What is cold process soap?

Image Credit: 
Main Image: 
Image of cold pressed soap

The most popular, and oldest form of soap making process is the “Cold process method”, where fats such as olive oil react with lye. In both hot and cold process soap making, heat is required for saponification. The cold process soap making takes place at sufficient temperatures to liquefy the fat being used. Cold process soap making requires exact measurements of lye (sodium hydroxide) and fat contents by using saponification chart to ensure that the finished product is mild and skin-friendly. This process should be made with precise weights and measurements to ensure an accurate lye/water/oil ratio. The soap formed through this process has a nice texture, lather, and good quality.

Cold pressed soap is a soap made by using an external heat source to speed up the saponification process. A simple handmade soap gives you the feeling of being pampered at a spa. The emergence of soap remains a mystery but legend has it that ancient site at Mount Sapo in Rome was famous for animal sacrifices, the residual fat and ash got collected under ceremonial altars. One day heavy rain made fat and ash to mix with rain and that flowed down to the slopes to the banks of rivers where washer man were washing their clothes and this mixture made the clothes clean.

The basic formula for making soap: Fatty acid(oil) + Base (lye) = “A salt”(Soap)

What are the Ingredients used?

  • Lye: Make sure it is 100% sodium hydroxide
  • Oils: Can use Olive, coconut, palm, sunflower, vegetable, lard, Crisco oils but coconut oil gives good lather
  • Distilled water: Use of distilled water minimizes minerals in the soap
  • Fragrance: Sandalwood, rose, jasmine etc
  • Colorant: optional


How to prepare soap by Cold process method?

  • The first step is to check the exact amounts of fat on saponification chart, which is used to calculate the exact amounts of lye
  • Excess unreacted lye in the soap will result in high pH which means it is more alkaline and can irritate the skin.
  • Pour the lye  into water and stir continuously until lye is dissolved in water;  oils are heated and melted if they are solids at room temperatures
  • Cool both the substances to approximately 100-110o F and no more than 10o F apart, they may be combined.
  • This lye-fat mixture is stirred until trace (It is the point where soap is done enough to pour). When you reach trace, slight ripples will form on the surface and remain there. There are varying levels of trace
  • Depending on how the additives will affect trace, light or medium or heavy trace
  • After much stirring, the mixture turns to thick gravy or thin pudding
  • Just before the mixture gets thick add fragrance oils, botanicals, herbs, oatmeal, additives and other essential oils at light trace
  • It is poured into molds and kept warm with towels and left to saponify for about 18-48hrs
  • The soap will go through the gel phase, where the opaque soap will turn transparent and again turns back to opaque
  • After insulation it becomes difficult to remove the hard soap from molds and cut into bars.
  • Cold process soaps are cured and hardened on a drying rack for 2-6 weeks before use.
  • Cold process soaps can be later chopped up and remelted and can be made into hand milled soaps.


What are the other types of soap making process?

  • Melt and pour: Clear soap base is melted, colored and mixed with fragrance, and placed into molds
  • Hand milled: It is a cross between cold process soap making or hot process soap making and melt and pour soap making. It is also known as “rebatching soap”. Grate the soap base and heat it in a kettle with some water added to it. When the mixture melts down to a mushy mess add colorant and fragrance. This method is often used to preserve the fragrance or healing properties of some essential oils
  •  Hot process soap making: Add all the ingredients to the pot, place it on a heat source and stir continuously until the soap goes through various stages. The excess water is evaporated and soap is ready to use once it is cooled


What precautions should be taken during this process?

  • Tighten the bottle of lye as moisture will weaken its strength and cause it to form lumps
  • Lye can be fatal if swallowed
  • Always wear rubber gloves, protective clothing and shielding eyewear when working with lye
  • Lye mixed with water releases toxic fumes that irritate the lungs. So work in a well ventilated area
  • Do not use any containers made of zinc, aluminum, and tin as lye reacts with them. Use glass, plastic, enamel, stainless steel and heat proof stoneware
  • If your skin comes into contact with lye wash it off vinegar


The advantages of this process include low cost and can add ingredients as many as you can by following the saponification chart which specifies the amount of lye used for any mixture of oils or fats. Disadvantages include working with lye and the cure time.


External References
Related Videos: 
See video