The most commonly agreed-on method of keeping your e-liquids fresh is to keep them away from heat, light, and air. Store in a cool, dark place and most will keep for quite some time. E-liquid manufacturers might package their juices in dark bottles; which serves the same purpose as it would for a beer brewing company to bottle their brew in dark glass. Exposure to light and heat can cause oxidation, which causes darkening in the short term, which is purely cosmetic. But in the long term this can effect the flavor of the juice. It’s a better bet to store the e-juice in a cool, dark, place to keep it fresher longer. Opinions vary among commenters on the internet and vape-shop owners as to whether or not to refrigerate e-juices and why, but more tend to agree on simply storing in a cool, dark place.
The e-juices which are used for vaping are commonly made of PG (Propylene Glycol), or VG (Vegetable Glycerin), or a mixture of both. VG juices are considered the way to go for making huge clouds. PG juices aren’t as thick in consistency and can come in handy because they burn in such a way as to allow for discreet public vaping. Many popular juices are a mixture of the two. Vegetable Glycerin is made, in part, from vegetable oil. Propylene Glycol is a byproduct of petroleum. So, PG and VG are different consistencies but both are of an oily nature. Refrigeration poses issues ranging from microbial material being present in the refrigerator in the form of condensation, lights which come on intermittently throughout the day, and possible clumping caused by the cooler than room temperature environment having their effect on liquids of varying viscosity levels. These factors by themselves present more potential obstacles than simply storing the e-liquids in a cool, dark place.
That having been said: refrigeration for brief time periods can be used without degrading the juice’s flavors if they are only to be refrigerated for a couple weeks, during which time the juice will be vaped. E-juice isn’t exactly like wine in the it doesn’t improve with aging. Wine is also stored in a cool, dark place. E-liquids, some manufacturers suggest, can benefit from a “steeping” of limited duration, which is best allowed to happen in the most agreed upon place for optimal storage: one that is cool and dark, without exposure to air and heat and light. The flavor of the juice is the component most likely to suffer from improper storage over time. Refrigeration won’t likely harm e-juice, but it definitely won’t do it any good.