You are not the first producer or the only one to have maple syrup taste buttery. Professional taste testers sometimes note a buttery taste. As long as you don't use butter as a defoamer (that was one of the older ways to control foam) the buttery taste is OK. I would not worry about it. There are other numerous tastes associated with pure maple syrup too. You can read about that in The North American Maple Syrup Producer's Manual.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.