Sodium lactate in soap
What does it do in soap? Sodium lactate (SL) is used as a humectant and moisturizer in cosmetic products. In soap, sodium lactate makes hot process soap more pourable and smooth, adds hardness to bar soap, and makes it easier to dilute liquid soap.
What kind to use? Sodium lactate is sold in pure powder form and as a liquid solution containing 60% sodium lactate. The liquid is more convenient to weigh and use for soap and cosmetics, since only small amounts of SL are needed.
The powder is hygroscopic (absorbs water from the air) so it requires careful storage and handling. If you purchase SL powder, I recommend making a 60% solution by mixing 60 grams of the powder with 40 grams of distilled water and add that solution to your products rather than the powder.
SL solution should always be stored in an airtight, opaque container -- exposure to light causes SL solution to degrade.
Sodium lactate is also formed when you add a source of lactic acid to your recipe. Lactic acid is found in fermented dairy products such as yogurt, buttermilk, and kefir.
How much should I use?
Bar (NaOH) soap: Typical dosage is 20 g to 30 g of 60% sodium lactate solution per 1000 g of oils (2% to 3% ppo). Dosage range is 10 to 30 g of SL solution per 1000 g of oils (1% to 3% ppo). Over 3% can make bar soap softer and more rubbery, so more is NOT always better.
Some soapers adjust the amount of SL depending on the fats. They use more SL for a bar soap recipe high in liquid fats and less for a bar soap recipe high in solid fats.
Liquid (KOH) soap: Typical dosage is 30 g of 60% sodium lactate solution per 1000 g of diluted soap weight (3% of diluted soap weight). Diluted soap weight is the sum of the soap paste weight + dilution water weight.
How much lye does it neutralize? None! Do not adjust your lye weight when using sodium lactate.
How should I add it to my soap?
Bar (NaOH) soap: If using SL solution, blend it into your fats, add the lye solution, and soap as usual. If using SL powder, dissolve the sodium lactate in about 2 times its weight of water. Stick blend that mixture into your oils.
Liquid (KOH) soap: Stir the SL powder or solution into the dilution water.