Inverted sugar syrup

Chemical reaction of the inversion

The term "inverted" is derived from the practice of measuring the concentration of sugar syrup using a polarimeter. Plane polarized light, when passed through a sample of pure sucrose solution, is rotated to the right (optical rotation). As the solution is converted to a mixture of sucrose, fructose and glucose, the amount of rotation is reduced until (in a fully converted solution) the direction of rotation has changed (inverted) from right to left.

C₁₂H₂₂O₁₁ (sucrose, Specific rotation = +66.5°) + H₂O (water, no rotation) → C₆H₁₂O₆ (glucose, Specific rotation = +52.7°) + C₆H₁₂O₆ (fructose, Specific rotation = −92°) net: +66.5° converts to −19.65° (half of the sum of the specific rotation of fructose and glucose)

Hydrolysis is a chemical reaction in which a molecule breaks down by the addition of water. Hydrolysis of sucrose yields glucose and fructose about 85%; the reaction temperature can be maintained at 50–60 °C (122–140 °F).

Inverting sugar

Inverted sugar syrup can be easily made by adding water and roughly one gram of citric acid per kilogram of sugar. (Lemon juice is 5% to 6% citric acid, with a negligible amount of ascorbic acid, so this would correspond to about 20 grams of lemon juice per kilogram of sugar.) Cream of tartar (one gram per kilogram) or fresh lemon juice (10 milliliters per kilogram) may also be used.

The mixture is boiled to get to a temperature of 114 °C (237 °F), and will convert enough of the sucrose to effectively prevent crystallization, without giving a noticeably sour taste. Invert sugar syrup may also be produced without the use of acids or enzymes by thermal means alone: two parts granulated sucrose and one part water simmered for five to seven minutes will convert a modest portion to invert sugar.

Commercially prepared enzyme-catalyzed solutions are inverted at 60 °C (140 °F). The optimum pH for inversion is 5.0. Invertase is added at a rate of about 0.15% of the syrup's weight, and inversion time will be about 8 hours. When completed the syrup temperature is raised to inactivate the invertase, but the syrup is concentrated in a vacuum evaporator to preserve color.

Commercially prepared hydrochloric-acid catalysed solutions may be inverted at the relatively low temperature of 50 °C (122 °F). The optimum pH for acid-catalysed inversion is 2.15. As the inversion temperature is increased, the inversion time decreases. They are neutralized when the desired level of inversion is reached.

In confectionery and candy making, cream of tartar is commonly used as the acidulant, with typical amounts in the range of 0.15-0.25% of the sugar's weight. The use of cream of tartar imparts a honey-like flavor to the syrup. After the inversion is completed, it may be neutralized with baking soda using a weight of 45% of the cream of tartar's weight.

When adding baking soda and whipping or mixing, the hot syrup will foam and bubble up, so some care is required. A much taller pan than otherwise needed will contain the foam. Make sure there is enough water remaining in the syrup to dissolve the baking soda. Alternatively, dissolve the baking soda in a little extra water, and ensure the syrup's temperature is somewhat below 100 °C (212 °F).

The amount of water can be increased to increase the time it takes to reach the desired final temperature, and increasing the time increases the amount of inversion that occurs. In general, higher final temperatures result in thicker syrups, and lower final temperatures, in thinner ones.

All constituent sugars (sucrose, glucose and fructose) support fermentation, so invert sugar solutions may be fermented as readily as sucrose solutions.

Shelf life

Invert sugar provides more powerful preserving qualities (a longer shelf life) to products that use it.

The shelf life of partial inverts is approximately six months, depending on storage and climatic conditions. Crystallized invert sugar solutions may be restored to their liquid state by gently heating.

Notable uses

Honey is a mixture (principally) of glucose and fructose, giving it similar properties to invert syrup. This gives it the ability to remain liquid for long periods of time.

Jam, when made, produces invert sugar during extensive heating under the action of the acid in the fruit. The large quantities of monosaccharides produced then allows for the product to be stored for relatively long periods of time, with the sugar acting as a preservative.

Golden syrup is a syrup of approximately 56% invert syrup, 44% sucrose.

Fondant filling for chocolates is unique in that the conversion enzyme is added, but not activated by acidification (microenvironment pH adjustment) or cofactor addition depending on the enzyme(s), before the filling is enrobed with chocolate. The very viscous (and thus formable) filling then becomes less viscous with time, giving the creamy consistency desired. This results from the sub-optimal enzyme(s) conditions purposely created by withholding activation factors, which allows only a fraction of the enzyme(s) to be active, or allows all enzyme(s) to proceed at only a fraction of the biological rate [biologically, it's realistically a combination of both: a reduced number of functional enzymes, with the ones that do function having reduced catalytic kinetics/rates].

Cigarettes use inverted sugar as a casing to add flavour.

Alcoholic beverage manufacturers often add invert sugar in the production of drinks like gin, beer and sparkling wines for flavouring. Candi sugar is a type of invert sugar used in the brewing of Belgian-style beers to boost alcohol content without drastically increasing the body of the beer; it is frequently found in the styles of beer known as dubbel and tripel.

Cadbury Creme Eggs are filled with inverted sugar syrup produced by processing fondant with invertase.