Both times that I've tried to make aioli/mayo, it comes out bitter. My first thought, of course, was that my oil might be rancid. I've tried them with olive (which was most definitely not rancid...I use it too fast) and vegetable oil. I thought the next culprit could be the garlic, but I try to make sure that what I use is very fresh.
Any other ideas? What am I missing?