Glycerin

What are the various ways that glycerin is produced and which forms are allowed in organic livestock production?

By Tina Jensen Augustine

Glycerin, or glycerol, is a colorless or pale yellow, viscous liquid that can be derived either from animal and vegetable fats and oils, or from petrochemical feedstocks. Glycerin occurs naturally as the backbone molecule to which fatty acids are bonded in triglycerides, or fats. Synthetic forms of glycerin are permitted for use as livestock teat dips at §205.603(a)(14). The listing requires that the glycerin be produced from the hydrolysis of fats and oils. The listing at §205.603 also classifies such glycerin as synthetic. Nonsynthetic glycerin is also allowed in organic livestock production according to §205.105. Agricultural forms of glycerin used in livestock feed must be organic according to §205.237(a).

There are various ways in which glycerin can be obtained from fats and oils. First, glycerin can be made as a by-product of the soap manufacturing process. During this process, water and oils are mixed with sodium or potassium hydroxide. The triglyceride’s ester bonds are broken when the sodium or potassium ions saponify the fatty acids, leaving the glycerol backbone to then be isolated and purified.

Alternatively, fats and oils are mixed with water under high temperature and pressure, allowing water molecules to break the ester bonds between the fatty acids and the glycerin backbone. The glycerin is concentrated in multistage evaporators and then refined. Purification can be achieved through an ion exchange process or a distillation system.

Crude glycerin is also a by-product of biodiesel production from vegetable sources such as palm oil, rapeseed and soybeans. In this process, refined, bleached vegetable oil is reacted with methanol to carry out a transesterfication reaction in the presence of a catalyst (sodium methylate or potassium sulfate). This yields biodiesel and crude glycerin. The biodiesel and crude glycerin are separated by decanting. Hydrochloric or sulfuric acid may be added to the glycerin, along with sodium or potassium hydroxide to produces salts and water. The salts are then removed in a distillation column, as is any remaining methanol. Pure glycerin steam is taken off the top. Alternatively, the glycerin may be purified via ion exchange. Further refining may be done, such as decolorizing using activated carbon. This process has been considered by the OMRI Review Panel to meet the intent of the National Organic Program (NOP) allowance for glycerin from fats and oils.

The above processes have all been considered by the OMRI Review Panel to be synthetic and also to meet the annotation allowing “hydrolysis of fats and oils.” Glycerin that is made using one of these processes is therefore allowed for use as a livestock teat dip in accordance with §205.603(a)(14).

Glycerin may also be obtained from microbial fermentation of a carbohydrate substrate. One such method described fermentation of sugar by yeast in aerobic conditions. Such glycerin production from fermentation is considered nonsynthetic, and therefore permitted in organic livestock production. Glycerin teat dips are not required to carry an organic certificate.

Finally, glycerin can be produced synthetically from propylene through various methods, all of which are considered synthetic and prohibited for any use in organic production.

This article was originally published in the Summer 2017 edition of the OMRI Materials Review newsletter, and was reviewed and updated by Technical Director Doug Currier in January 2020.