Glycerin

Glycerin is a three-carbon chain molecule which has an alcohol group bound to each carbon. It is a sweet and viscous liquid used in bakery foods as a humectant, water activity reducer and crystallization modifier. In food chemistry, glycerin is the backbone of fats and mono-, di- and triglycerides.
Glycerin can form links with acid moieties (i.e. fatty acid chains) at the hydroxyl groups, losing a hydrogen and esterifying with these fatty acids to form fats.
• If each of the three arms of glycerin is attached to a fatty acid, the resultant product is a triglyceride.
• If only two are linked, it is a diglyceride.
• If only one is so linked, it is a monoglyceride.
Function
Glycerin is a multifaceted ingredient. The main functions of this molecule include:
• Carrier/solvent for flavor extracts and color mixes
• Sweetener
• Modifier of water activity (aw) in foods
• Shelf-life extender
• Humectant (used to maintain a certain moisture content to prevent the drying-out of foods)
• Crystallization modifier
• Plasticizer
Glycerin is used in confections to maintain the initial level of crystallization of the soft sugar. It also helps prevent ice crystal formation in frozen batter and dough.
Application
High-speed cake making has historically relied on the addition of glycerin and other polyols (e.g. propylene glycol) to obtain aw values as low as 0,85 to 0.80. In such applications, glycerin helps extend the microbial stability and keep a tender and moist mouthfeel in, batter cakes, cake and many other sweet baked goods. Glycerin is also used in non-aerated icings.
Glycerin is usually added to batter cake formulations at levels ranging from 2.0 up to 15.0 % (based on flour weight). The higher the glycerin dose, the more tender the product and more prone to post-baking collapse due to insufficient starch gelatinization and crumb setting. Alternatives to glycerin include sorbitol, propylene glycol and other polyols.
Relevant properties of glycerin
• Solubility: miscible in water and alcohol at 20°C (68°F)
• Molecular weight: 92,1 Da
• Boiling point at standard pressure (101,3 KPa / 0 feet above sea level): 290°C (554°F)
• Melting point: 18°C (64°F)
• Density in aqueous solution at 20°C (68°F): 1230 Kg/m3 (max. water content 5% w/w)
• Relative sweetness: approximately 65% (compared to sucrose)