Coming clean about saponification

Making homemade soap is convenient and will save you money down the line. The following guidelines will explain the process of saponification -- the chemical process by which soap is formed -- so you can get started on making your own sweet-smelling soap.

In order for saponification to take place, the temperature of the caustic soda solution and fat has to be carefully controlled.

The simplest method is to bring both the caustic soda and the fat to a temperature of 35°C to 37°C (95°F to 98.5°F) before mixing them together. Some experts recommend that the fat be at a higher temperature than the caustic soda: about 52°C (125.5°F) for the fat and 34°C (93°F) for the caustic soda when beef tallow is used, 28°C (82°F) and 23°C 73°F) when lard is used, 41°C (106°F) and 28°C (82°F) for half lard, half tallow.

Occasionally, saponification does not take place and the soap mixture separates into a top layer of fat and a bottom layer of lye solution. Generally, the mixture can be reclaimed by heating it to about 60°C (140°F) while gently stirring with the wooden spoon. Then remove from the heat and keep stirring until the mixture thickens into soap.

• To test your soap solution, take some in the spoon and let a few drops fall back onto the surface of the soap; if the surface supports the drops for a moment or two before reabsorbing them, the soap is ready for the molds.
• After pouring, place the molds in a warm place and leave for 24 hours or so for the soap to set.
• If you have used lined containers, the lining can be lifted out and the soap sliced into cakes.

A whitish scale or residue may form on the surface of the soap as it matures. This is excess sodium salts that have reacted with the air and formed sodium carbonate. This whitish substance must be scraped off before the soap is used, otherwise the soap can have a drying effect on the skin. The longer a soap is left to dry, the milder it becomes.

The ageing process effectively lowers the alkalinity, or pH, of the soap. The lower the pH, the less effect it has on the skin's natural acid mantle. Commercial producers often use citric acid or a similar substance to lower the pH quickly. You can achieve the same effect by letting your soap "cure" for two to three months after you've taken it from the mold.

These simple guidelines will get you started on making homemade soap.