I recently have started mixing together my own products and in the midst of my research I have come across some pretty scary articles about harmful bacteria, mold, and yeast growing in mixes that aren't properly preserved. I've seen that the solution is to make small batches and use them quickly, but I don't know if I can make it through my mixes in two or three weeks.

So my questions are... Have you ever had any mixes spoil? If so, is it very noticiable (i.e. drastic change in scent or color)? Have any of your mixes ever made you sick?