Castile soap is named for the Castile region in Spain. Pure Castile soap is a rarity these days because of its time-consuming manufacturing process. Castile soap uses 100 per cent olive oil as its base, whereas most soap manufacturers add other oils such as coconut or palm to quicken the curing process. Although many soaps use the "Castile" term to imply purity, gentleness, quality and the absence of animal fats, few are actually 100 per cent pure. One of the most ancient and simplest methods for creating pure Castile soap is using the cold process method.
Prepare your workstation by setting out all ingredients to ensure easy access and organisation. Put on your goggles and gloves. You will be working with caustic chemicals, so safety is important.
Pour the olive oil and the quart of water into a large bowl. Use a bowl made out of a nonreactive material such as ceramic, glass or plastic.
Add the lye to the second bowl, and, using extreme care, slowly add the additional 3/4 cup cold water to the bowl without splashing. A chemical reaction between the water and lye will cause the mixture to bubble and steam.
Add the lye solution to the olive oil and water base carefully and slowly. Add a little at a time, stirring constantly with your long-handled spoon as you combine the mixtures.
Stir the mixture with the wooden spoon, always mixing in the same direction, according to spanishjourneys.com. As you mix, you'll begin to see trails of soap forming. Continue mixing until it thickens to the consistency of thick cream. This might take up to an hour.
Pour the creamy soap mixture into your soap moulds or loaf pans, and set aside for at least 48 hours. Check the soap after 12 hours, and if separation has occurred, stir the liquid on top back into the soap mixture.
Turn out the finished soap after it has fully solidified. This will usually take about three days. Slice the soap into bars, and wrap in parchment paper to dry and cure for another two weeks before using.
You can use used oil for making this soap, especially if the oil was used for frying mild foods on gentle heat. Strain it to clean, and you're ready to begin.
Lye is caustic and can burn your skin and your work area. Always exercise extreme caution when working with chemicals. Protect your work area with old towels or newspapers, and always wear safety goggles and gloves when handling lye.