I've read in a number of threads here on ECF that, given proper conditions (cool and dark) two years could be expected.
You can see the degradation in 100mg per ml over time as it discolors. It starts turning brownish- which is a sign of oxidation.
I saw that discoloration first hand, for the first time, this evening.
I purchased two bottles of 100mg unflavored more than a year ago, both from the same purchase & supplier. They've been stored together under identical conditions, excepting one of the bottle's seal had been broken to use some of the liquid ... that was perhaps nine months ago.
I finally got around to obtaining more bottles and base liquid to cut the 100mg down. When doing so the difference was unmistakable. The bottle with the unbroken seal was still clear as water. The opened bottle was markedly darker. I'm a bit color deficient, so I'll take your word for it that it is brown ... although I was thinking more yellowish.
My question is, does that coloration mean the liquid no longer effectively is 100mg? Or does it mean the taste will be off? Or is it only a matter of color insofar as the usability of the liquid is concerned?