My special Redneck soap made with beer
Firstly, you absolutely must let the beer go flat. Open it up a couple days ahead of time. Once I just opened the tab top a little, but even after two days, the lye started to volcano the beer/water solution. So last time, I opened the beer can and poured the beer into a bowl, and left it for three days, and this worked with no problem. Some beer soaps contain only beer as their water portion, but I thought that would bring the price up to high, so I simply replace a portion of the water with beer.
When to add beer to the soap varies as well. In the past, I would have the beer in with the water, then add the lye. But after the lye/water started foaming, and I decided to rethink this, and decided to add the beer to the oils just after I add the lye/water to the oils. This has been the best solution in trying to avoid the possibility of having your lye/beer/water solution volcano out of your container.