E85: E70, E74, E80...changing pump mixture a problem for tuning?

[Halon]

That is one of the downfalls of E85, is that it goes through I believe 4 different blends over the course of a year. Some people seem to be buying barrels of E98 and just running that since it has a higher ethanol content, and a steady mixture. I'd really like to be able to test what is coming out of the pump though. Maybe I'd buy a barrel of E98, and if I could just test the mix coming out of the tank, and add a little E98 to the tank if the E85 is on the lower mix to bring it back up to the 85%. But as of now, I haven't found a quick and easy way to test it.