Disclaimer: I don’t know the science behind this, this is an email from the sweet Linda (I am convinced she bathes in Ethyl Maltol for extra sweetness) from The Perfumers Apprentice which I’ve been allowed to post. The summary is my work but only based on what was mentioned in the email.
This was emailed in direct response to a question I had and as such the writing style is not the smoothest but there is a mountain of good information that I wouldn’t feel comfortable editing-
Concentrated flavors do not spoil, or go rancid like fruit juices can.
But under certain conditions, they can change.
Basically, the flavor producer tells me is that these flavors have at least six-months to one-year shelf life when they are not continuously opened. It is not necessary to store them in the refrigerator, but I don’t think that this would hurt them. But sometimes refrigeration can cause re-crystallization of flavors that have a lot of the crystals like ethyl maltol in them.
Here’s some background:
Every concentrated flavor is a mixture of raw materials, and every flavor blend can act differently. For example, vanilla flavors characteristics are going to have different storage times than fruit flavors. Here’s the reason.
Vanilla and Candy e-juice flavors are mostly made of large molecules like vanillin, ethyl vanillin, etc.
These molecules are not more volatile and tend not to escape your bottle when opening it. They will be stable. Fruit flavors, on the other hand, are made of much smaller molecules in general. Whenever you open a bottle, it’s the lightest and smallest molecules that escape and reach your nose quickly. Over time when you open a bottle over and over again more and more proportion of these lighter molecules leave the bottle and eventually the character of the flavor will be changed. This doesn’t mean the flavors spoiled; it’s just different.
So this is one piece of advice if you are going to store a flavor for a long period of time. Transfer the flavor to smaller bottles that you will not have to open over and over again.
Also, when a flavor is warm when you open the liquid bottle even more of the volatile molecules will escape. Much more will escape than if the flavor was cool. This is true for all liquids when liquids are heated the molecules are much more easily converted to their gaseous state. So, in general, it is a good idea to keep the flavor cool though I don’t think refrigeration is always necessary.
Also, in general, it is best not to store these flavors long-term in plastic.
The plastic that larger sizes in ( 4 ounces or above), is very resistant HDPE plastic, which is interaction with the flavors.
But even with HDPE plastic, I really wouldn’t recommend storing them for longer than a month or so. It’s much better to store things long-term in the glass.
Also, it is not a good idea at all to store the flavors with the plastic eyedropper caps on the bottles. The rubber that’s used with the eyedroppers is extremely soft and interacts
So here’s the summary.. my way:
The little bottles of flavorings contain magic; it’s in small itty bitty particles in some carrier liquid. They try to escape when they are frequently opened especially in the heat so they can have a little party by the pool with the other magical creatures.
Keep them in glass bottles when possible.
The ones used frequently but in small quantities are probably better to split into smaller bottles, so they don’t go bad.
They can recrystallize in the fridge, but they will “dissolve” when reaching room temp again
Fruit flavors get muted faster than others.
For 120ml e-liquids of 100mg solution divide it into two 60ml bottles and keep them both in your freezer.You can keep all of your PG/VG/Nic out at room temp over a year without any problem, after which I don’t know what happens because I’ve never had a flavoring for that long
Rubbery eye droppers are the spawn of the devil; they want to hit you in the face and steal your mods.. avoid!