The simplistic (though not very satisfying) answer is … chemistry. While E-Liquid is really just a mixture of liquids (food grade flavorings and glycerin plus a little nicotine), that little bit of nicotine is actually fairly important. (I may be wrong, but isn’t it one of the reason for vaping?)
It is well known that nicotine, all by itself, is sensitive to heat, light (mostly the UV in sunlight) and oxygen in the air. Nicotine freshly distilled from some tobacco is almost colorless at 99.9% purity. However, put a clear glass bottle of it on a shelf by a window and it will turn straw yellow within a few days. Does this mean it is now junk? No. Now it is probably 99.8% pure and has traces of oxidized or photolyzed by-products. These by-products are often more highly colored.
Also, in the terms of chemist’s jargon, nicotine is a fairly strong Lewis base due to the presence of a pyridine ring in the molecule structure. Such bases are known to “add to” (i.e., react with) a wide variety of other chemical types. Here is where the flavorings come in.
The food grade flavorings we use in E-Liquid are often a complex combination of chemical ingredients. E-Liquid may contain artificial or natural flavors or both. For example, vanilla smells and tastes like vanilla because it is mostly the chemical vanillin. Highly pure artificially made vanillin can be found in the spice aisle of the local grocery store as “imitation vanilla”. It’s right next to the more expensive brand name “pure vanilla extract” from vanilla beans. So what? The extract contains a lot more “secondary” ingredients from the beans. These minor components are what distinguish vanillas from Madagascar versus Mexico.
Some components in food grade flavorings, whether main or minor, natural or artificial, may also be sensitive to combination with nicotine. simply by virtue of the fact that they are “active” chemicals. That’s why they act as flavorings. Such nicotine additions are often a different color from original components. The reaction (or color change) may be immediate or may take a while, particularly if the change s due to the reaction with oxidized nicotine.
Ph.D. chemist Dr. Tony Pace.
- BS Chemistry - University of Florida
- PhD Chemistry - University of Texas, Austin
- Robert A Welch Foundation Research Fellowships
- Adjunct Professor of Chemistry - Emory University, Atlanta
- Visiting Research Fellow - Georgia Institute of Technology, Chemistry Dept.
- 25 years experience in Industrial R&D with Fortune 500 companies
- Holds 3 US Patents
- Has 7 Journal Publications