Hello Goatgirl,
Usually milk and such additives are added in a rebatching step to avoid overheating and other problems that usually emerge from sugars and proteins found in milk.
If you wish to try adding the milk from the beginning you can approach it in one of two ways:
- Cool the milk in a fridge for a couple of hours, then put it in a bowl of ice, and add the lye very slowly to the desired concentration. You might consider adding the lye in steps and cooling the solution in the fridge between the addition. The goal is to avoid the heating from the lye dissolution and reduce changes in color and smell. (note that this way it can get very bad very fast, so be extremely careful during preparation)
- prepare a concentrated lye solution (1:1 water:lye). Wait for it to cool down to room temp then dilute with goat milk to the desired lye concentration. this technique is less risky from a preparation point of view.