Glycerin

Biodiesel and other oil processors separate fats into their main products and a glycerin rich liquid. The liquid exists because glycerin parts from fatty acids during processing. Further treatment removes alcohol, salts and water.^2,8

1. 01 // Source Oils or fats Vegetable oils or animal fats enter a plant that makes biodiesel or other fat products.
2. 02 // Process Fats split Processing separates fatty acids from glycerin, leaving a glycerin rich liquid beside the main product.
3. 03 // Process Liquid separated In biodiesel production, the denser glycerin liquid settles below the fuel and is drawn off.
4. 04 // Process Impurities removed Further processing removes residual alcohol, salts and water; the amount removed varies by grade.
5. 05 // Output Liquid glycerin A thick liquid reaches the food plant, where it is measured into a recipe.

1. 01

   Keeps chews soft

   Glycerin holds moisture while reducing the water available for microbial growth. Makers use it to keep soft treats pliable alongside other spoilage controls.^3,9

2. 02

   Adds sweet appeal

   It tastes sweet. In a short bowl choice test, dogs favored the glycerin recipes, though preference also depends on the rest of the food.^2,3

3. 03

   Supplies recipe energy

   Dogs use glycerin for energy. As an oil processing byproduct, it can replace some corn when its price and purity suit the recipe.^1,2,8

4. 04

   Lowers extrusion power

   In one dog food trial, the extruder used less power as glycerin replaced some corn. That reduced a processing cost without changing measured kibble quality.²

How much Short dog studies tested diets with 0 to 9% glycerin; another tested semipurified glycerin at up to 10%.^1,2

1. Brands say

   Glycerin gives dogs usable energy

   Evidence

   1. Strong
   2. Some
   3. Thin
   4. None

   An 8 dog crossover and a separate 20 dog feeding test found that dogs used glycerin for energy. Both tested particular batches over short periods; energy value does not equal a wider health benefit.^1,2

2. Brands say

   Glycerin makes any dog food tastier

   Outruns the evidence

   Evidence

   1. Strong
   2. Some
   3. Thin
   4. None

   In a 27 dog bowl test, dogs preferred the recipe with 9% glycerin in about 84% of observations against its control. One set of recipes cannot predict preference for every food.²

3. Brands say

   Glycerin alone keeps soft treats safe

   Outruns the evidence

   Evidence

   1. Strong
   2. Some
   3. Thin
   4. None

   FDA lists glycerin as a humectant, and an industry account describes its use to control water activity in chewy treats. Neither is a dog safety trial. Processing and spoilage controls still matter.^3,9

4. Owners say

   Glycerin in jerky causes kidney failure

   Outruns the evidence

   Evidence

   1. Strong
   2. Some
   3. Thin
   4. None

   FDA reviewed about 5,200 jerky illness complaints and considered glycerin in its investigation, but found no single cause. Those reports do not show that glycerin caused the kidney cases.^4,5