Glycerin is a sugar alcohol that is used in soaps and moisturizing lotions because of its high hygroscopic properties, meaning that it readily absorbs water from the air. Glycerin can also be used for conserving preserved fruit and scientific specimens in biology laboratory work. Glycerin also is useful for the lubrication of molds, for making cakes and candies, making printing ink, and for preventing hydraulic jacks from freezing. While glycerin can be made from vegetable oil, the most common method of making glycerin is to render animal fat. See Step 1 below to learn to make glycerin of your own.
Prepare animal fat for rendering. Any animal fat can be used, but beef fat is most commonly used. Remove all skin, muscle, ligaments, tendons and meat to leave only animal fat, commonly referred to as tallow.
Render the tallow. Cut the tallow into small pieces and melt the tallow over a low flame on the stove in a pot. Stir as needed.
Prepare the lye solution. Pour the lye into the water slowly. The addition of lye to the water will generate heat, so handle the containers carefully. Stir the solution gently.
Cool the tallow. When the tallow has been rendered, remove the tallow from heat and stir.
Ensure that the ingredients are ready to be mixed. The tallow and the lye solution should both be about 95 degrees F (35 degrees C) for proper mixing.
Perform the mixing. Pour the lye solution slowly into the tallow and stir vigorously.
Add the salt. Pour salt into the completed mixture and continue stirring. Add salt until the thick syrup formed floats to the surface with a pool of fluid formed beneath it. Stop stirring.
Remove the syrup. When the mixture has cooled to a consistency that can be scooped out of the pot with a large straining spoon, do so. What remains in the pot will be a liquid with some impurities and salt mixed in. The liquid is glycerin. Decide how to use the syrup. The syrup is actually hard soap. The syrup can be remelted and poured into molds to make bars of soap. Alternatively, the syrup may be discarded in any manner as it is not hazardous.
Strain the glycerin. After the glycerin has cooled, pour the glycerin through a fine strainer to filter out most of the impurities. This will not remove all of the dissolved salt. The glycerin must be distilled to remove the diluted salt. The result is a finished quantity of glycerin.