Tuesday, January 22, 2013

Invert Syrup: A Primer

Invert syrups are commonly used to sweeten liqueurs and cordials, though most consumers don't have a good understanding of what they are or how they are made.

Invert syrup is a sugar syrup composed of equal parts glucose (C6H12O6) and fructose (C6H12O6), derived from splitting a solution of sucrose (C12H22O11) in water (H2O) into these component parts.

Name Derivation
The concentration of a sugar syrup can be measured by passing polarized light (light whose waves are all aligned in a single plane which can be measured before and after it enters the syrup) through the solution and measuring the degree of light wave rotation upon exiting.  A solution of pure sucrose will rotate the light 66.5 degrees to the right, and as the sucrose is converted into glucose and fructose the exiting light will begin rotating to the left.  A fully converted sugar will have an exit rotation of 39 degrees to the left.  This inversion of the rotation from right to left gives the converted syrup its name.

Other Names
Inverted syrup, trimoline.

Sucrose is a disaccharide, which indicates that it is composed of two simpler monosaccharides (glucose and fructose).  By heating a solution of sucrose in water, a hydrolysis reaction is induced which splits the disaccharide into its two component parts.  By adding an acid catalyst such as lemon juice (10ml per kg sugar) or cream of tartar (1g per kg sugar), the reaction can be accelerated.  Pastry chefs often make invert syrup by cooking sucrose syrup with an acid until a thicker syrup is formed (e.g., boiling a sucrose/acid solution for 20 minutes at 237°F).  Invert syrup can be made in varying thicknesses based on the ratio of sugar to water, and can be converted to varying degrees (up to about 85% glucose/fructose) based on the reaction time.

Naturally Occurring Forms
Honey, jams.

Light to medium gold.

Noticeably sweeter than sucrose.

-Invert syrup will resist crystallization longer than sucrose syrup.
-If invert syrup begins to solidify, it can be re-liquefied by warming gently.
-Invert syrup creates products that are smoother and less granular than sucrose syrup.
-Invert syrup retains more moisture than sucrose syrup, so it adds preservative qualities to products and has a longer shelf life.
-Invert syrup is an important ingredient in low-fat goods, as it replaces the moisture content that would be provided by fat.
-All constituent sugars (sucrose, glucose, and fructose) support fermentation, so invert syrup can be fermented as easily as sucrose syrup.