Glycerin

Glycerin (also called glycerine) is normally sourced as the byproduct of other chemical processes such as biodesiel production and soap making which involve processing triglycerides from animal or plant sources. It can also be can be synthetically produced from petroleum sources.

The International Cosmetic Ingredient Dictionary considers glycerin to be a synthetic ingredient regardless of the source. This may be because it goes through multiple processed for extraction and refining. However, in some cases it might meed the definition of “natural derived” (from ISO 16128 – Natural and Organic Cosmetic Ingredients and Products).

It is a clear, sweet, odorless, viscous liquid. Technically, it’s a sugar alcohol. Glycerin is safe for human consumption and is an allowed food additive in most countries including the United States, Canada, Japan, and European Union. (I use a mix of water, glycerin, and stevia to sweeten my tea.)

Uses

Nearly 100 years ago the primary uses of glycerin were to process smoking tobacco, to make nitroglycerine for explosives, and in anti-freeze for automobiles. It was also used in smaller amounts in candy, gum, soft drinks, baked goods, cosmetics, drugs, bookbinding, and in the manufacture of textiles, paint, paper, floor coverings, printing rollers, and embalming fluid.

At one time, the monthly consumption of glycerin was used as a measurement of the condition of general business!

Currently, glycerin is used in foods, as a humectant, a solvent, and a sweetener. It can be used as a sugar substitute (slightly more calories and slightly less sweet than sugar). Among other things, glycerin is used to keep frosting from getting too hard, as a thickener in liqueurs, and as a sweetener in baked goods.

In prescription and over-the-counter drugs, glycerin is used for a wide variety of purposes. It is found in some prescription wound and burn treatment materials. It is used in laboratories and in medical research. In cosmetics it is generally used to increase smoothness or lubrication, and as a humectant.

Other modern uses of glycerin include electronic cigarette (vape) liquids, botanical tinctures, filming underwater scenes, creating “smoke” effects in films, and much more.

And, of course, in cosmetics glycerin is used as a humectant, moisturizer and to improve the “feel” of cosmetic products.

It is a very versatile substance!

Glycerin From Soap

As noted, glycerin is a by-product of the saponification process. In commercial soap-making processes, the freed glycerin is purified and then sold separately. The commercial soap this way produced has a negligible percentage of glycerin in the final product. As a result, the soap bars tend to be harder.

The facilities and processes necessary to separate and purify glycerin are not available to soap handcrafters. That being the case, in small batch handcrafted soap the glycerin remains in the finished product. Bar soap with the glyercin still in it tends to be somewhat softer than soap where the glycerin has been removed. On the other hand, soap containing glycerin tends to be more moisturizing (less drying) because of the humectant properties of the glycerin.

Handcrafted Soap—How Much Glycerin?

You can actually fairly accurately calculate how much glycerine is in cold or hot process soap. This can be handy if you have decided to list your soap ingredients based on what comes OUT of the pot.

The amount of glycerin in soap is directly proportional to the amount of sodium hydroxide (NaOH) or potassium hydroxide (KOH) that is used.

Amount of Glycerin

The formula for calculating the amount of glycerin is different for NaOH and KOH.

For NaOH soap:

Glycerin weight = 0.77 × (NaOH weight)

For KOH soap:

Glycerin weight = 0.55 × (KOH weight)

Percentage of Glycerin in a Batch

To calculate the percentage of glycerin in the batch (and therefore in the bars in the batch) first you need to know the total total weight to the batch.

Total batch weight = fat/oil + NaOH + KOH + water + additives

Then calculate the percent of glycerin:

Glycerin % = Glycerin weight ÷ total batch weight.


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Discussion

3 responses to “Glycerin”

  1. Some interesting facts about glycerin, thanks Marie! I like the one about glycerin being a measure for the business economy.

    Side note: If I had a dollar for every time someone called The Nova Studio (when we were still in the SF Bay Area) to ask if they can make soap from all the excess glycerin/glycerol produced from biodiesel production. I had to explain that glycerin is a bi-product of soapmaking too, and not something that you USE to make soap. I think the term “glycerin soap” is confusing – people think it’s made FROM glycerin, as opposed to contains more glycerin. (I learned in my research that glycerol from biodiesel is considered “low grade” and not something you’d want to add to your skincare products anyway.)

    Also good for the Vegans & Vegetarians out there to know that glycerin can be from an animal OR a vegetable source, based on what type of fat is used. I wonder of the synthetic versions… are they typically vegetable-based vs animal-based?

    1. I found an interesting article on glycerin production from UnivarSolutions. Apparently nearly all glycerin on the market is byproduct of some other chemical process (soapmaking, production of fatty acids or alcohols, or biodesiel). All of it is highly refined before being sold as one of the various grades of glycerin. UnivarSolutions offers a number of different grades, including tallow based, tech grade, kosher, and also “synthetic glycerin.”

      Even when glycerin is sourced from plants/animals, I think it is still considered “synthetic” because it is considerably removed from the original form and must be chemically processed to be separated and cleaned. That’s slightly different than truly synthetic glycerin, which is actually petroleum-based.

      I expect that a reputable supplier should be able to tell you where the glycerin was sourced – or at least the type and rating of the glycerin.

  2. How interesting. I didn’t realize most glycerin out there was synthetic. I try really hard to keep away from anything synthetic, so I’ll have to watch for this. Thanks for the tip on how to figure glycerin content in my soap too!

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