Why do extracts include alcohol?
Extracts have that name because flavor compounds are extracted with a solvent, which is usually alcohol. Alcohol performs this action faster than glycerin, and it extracts a different variety of substances than glycerin will extract.
What is Glycerin?
Glycerin (pronouncedGLIH–sir–in) is classified as a type of carbohydrate called a sugar alcohol, or polyol. Glycerin is another name forglycerol, the three-carbon backbone of atriglyceride. It is formed naturally through the alcoholic fermentation of sugars; however, most of the glycerin we consume is produced from the hydrolysis of fats and oils, and in lesser quantities through the fermentation of yeast, sugar or starch.
Glycerin is used as an ingredient in a variety of food and beverage products to help retain moisture,prevent sugar crystallization, and add bulk, smoothness, softness, sweetness and texture.
Like most sugar alcohols, glycerin is not as sweet as sugar—it is about 60–75% as sweet. Glycerin is more calorie-dense than other sugar alcohols and contains more calories per gram (4.32) than sugar (3.87).
From another source...
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in those lipids known as glycerides. Due to having antimicrobial and antiviral properties it is widely used in FDA approved wound and burn treatments.