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February 11, 2015

Making Soap with Goat Milk: Cold Process

How to make soap with goat milk using the cold process method.

I've been making goat milk soap for almost ten years so it's second nature to me now, but I remember how scary it was the first time I made it.

If you haven't yet read my first post in which I talk about lye safety, soapmaking equipment, and how I get ready to make soap, I hope you'll go read it first.

Once again, let's get the legal stuff out of the way first:

These are the safety procedures I use.
Please note that I am not responsible for accidents;
this post is for educational purposes only.

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In Part One I weighed the oils I'll use in my soap, weighed the frozen milk, and lined my silicon mold (affiliate link) with freezer paper so it will be easy to get the finished soap out. Usually I do this a day or two before I actually make the soap. I have small pockets of time in my day, so I've learned to break soapmaking into two sessions.

There are two methods of making soap, called "cold process" and "hot process." Both processes begin the same, and that's the part we'll do today - this is how I make cold process soap.

Before I use a new recipe or change a recipe I always run it through a lye calculator. I type in the amounts of the oils I'm using, the amount of liquid, and the calculator tells me how much lye to use. My favorite lye calculator is at Brambleberry, but there are others online as well. Don't skip this step when you make a new recipe, typos happen! Also, if I need 10 ounces of coconut oil but only have 9, I can substitute an ounce of another oil BUT I use the lye calculator to see if I need to change the amount of lye.

I take the containers of oils out of the refrigerator or freezer and let them warm up a bit. I cover the counter with newspaper to protect the surface. I get out my tools: mixing spoons, immersion blender (affiliate link), and plastic mixing bowls. I also get the zipper bag of weighed milk out of the freezer and the lye out of the cupboard.

My rule is to not make soap with children or pets in the room, and to focus only on my soapmaking. I don't have children at home anymore, but I do have dogs and cats in the house. The dogs go in their crates and the cats are "put in time out" in another room. I don't answer my phone if it rings or buzzes or makes any other notification noise.

How to make soap with goat milk using the cold process method. Here is the equipment you'll need.

I don an apron and my goggles, rubber gloves and mask (affiliate links). Hubby says I look like a mad scientist.

Weigh the lye

Next I weigh the amount of lye I'll need. I weigh it in an old margarine tub that is well-labeled, and set it next to the sink with the lid on.

Warm the oils

Remember when I said in my first post that I weigh the liquid oils into one container and the solids such as tallow, lard and coconut oil into another? Do you also remember I said that lye burns the milk sugar and turns the soap brown? This is why I use frozen milk and why I keep the two kinds of oil separate: to keep things as cool as possible: to keep the browning to a minimum.

How to make soap with goat milk using the cold process method.

I warm up the solid oils and butters in a saucepan until they melt and liquify, then pour them in the larger of my mixing bowls. I add the room temperature oils (olive oil, etc) to the melted oils. The room temperature oils help to cool the heated oils a bit. I pour this whole mixture into the dishpan in my sink.

Add the lye to the milk

The frozen milk goes into my smaller mixing bowl and I sprinkle the lye on top, then put the lid back on the tub the lye was in and set it aside.

How to make soap with goat milk using the cold process method.

One book I read called this "snow on the mountain." The author uses the phrase to remind her to add the lye TO the milk, like sprinkling "snow" (the lye) on the "mountain" (the liquid, or in this case, frozen milk). Adding liquid to lye will cause an eruption of caustic lye that can be very dangerous.

How to make soap with goat milk using the cold process method.

Using my mixing spoon I carefully stir the lye and frozen chunks of milk. The heat of the lye will melt the milk. Keep stirring until all of the frozen milk has melted. I love these old Rubbermaid bowls with pour spouts because I can hold onto the handle while stirring; I found them at a thrift store.

Add the lye/milk to the oil

I slowly add the lye/milk mixture into the oils, stirring as I go. (Again, add the lye mixture TO the oils.) Stir gently so the lye mixture doesn't splash around.

