Inverted sugar syrup

Inverted sugar syrup, also called invert syrup and invert sugar, is an edible mixture of two simple sugars—glucose and fructose—that is made by heating sucrose (table sugar) with water. It is thought to be sweeter than table sugar, and foods that contain invert retain moisture better and crystallize less easily than do those that use table sugar instead. Bakers, who call it "invert syrup", may use it more than other sweeteners.
Though inverted sugar syrup can be made by heating table sugar in water alone, the reaction can be sped up by adding lemon juice, cream of tartar, or other catalysts, often without changing the flavor noticeably.
The mixture of the two simple sugars is formed by the hydrolysis of sucrose. This mixture's optical rotation is opposite to that of the original sugar, which is why it is called an "invert" sugar.
Chemistry.
Table sugar (sucrose) is converted to invert sugar by hydrolysis. Heating a mixture or solution of table sugar and water breaks the chemical bond that links together the two simple-sugar components.
The balanced chemical equation for the hydrolysis of sucrose into glucose and fructose is:
Optical rotation.
Once a sucrose solution has had some of its sucrose turned into glucose and fructose the solution is no longer said to be pure. The gradual decrease in purity of a sucrose solution as it is hydrolyzed affects a chemical property of the solution called optical rotation that can be used to figure out how much of the sucrose has been hydrolyzed and therefore whether the solution has been inverted or not.
Definition and measurement.
A kind of light called plane polarized light can be shone through a sucrose solution as it is heated up for hydrolysis. Such light has an 'angle' that can be measured using a tool called a polarimeter. When such light is shone through a solution of pure sucrose it comes out the other side with a different angle than when it entered, which is proportional to both the concentration of the sugar and the length of the path of light through the solution; its angle is therefore said to be 'rotated' and how many degrees the angle has changed (the degree of its rotation or its 'optical rotation') is given a letter name, formula_1 (alpha). When the rotation between the angle the light has when it enters and when it exits is in the clockwise direction, the light is said to be 'rotated right' and formula_1 is given to have a "positive" angle such as 64°. When the rotation between the angle the light has when it enters and when it exits is in the counterclockwise direction, the light is said to be 'rotated left' and formula_1 is given a "negative" angle such as −39°.
Definition of the inversion point.
When plane polarized light enters and exits a solution of "pure" sucrose its angle is rotated 66.5° (clockwise or to the right). As the sucrose is heated up and hydrolyzed the amount of glucose and fructose in the mixture increases and the optical rotation decreases. After formula_1 passes zero and becomes a negative optical rotation, meaning that the rotation between the angle the light has when it enters and when it exits is in the counter clockwise direction, it is said that the optical rotation has 'inverted' its direction. This leads to the definition of an 'inversion point' as the per cent amount sucrose that has to be hydrolyzed before formula_1 equals zero. Any solution which has passed the inversion point (and therefore has a negative value of formula_1) is said to be 'inverted'.
Chirality and specific rotation.
As the shapes of the molecules ('chemical structures') of sucrose, glucose, and fructose are all asymmetrical the three sugars come in several different forms, called stereoisomers. The existence of these forms is what gives rise to these chemicals' optical properties. When plane polarized light passes through a pure solution of one of these "forms" of one of the sugars it is thought to hit and 'glance off' certain asymmetrical chemical bonds within the molecule of that form of that sugar. Because those particular bonds (which in cyclic sugars like sucrose, glucose, and fructose include a kind of bond called an anomeric bond) are different in each form of the sugar, each form rotates the light to a different degree.
When any one form of a sugar is purified and put in water, it rapidly takes other forms of the same sugar. This means that a solution of a pure sugar normally has all of its stereoisomers present in the solution in different amounts which usually do not change much. This has an 'averaging' effect on all of the optical rotation angles (formula_1 values) of the different forms of the sugar and leads to the pure sugar solution having its own 'total' optical rotation, which is called its 'specific rotation' or 'observed specific rotation' and which is written as formula_8.
Effects of water.
