Soap Scraps – Salt them out!

If soap scraps need to be turned into useful soap bars, it is usually necessary to rebatch the soap. Alternatively, you can salt out the soap if it is a failed batch, or rebatching is the usual way to get it going again.

Why do we salt out soaps?

A few hundred years ago, soaps were not made with pure ingredients. They had many impurities, which were washed out by adding salt or another electrolyte. The soaps were also made by potash (K2CO3). Potash soaps are very soft, like KOH soaps. But we can exchange the electrolytes and make KOH and K2CO3 soaps harder by changing KOH soaps to NaOH soaps. But salting out soaps cannot change all KOH to NaOH; there will always be KOH left (1/3 to 1/2 of the soap). This is the reason why these soaps give more lather.

Salting out the soap is more time-consuming than rebatching, however, unlike rebatching, it is capable of removing many additives, including color and fragrance, from the soap.

Salting out will remove the majority of the natural glycerin found in handcrafted soap, depending on the type of additives and the depth of color. The amount removed depends on the type and depth of color.

Rather than mixing and simmering the soap in plain water, it can be more efficient to use a weak lye solution. Of course, NaOH can be added to the salt solution to save time.

After the soap scraps have been salted out, what you can expect is that the essentials of the soap (the salt of fatty acids) will remain intact.

Best practice to salt out soaps

  • Grate the soap as finely as possible.
    If necessary, use a salad shooter, food processor, or hand grater to grate the soap into fine shreds, in case the soap is too thick. When weighing ingredients for a recipe, it isn’t necessary to be very precise because perfection is unnecessary. You just need to be close enough to get accurate results.
  • Use about twice as much water as the weight of the soap. You may need more water, depending on the soap you have.
    I recommend using distilled water, deionized water, reverse osmosis water, or even rainwater if possible. Using tap or spring water that has hard water minerals in it can adversely affect the quality of the finished soap.
  • Temperatures above 70°C (158°F).
  • Use a wide but low pot. The narrower and higher the pot, the longer the process.
  • Never add water without electrolytes.
  • Use a very fluid soap/water mix. When you throw a bit with a spatula in the air, the resulting soap bubbles should be small, clear, and stay intact until they hit a surface. Use between 3 parts water to 5.5 parts water for 10 parts soap.
  • Use 0.3% – 0.5% excess of alkali (use a lye calc and calculate the lye for minus 0.3% superfat).
  • Use a ~10% electrolyte solution, starting with 1% (1 part electrolyte to 99 parts distilled water).
    Add more electrolytes in small steps until the soap starts to separate. The lower the molecular weight of the soap, the harder it is to salt out. Soaps made from highly unsaturated fatty acids are more difficult to salt out. Laureate, for example, requires a saturated salt solution.

When soap is salted out, it goes through several steps:

  • It foams a lot after adding salt and moderate temperature and can easily rise above the rim of the pot. When the soap is cooked longer, it is still liquid but becomes thicker and more viscous.
  • You can see the slurry slide over the wet spatula in flat lumps or flakes. As the salt solution draws water from the soap during prolonged boiling, it becomes thicker and thicker. The salt water collects at the bottom of the pot. The soap throws larger and larger foam bubbles as it boils, and the steam can only escape through very small holes. This produces noises that sound like talking, blowing, or whistling.
  • The surface of the soap is torn into plates. They are pushed over each other by the steam and look dry. When the soap and salt are in equilibrium in terms of their attraction, the soap sinks down, and the foam disintegrates into delineated grains. The soap now has the lowest water content it can have. Now it has become curd soap. It no longer rises even under the greatest heat. The salt solution no longer extracts water from the soap. At this point, it is uniform, and the steam escapes intermittently with violent bubbling. The boiling is finished.
  • Now remove the soap from the pot. The softness corresponds to the respective water content. When you rub a sample between your fingers, it must feel dry, smooth, and not crumbly. If the sample is not soft, you have made a mistake in salting it out and used too much salt. You can start over and dissolve the soap in water and let it boil until the consistency is right. The soap will now take three to ten days to set.
  • You can use a saturated brine solution or add it spoon after spoon. Cook the solution or keep it at low temperature. There are lots of very complicated ways to calculate the heat, the amount of water, soap, and water. But as I don't want to spend my time calculating, I would rather try it myself.
  • If you used too much salt, you can wash the soap. Grate it, add water, let the soap separate from the salt liquid, … You know the rest. 🙂

Important:

Be sure to use proper safety gear and follow safe working procedures when dealing with lye. Even a weak solution of lye can cause dangerous burns, and if splashed on the skin, it can have long-term effects.

Cooking soap

Conclusion

Professor Blue

The method of salting out soap scraps provides an effective way to reuse unused soap remnants and transform them into useful soap bars. While it may be more time-consuming than other methods such as rebatching, salting out offers the advantage of removing many additives like color and fragrance from the soap. It’s important to note that the salting out process offers various variations and options, including the choice of electrolyte and controlling the temperature, to achieve the desired properties of the resulting soap.

Salting out allows for the creation of soaps with different hardness, foaming properties, and textures to meet individual needs and preferences. However, adhering to best practices and safety precautions is essential, especially when handling lye, to avoid injuries.

Overall, salting out soap scraps provides an environmentally friendly way to recycle excess soap remnants and produce high-quality soap products while minimizing the use of chemicals and resources. With knowledge of the right techniques and safety measures, this process can be successfully executed to yield soaps of high quality and utility.

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