I attempted to create glycerin today using some "suspect" lye (a brown powder produced from potash rather than a white one from the store) and some beef tallow.
I melted the tallow in a pot, and mixed in double that volume of water, in which I had dissolved a half mole of lye. A white fluffy-looking layer immediately formed on top of the mixture, which I suspected might be a soft soap. But when I tested it, it was still very greasy, and very alkaline.
I set the whole mixture aside and let it cool. This took a surprisingly long time. (I think the alkali was still doing its thing and generating heat) After a bit I put it in the fridge to accelerate the cooling. Later I returned to find no glycerin layer at all, and a strongly alkaline and greasy layer where I had expected to find soap. I mixed in enough vinegar to neutralize the mixture, and set it aside to settle again. Two hours later there were still only two layers, when I had been expecting three.
I suspect I either used an inappropriate amount of lye, or that the lye was contaminated.