I decided that I was going to freeze the milk first. Which was great, because I already had some soy milk in the freezer. It had been there a while and was a little freezer burned, but I tried it anyway. This was just an experiment, after all. I also had an ice bath ready to keep the temperature down when making the lye solution. Turns out I didn't really need the ice bath for the milk. Just by sprinkling the lye in slowly, I was able to keep the temperature where I wanted it. The oils were too hot when I was ready to soap. So, I used the ice bath in the end to cool them quickly. I didn't want this soap to gel, so I placed the mold in the refrigerator overnight.
The whole process was a little easier than I thought it would be - which was a pleasant surprise. I'm definitely encouraged to experiment a little further by adding scents/colors to the milk soap. I'd like to use fresh milk next time too!
I sliced this soap after only 24 hours and it was still a little soft. I think milk soap processes slower than soap made with water. So, next time I would probably wait a little longer. Overall, though, it was a great success! I can't wait to keep soaping!