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I know that glycerin is listed as an allowed synthetic for food processing, but I have also seen it in products used as crop inputs for organic agriculture—does glycerin have a nonsynthetic form?

By Sam Schaefer-Joel

Glycerin, also known as glycerol, is a small molecule with a large variety of uses. Its viscosity, polarity, solubility, and hygroscopic (water absorbing) properties give it a wide range of applications in agriculture, food processing, medicine, microbiology and industrial manufacturing.

Glycerin does not naturally occur in a free form; rather, it is chemically bound to three fatty acids as the backbone of a triglyceride molecule. Triglycerides are the primary constituents of plant and animal oils.

Glycerin is commonly created as a by-product of soap and biodiesel manufacture. During these processes, the bond between the fatty acids and the glycerin backbone is broken, usually by the addition of a strong alkaline base such as sodium or potassium hydroxide. When glycerin is produced through such a reaction, it is considered to be synthetic and is not allowed for use as a crop input in organic agriculture (with the exception of use as an inert ingredient in a formulated pesticide). However, there are several alternative methods to produce glycerin that have been determined to be nonsynthetic by OMRI.

Nonsynthetic glycerin may be produced through fermentation of sugars by yeast. This process was developed by the German biochemist Carl Neuberg during World War I when a British naval blockade prevented the importation of vegetable oils. Glycerin (made from these oils) is essential for the production of nitroglycerin which is used to make a variety of explosives and propellants. Neuberg discovered a technique to block the yeast’s metabolic process that ferments sugars into ethanol, forcing them to produce glycerin by an alternative metabolic process. This method of production is probably the least common in modern times, as growing biodiesel production has increased the amount of cheap glycerin by-product in the marketplace.

Glycerin may also be produced by steam hydrolysis. During steam hydrolysis, water and oils are mixed under high temperature and pressure in an industrial pressure cooker. These conditions allow the water molecules to break the bonds between the fatty acids and the glycerin backbone. Because this process uses physical methods instead of the addition of synthetic chemicals, OMRI has determined this process to be nonsynthetic. Additionally, there is precedent for allowing steam hydrolysis in the production of common soil amendments such as feather meal and bone meal.

Although synthetic glycerin is allowed for processed products at §205.605(b), this allowance does not extend to its use in livestock or crop production. Glycerin may only be used in crop inputs if it is produced by a nonsynthetic process such as fermentation or steam hydrolysis as described here. Organic farmers should check with their certifiers before using glycerin as an input. 

Revised and updated in January 2017 by OMRI Technical Director Johanna Mirenda. This article was originally published in the Winter 2013 edition of the OMRI Materials Review newsletter.