Classic Bells > Soapy stuff > Lactic acid, Sodium lactate, Ascorbic acid

Lactic acid in soap

What does it do in soap? Lactic acid is the acid in yogurt, buttermilk, and other fermented dairy products. Lactic acid is also produced by bacterial fermentation of sugars. Lactic acid and Sodium hydroxide (NaOH) make Sodium lactate.

How much should I use?

Lactic acid is usually added indirectly to soap by using yogurt or buttermilk in the recipe. Yogurt may contain from 0.5% to 1% lactic acid. If using yogurt as a substitute for all water in a "full water" soap, the substitution would add roughly 2 to 4 grams of lactic acid per 1000 grams of oils (0.2% to 0.4% ppo). Generally fermented dairy is used only as part of the water phase, however.

Lactic acid is seldom added to soap in its pure form, but if using pure lactic acid, try 5 to 10 g lactic acid per 1000 g oils (0.5% to 1% ppo).

How much lye does it neutralize? 10 g lactic acid neutralizes 4.44 g NaOH. 10 g lactic acid neutralizes 6.23 g KOH. When using lactic acid in your recipe, add the appropriate extra weight of lye needed to react with the acid. If you do not add extra lye, the acid will increase the superfat in your soap.

How should I add it to my soap? If used as a partial subsitute for some of the water in the recipe, fermented dairy is often blended into the oils before adding the lye solution. If using pure lactic acid, stir it into the water you will use to make your lye solution, add the lye to the water, and proceed with your recipe as usual.

 

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 cold process 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. If you purchase SL powder, I recommend making a 60% solution by mixing 60 grams of the powder with 40 grams of distilled water. SL solution should always be stored in an airtight, opaque container -- exposure to light causes SL solution to degrade.

How much should I use?

Bar (NaOH) soap: Typical dosage is 10 g to 20 g of 60% sodium lactate solution per 1000 g of oils (1% to 2% ppo). Dosage range is 10 to 30 g of SL solution per 1000 g of oils (1% to 3% ppo). Over 3% SL can make bar soap softer and more rubbery, so "more is NOT always better."

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? Method 1: Stir the SL powder or solution into the water you will use to make your lye solution. Add the lye to the water and proceed with your recipe as usual. Method 2: If using a SL solution, blend it into your fats, add the lye solution, and soap as usual.

 

Ascorbic acid (Vitamin C) in soap

What does it do in soap? Ascorbic acid and Sodium hydroxide (NaOH) make Sodium ascorbate in soap. Ascorbic acid and sodium ascorbate are both considered to be Vitamin C, an important dietary additive.

How much should I use? This acid is not often used directly in soap. Try 10 g ascorbic acid for every 1000 g oils (1% ppo).

How much lye does it neutralize? 10 g ascorbic acid neutralizes 2.02 g NaOH. 10 g ascorbic acid neutralizes 2.83 g KOH. When using ascorbic acid in your recipe, add the appropriate extra weight of lye needed to react with the acid. If you do not add extra lye, the acid will increase the superfat in your soap.

How should I add it to my soap? Stir the ascorbic acid into the water you will use to make your lye solution. Add the lye to the water and proceed with your recipe as usual.