I love milk soaps, they are mild and gentle and evoke a feeling of warmth, natural goodness and country charm. If left to their own devices milk soaps will always gel, the sugar in the milk will raise the temperature considerably, so if you don't want your soap to gel then you have to take pretty drastic measures.
Now why would you want to stop your milk soap from gelling? Does gelling make a difference to the quality of the soap? No, the quality of the soap doesnt change, but what does change is the colour and that might be important to you.
When you let a milk soap gel, it generally turns a deep tan colour. If you have also added honey, you might find that it goes even darker.
These two soaps are from the very same batch, the one one the left is the main batch, gelled in a wooden log mould, the one on the right was leftover soap in a small individual mould, and ungelled. As you can see, the gelled soap is much darker than the soap which didnt gel.
This is what I do when I make milk soaps -
I use 35/40 water and 65/60 milk for my liquid. I use the water to mix up the lye. You will need to stir for longer than normal to dissolve all that lye in such a small amount of water, but it does work. I add the cold milk to the oils when the hard oils have melted, and stickblend it in thoroughly. If I am using a scent for the soap, I also add that to the oils and milk mix. I then add the cooled lye water, stickblend until it reaches thin trace and add whatever botanicals I want to use ( for example poppy seeds, wheatbran, oatmeal ) and perhaps a bit of honey. Handstir until the botanicals are well incorporated.
When making milk soaps I soap much cooler than I would normally do. I take the oils of the heat as soon as there are only a few bits of hard oils left, they will still melt because of the heat of the liquid oils. Adding the cold milk cools the oils down really quickly. The lye water I prepare well before I start melting the oils and put it into a bowl of very cold water to cool it down quickly. I usually aim for no more than 80F or even room temperature, especially when adding honey to the soap as well.
I never use a log mould for milk soaps these days. I used one for my first goats milk and honey soap, and insulated it as well, and it went crazy! It rose like a loaf of bread, and cracked right down the middle. I had to squash it all down again and somehow it ended up a really nice soap anyway. I now use slab moulds for milk soaps ( actually a lovely old wooden tray found at a boot sale for 50 pence ). As soon as the soap is poured, I stick it in the freezer, sometimes for a few hours, or, if I made the soap in the evening, overnight. Take it out of the freezer, and voila, beautifully creamy looking goatsmilk soap! It is easy to remove from the mould when you take it out of the freezer. I just let the slab sit for a while to return to normal temperature and then cut to required size.
This is a very plain goats milk soap without any additives, no fragrances, no colours, which makes it very suitable for young and/or sensitive skin.
There you have it, using milk in your soaps should be quite straight forward. Having said that, of course, nothing is ever straight forward, lol, and the strangest things can happen. For example, one lady in the States made a milk soap, put the mould outside in the snow, and it still gelled! Another put the soap in the fridge for a few hours, took it out and it started gelling, lol. So you just never can tell with 100% certainty that things will work as planned, but if you follow the above, then at least you should stand a pretty good chance!