ED, I was curious about it. set refraction in the shader to 1.33(not sure exactly how I got to the I.R. setting. I was just playing around - I'll have to do it again if you need to know) and it didn't duplicate the problem. is your glass about 1.6 and your water(ginger ale) about 1.3? looking in the ginger ale in your render the refaction appears to be ok so it might either be the tumbler's I.R. is off. As ewinemiller duplicated the bug this might not help but any time someone mentions refraction or spirals, I gotta fool around with it, anyway. - TJ