Water molecules do not have chirality, therefore they do not have any effect on the measurement of optical rotation. When plane polarized light enters a body of pure water its angle is no different than when it exits. Thus, for water, formula_8 = 0°. Chemicals that, like water, have specific rotations that equal zero degrees are called 'optically inactive' chemicals and like water, they do not need to be considered when calculating optical rotation, outside of the concentration and path length.
Mixtures in general.
The overall optical rotation of a mixture of chemicals can be calculated if the proportion of the amount of each chemical in the solution is known. If there are formula_10-many optically active different chemicals ('chemical species') in a solution and the molar concentration (the number of moles of each chemical per liter of liquid solution) of each chemical in the solution is known and written as formula_11 (where formula_12 is a number used to identify the chemical species); and if each species has a specific rotation (the optical rotation of that chemical were it made as a pure solution) written as formula_13, then the mixture has the overall optical rotationformula_14Where formula_15 is the mole fraction of the formula_16 species.
Fully hydrolyzed sucrose.
Assuming no extra chemical products are formed by accident (that is, there are no side reactions) a completely hydrolyzed sucrose solution no longer has any sucrose and is a half-and-half mixture of glucose and fructose. This solution has the optical rotation
formula_17
Partly hydrolyzed sucrose.
If a sucrose solution has been partly hydrolyzed, then it contains sucrose, glucose and fructose and its optical rotation angle depends on the relative amounts of each for the solution;formula_18Where formula_19, formula_20, and formula_21 stand for sucrose, glucose, and fructose.
The particular values of formula_22 do not need to be known to make use of this equation as the inversion point (per cent amount of sucrose that must be hydrolyzed before the solution is inverted) can be calculated from the specific rotation angles of the pure sugars. The reaction stoichiometry (the fact that hydrolyzing one sucrose molecule makes one glucose molecule and one fructose molecule) shows that when a solution begins with formula_23 moles of sucrose and no glucose nor fructose and formula_24 moles of sucrose are then hydrolyzed the resulting solution has formula_25 moles of sucrose, formula_24 moles of glucose and formula_24 moles of fructose. The total number of moles of sugars in the solution is therefore formula_28and the reaction progress (per cent completion of the hydrolysis reaction) equals formula_29. It can be shown that the solution's optical rotation angle is a function of (explicitly depends on) this per cent reaction progress. When the quantity formula_30 is written as formula_31 and the reaction is formula_32 done, the optical rotation angle is
formula_33
By definition, formula_1 equals zero degrees at the 'inversion point'; to find the inversion point, therefore, alpha is set equal to zero and the equation is manipulated to find formula_31. This givesformula_36Thus it is found that a sucrose solution is inverted once at least formula_37 of the sucrose has been hydrolyzed into glucose and fructose.
Monitoring reaction progress.
Holding a sucrose solution at temperatures of hydrolyzes no more than about 85% of its sucrose. Finding formula_1 when r = 0.85 shows that the optical rotation of the solution after hydrolysis is done is −12.7° this reaction is said to invert the sugar because its final optical rotation is less than zero. A polarimeter can be used to figure out when the inversion is done by detecting whether the optical rotation of the solution at an earlier time in its hydrolysis reaction equals −12.7°.
Production.
Common sugar can be inverted quickly by mixing sugar and citric acid or cream of tartar at a ratio of about 1000:1 by weight and adding water. If lemon juice which is about five percent citric acid by weight is used instead then the ratio becomes 50:1. Such a mixture, heated to and added to another food, prevents crystallization without tasting sour.
Inverted sugar syrup can be made without acids or enzymes by heating it up alone: two parts granulated sugar and one part water, simmered for five to seven minutes, will be partly inverted.
Commercially prepared enzyme-catalyzed solutions are inverted at . 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 catalyzed solutions may be inverted at the relatively low temperature of . The optimum pH for acid-catalyzed 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.
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 of any composition can be fermented.
Shelf life.
Fully inverted sugar's low water content improves the shelf lives of products that contain it. The shelf life of partly inverted sugar is about six months and varies by storage and climatic conditions.
Crystallized invert sugar solutions can be restored to their liquid state by gently heating.