How to Make Milk Soap: Tips to Try
You Can Use Any Kind of Milk for a Moisturizing Cold Process Soap Recipe
Reading Time: 6 minutes
Learning how to make milk soap provides another use for that excess goat milk. It’s not as hard as you’ve probably heard!
It’s a popular misconception that making soap with milk is difficult. The truth is, all you need is a little patience and careful attention to directions to make using milk a fun and creatively satisfying soap-making experience. And remember that most soapy “mistakes” can be reworked into perfectly usable soap, so don’t let fear of the unknown hold you back from trying something new.
The list of dairy and non-dairy milk that can be used for making soap is long and varied, and the procedures below will work for all the many different types when learning how to make milk soap. For example, goat’s milk is a current popular choice, and produces a creamy, moisturizing soap with small bubbles, while soy milk also produces a dense, creamy lather. In my soaps, I use coconut milk, which makes piles of resilient, creamy, medium-sized bubbles. Milk from sheep, donkeys, horses, yaks, and other mammals all work the same way in soap as goat’s milk, and contain the same basic ingredients: water, sugars, and proteins, which are also the same basic soap ingredients found in the vegetable-sourced alternatives like coconut, soy, rice, and almond milks. You can choose from the entire range of cow’s milk, from skim to whole to heavy cream and buttermilk, too, depending on the type of soap you’re working to create.
Three of the most common methods for using milk in soap making are the “Milk In Lye” method, the “Milk In Oils” method, and the “Powdered Milk” method. Each process creates a great soap, so chose the method that fits best with your own personal preferences.
As with any soap making recipe, be absolutely sure to use all the proper precautions in handling the lye for soap. If you’re already experienced in adding lye to water, you are aware of the superheating process that takes place, which can raise the temperature of the solution as high as 200 degrees Fahrenheit. But be aware that liquids other than water can and do react differently, and nowhere is this more true than soaping with milk. Both animal and vegetable-sourced milks contain an abundance of natural sugars, and as the lye solution heats up, those sugars can burn, producing a burnt sugar smell as well as turning the soap brown, or creating a soap with brown specks. If your goal is a pure white soap, you’ll need to follow these procedures carefully to achieve that. (Of course, a browned soap is still useful, and the burnt sugar smell dissipates quickly, leaving no bad odors behind.)
A tip about water discounts: water discounting means using less water than your recipe calls for. When using milk, you discount water and replace it weight-for-weight with milk. Another reason for discounting water is making soap that dries faster, but please note that soap drying and soap curing are two different processes. While a soap may harden (dry) faster than six weeks due to water discounting, it’s still not fully cured until it’s no longer losing weight.
For the “Milk In Lye” method, milk is used in place of some or all of the water in the lye solution. This method requires advance planning due to the necessity of pre-measuring and freezing the milk. Care must be taken to ensure that the lye dissolves fully into the cold liquid, as it tends to stick together in clumps in an ice-cold liquid solution. To ensure that the lye fully dissolves, use a small portion of water to fully dissolve the lye, stirring until the solution is clear. This will cause the solution to superheat, so next, set your bowl over an ice water bath to quickly cool the lye solution. Once cold, add the frozen milk and allow to dissolve slowly into the lye solution. The goal is to keep the temperature as low as possible, and definitely below 100 degrees Fahrenheit, which will prevent discoloration.
The “Milk In Oils” method involves using a water discount in the lye solution and later adding the remainder of the liquid (as milk) either to the melted oils, to the soap batter during emulsification, or after trace when the batter begins to thicken. The benefit of adding the milk to your melted oils or your emulsified soap batter is simplicity. The benefit of adding milk at trace is that it thins out the soap and gives you time for creative effects, such as mixing in fragrances or colors or using advanced pouring soapmaking techniques. You can work at your normal soaping temperatures if browning is not an issue. If you prefer a whiter result, try soaping with cold lye solution and oils. Using an ice bath to chill both mixtures is also effective.
Last, the “Powdered Milk” method involves adding powdered animal or vegetable milk. This can be done at any point in the process and does not require discounting the water to make up for the added liquid volume. Simply follow the mixing directions on the package, measuring the milk powder to correspond to the amount of water in your recipe. If adding the powdered milk to the lye solution, be sure that the lye is fully dissolved and the solution has been thoroughly chilled before adding the milk. Some heating may occur due to the sugars in the milk powder, so be prepared with an ice bath in case you need to cool the lye solution again. It’s less likely that a heating reaction will occur if the milk powder is added to the finished soap batter at emulsification, but soaping at a cool temperature is still recommended to avoid discoloration.
Once the soap is poured into the mold, it should be placed directly into the freezer to prevent discoloration from overheating. Heat in the finished soap can also create a gel state, which is harmless and won’t damage your soap. A fully gelled soap will be slightly darker in color and have a translucent quality, unlike soap finished in the freezer, which will be opaque.
For best results, use a tried-and-true fragrance oil that does not discolor, accelerate trace, or cause the temperature of the soap to rise. If you are aiming for a white soap, be sure that your fragrance does not contain vanillin, which causes browning. If using essential oils, take note that florals, citrus, and spice oils can all accelerate trace and cause heating.
Although there is fat in most milk, the amount is negligible and doesn’t need to be considered in formulating your recipe. An average superfat percentage is between one and seven percent, depending on whether the purpose of the soap is household cleaning or bathing. Some soaps can contain upwards of 20 percent superfat for an extra gentle, extra moisturizing facial bar. The higher superfat percentages require longer curing times to produce a hard, long-lasting bar, however, so take that into account when scheduling your Christmas soap making marathon.
Some people find that adding sugar to their soaps increases the lathering quality, but when using milk you’re already adding the sugars contained in the milk, so adding more is unnecessary. Salt is often added to increase the hardness and longevity of a bar of soap, and while salt can successfully be added to a milk bar, keep the amounts small — 1 tablespoon per pound of oils is typical to avoid a reduction in the lathering quality.
If you’re creating a milk and honey soap, or an oatmeal, milk, and honey soap, bear in mind that the sugars in honey can burn just like the sugars in milk, producing discoloration and non-persistent odor in the finished product. It’s best to use honey sparingly – about ½ ounce per pound of oils — and to ensure that your soap batter is cold when adding the honey. It’s generally best to add honey at a thin trace — beyond the initial oil-and-water emulsification stage, but before thickening begins in earnest. Keep a careful eye out while mixing, and be prepared to throw it into the mold quickly if it should threaten to thicken up. Honey is also likely to cause superheating, so again you will need to place the soap directly into the freezer once molded to prevent the gel stage from occurring.
When it comes to learning how to make milk soap, there are near-endless options and combinations. With a little planning and these tips in mind, you should be well prepared to tackle your first batch of skin-loving milk soap full of creamy, healthy, moisturizing goodness.
Melanie Teegarden is a longtime professional soapmaker. She markets her products on Facebook (https://www.facebook.com/AlthaeaSoaps/) and her Althaea Soaps website (https://squareup.com/market/althaea-soaps).
Originally published in the May/June 2018 issue of Goat Journal and regularly vetted for accuracy.