In my thread on “Homogenizers, how and why they work” I called on longtime members and suggested a comprehensive data based discussion on exactly what “steeping” is. Other than showing how a mix can be determined to be at its final and stable stage, I wont offer much unless asked.(Already covered)
As to high tech testing by gas chromatography or mass spec analysis etc, suffice to say that these expensive tests are useless unless a homogeneous sample is taken.
Steeping might involve homogenization as a major part, but a huge component of it, guaranteed, is reactions of the flavoring chemicals with each other. These reactions are affected by nicotine, most likely because it is basic. They’re also affected by water, because it is both a proton and hydroxyl donor. The only scientific study I know of where they actually analyzed changes in chemicals formed during steeping is this one.
https://www.sciencedirect.com/science/article/pii/S0278691519305174
They were only interested in analyzing diacetyl/acetoin/acetyl propionyl degradation and conversion (because it was prompted by the scare over those chemicals, obviously). The study is free to read and clearly shows major changes in the concentrations over time, affected considerably by both water and nicotine.
I can also say for certain that three common types of flavor chemicals, esters, acids, and alcohols, will react in the solution. Esters can swap the acid components with each other, and de-esterify into their alcohol and acid components. Acids can react with alcohols to form new esters. And acids can “swap” with the acid component of an ester, freeing the ester’s acid into the solution and forming a new ester. Likewise, an alcohol can pick up the acid from an ester, leaving a new alcohol and a new ester.
For example, you can have ethyl acetate and butyric acid in your juice. These can change to ethyl butyrate and acetic acid, and they can go back again. It will be an equilibrium between all the chemicals.
Things like aldehydes and alkenes (flavor chemicals that contain a double carbon-carbon bond) are prone to oxidation over time. They usually don’t return to their original form like ester/alcohol/acid reactions can.
All this is happening constantly in the solution over time.
Thanks for posting. @woftam and I have had many discussions regarding this study. I have always considered it mostly fear porn but have steadfastly advised that regardless of mixing method, nicotine and oxidation are to be avoided. For example, on numerous occasions I have pointed to FLV’s recipe book that states clearly that what many define as “steeping” is actually undesirable oxidation. Combine this with the words of FA’s founder about the properties of VG and why they don’t make VG based concentrates I think makes a strong case. Can I be wrong, absolutely. However I have nearly 5 years of successfully producing stable mixes.
This topic came from IMO, an all too common statement that “After 3 years of DIY and trying all kind of steeping methods, still couldn’t get the ‘premium’ quality.”
Once again I am not a chemist/ flavorist and I suspect that 99.99% of all others here are not. Establishing a viable method to help people is the goal.