How to make soap with goat milk using the cold process method.

If I were making a water-based soap, the directions would say to let the lye/water and the oils cool to the same temperature before combining. Because I'm using milk, I skip that step and add the lye/milk to the oils regardless of their differing temperatures.


... and stir and stir and stir. Using an immersion blender helps this step go a bit faster.

How to make soap with goat milk using the cold process method.

I alternate between using the stick blender and stirring with my mixing spoon. I don't want to burn out the motor on the blender. I'm careful to keep the blender submerged when it's turned on so the raw soap doesn't splash or spurt.

How to make soap with goat milk using the cold process method.

Bring the mixture to "trace"

The goal is to bring the mixture to "trace". Eventually you'll notice that the color has changed, instead of being transparent it changed to translucent and then became opaque. It will begin to thicken after awhile. "Trace" is kind of hard to explain. Let's see, it's thick enough that when you pick up the spoon, the liquid soap that falls off doesn't immediately disappear into the rest, it sort of sits on top of the surface. Or you can drag the spoon through the soap and a line will remain visible.

How long does it take for the soap to reach trace? It's different every time, and it depends on the room temperature as well as the temperature of the ingredients and even on the type of oils you are using. Just keep stirring and blending until it's thick.

How thick? I tend to reach a thick or rather heavy trace. Some soapmakers like a light trace that is much thinner than mine. There's a bit of leeway here. It's easier to tell a heavy trace from a light trace.

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This is where cold process and hot process part ways.

I prefer cold process soap. It looks smoother when it's finished and the color is lighter. Hot processed raw soap is much thicker; the difference is like cake batter (cold process) and a stiff mashed potato consistency (hot process). I think the cold process method is much easier too, but hot process is quite popular, probably because the curing time isn't as long.

This batch is cold process, so at this point I simply pour the soap into my mold, use my mixing spoon to scrape out the dishpan, cover the mold with a piece of paper to keep dust out, and walk away. I leave it undisturbed for 24-48 hours, then unmold it and let it set for another 24 hours or so before cutting. I do this in the mudroom, where I can close the door and not worry about the cats getting into the raw soap on my workbench or dog hair landing in it.

Clean up

Because I don't have small children anymore, I just put all my soap-covered utensils and bowls and tools (my immersion blender comes apart so I can put the electrical part away) into the dishpan while still wearing my protective goggles and gloves, stick the whole thing in a garbage bag, twist it closed and clip it with a clothespin or binder clip. I set it on the highest shelf in the mudroom, and leave it until the next day. By then, the soap has completely saponified and it isn't caustic anymore - it's soap instead of caustic lye and oils and milk.

Then I put it all in the kitchen sink, fill the dishpan with water and let it all soak for a bit, then I wash everything. I don't have to wear rubber gloves at this point.

If you have children at home, you'd probably want to clean it all up instead of leaving it on a shelf unwashed. I'll let you research the best way to do that since I haven't done it myself. Be sure you're still wearing your rubber gloves when you clean up.

How to make soap with goat milk using the cold process method.

We'll unmold, cut and cure the soap in another post, but here's a sneak peek at my finished cold process bars.

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In this series:
Soapmaking: Safety, Equipment, and Getting Ready
Soapmaking: Cold Process
Soapmaking: Hot Process
Soapmaking: Unmolding, Cutting and Curing
Soapmaking: Random Thoughts and a Recipe

If you've ever used goat milk soap, you know how luxurious it is. Here's how to make your own using the cold process method.

This post has been shared at some of my favorite blog hops.


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  1. Thank you, Kathi! Reading your soap making posts have become part of my research.


  2. Kathi at Oak Hill Homestead7:44 PM

    I hope it helps, Fern.

  3. I didn't realize the work that goes into soap making! What a loving and rewarding art!

  4. Kathi at Oak Hill Homestead6:31 AM

    Hi AnnMarie - it's funny, getting ready to make the soap takes a lot longer than the actual making of it. Thank you for your comment.

