Nicotine is the only tobacco flavor that I use. And, for that reason, I have always said that "unflavored" is the best tobacco flavor.
So don't worry about a small amount of taste. If it has become "peppered", then there is an oxidation problem.
ps: The nicotine that I'm vaping right now is 8 years old, and this 1 ltr. bottle should last another 2 years before it's all gone.