I've been mixing the concentrated Similac Sensitive and keeping the pitcher in the fridge until we use it all by the end of the day. I've checked over and over to make sure I'm mixing it right (1:1), checked our bottles for dishwasher residue, etc. DD especially seems to turn her nose up at it a lot, especially as soon as it gets lukewarm or cold. This stuff just smells foul, more so then the Similac Advance or Goodstart. I'd taste it, but it all makes me gag anyway!