  5. Hi Kathi, I had a couple of questions. I've used goat milk soap that is soft and disappears quickly and some that is harder and lasts a lot longer. Does the tracing or the hot/cold process have anything to do with the lasting power of the soap? (Obviously, I don't know the language to soap making at all. But I'll need to learn next year when we finally start milking our goats.) Thanks for the tutorial, I'm pinning for next year!

  6. Kathi at Oak Hill Homestead7:44 AM

    Hi Jennifer. Those are great questions! I'll go into some of them more in Part Four (I started writing about soap and just couldn't stop!)

    How long soap lasts depends on several things. While some soapmakers make vegan soaps using only plant-based oils, I use beef tallow in my soaps which makes a harder soap. Also, the longer you let soap cure after making it the harder it will be and the longer it will last. And finally, be sure to keep your soap dry - don't let it sit in a puddle of water between uses.

    I haven't noticed if there's a difference in how well hot vs cold process soap lasts. I don't usually make hot process so I don't have enough experience to know. It's an interesting question.

    Hope you have a great weekend.

  7. Thanks Kathi! I'll be looking for your next two parts. I can't wait to start making my own soap.

  8. Kathi at Oak Hill Homestead6:13 PM

    You're very welcome, Jennifer.

  9. Thanks for this great post, it has made me want to make milk soap very soon. I can't wait to see the next installment. Thanks for sharing at Good Morning Mondays. Blessings

  10. Kathy, great post.
    I was wondering about your mold. The Milk soap making book I have stated that loaf molds do not work well with milk soaps, but obviously, you have had success with the loaf molds.
    Good to know.

  11. Kathi at Oak Hill Homestead6:05 AM

    How interesting, Sandra. I'm glad I didn't read that before I started; I probably wouldn't have tried it. Loaf molds work just fine. Perhaps using what I call a sheet mold (a big square mold) would keep the soap cooler and help preserve the color? The only problem I've had is with hot process soap if I don't get all the air bubbles out because it's so thick. I ended up with holes in my soap more than once.

  12. Again, you have taught me something new! I wish I could spend a week following you around, learning soap making (and everything else you do!) Thank you so much for sharing at the (mis)Adventures Monday Blog Hop.

  13. Kathi at Oak Hill Homestead10:17 PM

    Wow, I'd love to have some help. You're welcome any time! :-) Thank you!

  14. Hi Kathi, thanks for this super-helpful tutorial on making goat's milk soap (cold process). I've tried making goats milk soap before, but with less then satisfactory results. Your tutorial made it super-easy, leaving the goats' milk frozen. Plus,I like how you did the stirring in the sink. I felt more secure doing it that way then on the stove.
    I just used your tutorial and made a 2 pound loaf - it is now beginning it's cure out in the garage.
    Aaa and, I am going to use my husband's miter box to slice the soap when it is ready-- as you mentioned in your post. What a great idea! I have never been able to slice a straight line :-)

  15. Kathi at Oak Hill Homestead12:49 PM

    Yay, Mary!!!! You did it! I'm glad there were a couple of good tips in there that you found helpful. The miter box makes cutting so easy. Woohoo on your first successful batch!!

    (I like stirring it in the sink because, not only is it more secure and I don't have to worry so much about spills or splatters, it's the right height for me.)

  16. Thank you for all the information! One quick question, at what temp to the oils need to be before adding the lye?

    1. That's a good question, Lena. Most sources will tell you to wait until the oils and the lye/liquid are the same temperature. And while it's important to follow all the soapmaking rules, it's different when you use milk as your liquid.

      I use frozen milk so that the lye won't burn the sugar in the milk and turn my soap orange or deep brown. The person who taught me this always mixed her oils with the lye/liquid as soon as the lye had warmed up the frozen liquid and there were no visible frozen lumps left, so that's how I've always done it: as soon as the lye and milk are completely mixed, I add it to the oils.


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