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How to make a goat milk Castile bar soap

How to make a goat milk Castile bar soap

Castile soap is 100% olive oil soap, and it is mild enough to use on babies (6 months or older).  In this variant, goat milk replaces the water used to dissolve the lye crystals (NaOH).   This has several advantages:  the goat milk reduces curing time from six months to three months; the resulting soap is even gentler on the skin than regular castile, and the lather is better.


To make soap we need oils, specifically triglycerides.  We will use 100% olive oil, so the soap we get will be sodium olivate.  We also need lye, and we use NaOH for solid soap.  The lye is usually dissolved in a liquid, but here we will dissolve it in frozen goat milk.  The heat generated from dissolving the lye will quickly melt the frozen milk.


Next we need to figure how much oil, goat milk and lye to use.  You will need an accurate scale for this.   The needed quantities can be calculated from the known saponification value of olive oil, but soap calculators make this task a lot easier.  I will be using


Go to and enter the following values:




make sure you choose NaOH.  I prefer grams, and this amount (900g) fits well with my molds.  You might want to adjust it to the molds available to you.  900g is almost 2 lbs of oil, which will give you 10 – 4 oz bars.


A detailed discussion of all the information in soapcalc is beyond the scope of this short blog, but you should experiment with the site!  I reduced the water amount (increased the lye concentration) from the default value because olive oil soap stays soft a long time and we want to increase its hardness to take it out of the mold within a day or so.  Here the water will be goat milk instead.


The superfat I use is 6% (default value is 5 % and feel free to leave it that way).  Including the fat from the goat milk, this number goes to 7% in my recipe.  Superfat is the remaining left over oils that do not react with NaOH, since more oil is used on purpose.  This prevents errors introduced from saponification range uncertainties, and also, provides oils for your skin after cleansing.  Superfat makes the soap milder and more conditioning.
After you are done click on ‘print or view recipe” and you will get this screen:




The ranges shown would have you believe that the soap will remain soft and will not cleanse you at all.  Not to worry, SoapCalc has its pitfalls, castile goat milk soap will be cleansing and plenty hard after a long cure.  SoapCalc does not account for the effects of an extra long cure, which is what helps the hardness, bubbles and cleansing.


SoapCalc does a few things very well, and this is to calculate what amounts you will need. Now you know to weigh 267 g goat milk, 114 g NaOH, and 900g olive oil.


However, the goat milk needs to be frozen, because NaOH will generate a lot of heat when dissolving, and it could burn the sugars in the goat milk.  So freeze the right amount in ice cube trays.  You can keep it in bags and weigh the frozen goat milk as needed.




This is to be placed under a ventilator or extractor hood.  Leave the frozen chunks out at room temperature for a while, so there is a little liquid milk mixed into the mix.


Using gloves and eye protection, weigh 114g NaOH in a stainless steel or plastic container (no aluminum, no glass).




Pour NaOH into slushy goat milk and stir with plastic or Teflon spatula until it is all dissolved.  The mix should be creamy yellow, not brown.




Let all the lye crystals dissolve completely in the goat milk.  In the mean time, weigh the olive oil:




Stir the lye/milk mixture to make sure all the NaOH crystals are dissolved. Now we pour the lye-milk mixture into a strainer on the olive oil bowl.




The mix will be a paste since some of the fat in the goat milk saponifies before adding the mix to the oils.  Using the strainer prevents un-dissolved lye crystals from getting into the mix and it is done as a precaution.  More important here since the mix is opaque and the NaOH cannot be seen.


Using the spatula, strain the paste trough the colander.  Make sure the colander has no Aluminum components, since Al reacts with NaOH and forms a toxic gas.


Once the goat milk/NaOH mix is completely added to the olive oil, it is time to mix it.  This can be done by hand, but a stick blender will reduce the time for this task.


Inserting the stick blender at an angle can prevent trapping air bubbles.  Bubbles are harmless, just an aesthetic issue.




Now blend!  You will notice the mix turns opaque, and after a few minutes it will thicken.




Keep blending until you reach ‘trace’.  Trace is a soaping term, which means that the reaction is well under way, and it shows by the soap ‘batter’ retaining the trace of the stick blender for a short time.  Also, you can tell from the way the soap batter will start to coat the stick blender.




Do you see what I mean?  We are now ready to pour into our mold.




The Teflon spatula works very well to get all the soap batter from the silicone bowls.  After the pour, leave undisturbed at room temperature for 24 hours.  At this point it should be easy to unmold the soap.  If the soap sticks to the mold, put the mold/soap in the freezer for a few minutes.


Cut the soap into individual bars.  This can be done with a specialized soap cutter, or with a miter box and wide pastry cutter, or with a cheese wire cutter.


Now cure in a dark and ventilated place for 12 weeks.  If the soaps are stamped, do this half way during cure time.




Pine Street Products
Handcrafted soaps, lotions, massage oils, and balms. We use herbal infusions, botanical colors and essential oils. Goat milk soap uses milk from goats that have names. 

Pine Street Products (farm division) is a certified California producer. We sell organic fresh citrus, herbs, and other produce at the Altadena Farmer’s Market.

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