf life. I know this because my brother used nicotine in pharm Alzheimers Disease studies, and many of the nic lots were > 10 years old, with zero degradation. Expiration dates on nic gum, lozenges, etc, are just there because by law they have to put a 1 year exp date on all pharm drugs...and it gets you to throw out what you have and buy more, as a bonus to them.
4. PG or VG are both stable forever if they are clean. But clean is relative, and I do not know how sterile the conditions for packing and shipping juices or pure PG/VG are.
5. Wiki lists the freezing point of VG (glycerin) as 64 deg F. Question: can one use VG e-liquid in the cold? Does it freeze? Other components in VG will lower the freezing point, especially ethanol (vodka), water, and flavorings...anything that dissolves in it will lower the freezing point. I do not know if frozen VG is more or less dense than liquid VG, but if it is more, then expansion in the cold could rupture the container, like water-ice will. The viscosity of cold VG is considerably higher when cold (like 4x).
6. The liquids involved in e-liquids are not 100% miscible with each other, especially some flavorings. Separations in the cold can occur, but that does not necessarily mean it is bad, just needs to be shaken or mixed after warming to room temp, or a touch higher.
7. Home made nic juice from tobacco will contain plant material to some extent, as this is natural in any plant alkaloid extraction. Plant material WILL go bad eventually, like rotting leaves.
8. I would not recommend microwaving e-liquid to warm it. Reactions could occur, and we do NOT want reactions!!
So I intend to store my unopened high-nic juice reserves in the fridge, and only open one bottle at a time when I want to use it, after bringing it to room temp. After that bottle is opened, it will only have contact with very clean transfer equipment (syringe, dropper, pipet), and after that equipment is used it gets washed and dried thoroughly. Then the bottle will be closed and stored back in the fridge if it is a large amount. I do not yet know what the effect of oxygen is on e-liquid components, but I am looking into that and will post what I find later.
Vape on, brothers and sisters!
