are you water processing ? are you using margerine, this has happend to me, sort of blackened, with both. junk the margerine. no good for you either. with water processed butter, you often need to do a second step to remove the brown, now ucky water that sometimes does not compleatly seperate from the water after the original processing. if that is the case, slowly on very low temp [as you know] re-melt your butter, let it cool down again/refrigerate. if you do this in a glass container you will be able to see brow water at the bottom of the container/jar. slide it out, or poke 2 holes in it 1 for air, 1 for drining brown water. . let me know if this is youe problem and if this info helps.

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Penelope