Erythritol is a four-carbon sugar alcohol. It is a monosaccharide, which means it cannot be broken down into other sugars. One molecule of erythritol is formed from 4 carbon atoms, 10 hydrogen atoms and 4 oxygen atoms. It is a sugar alcohol because it is made via a fermenting process and has a specific chemical structure, called a hydroxyl group, attached to one end of the molecule. It is primarily used as a low-calorie sweetener because it is not utilized by the body and is approximately 60 to 80 percent as sweet as sucrose (common table sugar).

Erythritol can be found naturally in many organisms, which indicates that it is a byproduct of metabolism of sugar. According to a review found in the December issue of Food and Chemical Toxicology, erythritol can be found in such fermented beverages as wine, beer and sake, as well as in products made from pears, grapes, watermelon and soy. It can also be found in the tissues and fluids of human and other animals, in human urine and blood (at levels up to one milligram per liter). This is further evidence that erythritol is made as the result of sugar breakdown.

Erythritol is normally made from glucose that is created from corn or wheat starch. To do this, the starch is first treated with enzymes (special proteins) that break the starch down into glucose. This glucose is then mixed with yeast, such as Moniliella pollinis or Trichosporonoides megachliensis, and the yeast ferments the glucose to form erythritol. The fermented mixture is then heated (in order to kill off the yeast) an dried (by boiling off all the water) so that erythritol crystals are formed. These crystals are then washed (to remove impurities), redissolved, purified again (using a special kind of chemical filter) and finally are isolated in solid form, at which point the erythritol is safe for human consumption.