Many people forget or don’t realise that there are several types of sugar: Glucose or dextrose is by far the most important because it is what our body uses to produce energy but also lactose, sucrose, fructose, inverted sugar, etc. are all examples of sugars that are present in different types of food i.e. milk, fruit, granulated sugar, honey. Inverted Sugar is quite an interesting one and often found in many recipes here at Giapo ice cream in New Zealand. It is unlike a syrup which is just made from dissolving sugar into water and heating it – we use an inverted syrup. Sugars are made up of carbons, hydrogens and oxygen atoms – the different types of sugars are based on the different configurations of these atoms. Inversion in chemistry is the rearrangement of atoms to create different molecular configurations. An inverted syrup can be made by boiling equal parts of water and granulated sugar with a pinch of cream of tartar (acid catalyst) or lemon juice which results in an inverted syrup made up of equal parts of glucose and fructose.
Another example of this is when yeast cells are mixed in a dough (or beer), they begin their digestion process by releasing an activated enzyme called invertase. This breaks down sucrose into simpler components – glucose and fructose. This reaction is called hydrolysis (breaking of bonds and addition of water) and is used to split up a complex molecule into its simple constituents.
Invert syrups are favourable in food processes in these ways:
- hygroscopic properties: absorbs moisture from the atmosphere so longer shelf life.
- sweeter than sucrose syrups: use less for the same amount of sweetness because 50% is fructose.
- easier to dissolve: preferable in cooking.
As mentioned before, there are two ways in which you can make an invert syrup – addition of an enzyme or addition of an acid. If preparing using an enzyme, heating plays an important part – it is required to dissolve the sucrose into the water and facilitate the process, however, if it is above 70 degrees Celsius it can denature the enzymes and also dissolve the water. If this happens you are less likely to get an equal amount of the final products: glucose and fructose. Loss of water in the invert syrup can also lead to crystallisation which defeats the purpose of creating a syrup in the first place.
Addition of acid (or acid hydrolysis) is the alternative and more accessible in the everyday kitchen. Using cream of tartar or lemon juice is adding a catalyst (this is an ingredient which speeds up the reaction but does not become part of the finished product) as it speeds up the conversion process. Acidic environments in general speed up the conversion as yeast cells also produce acid in the fermentation process, resulting in lowering of the pH levels or increasing acidity for a faster chemical reaction.
In the conversion of sugar and water to an invert syrup, the sucrose molecule divides into the glucose segments which acquire the oxygen (O) that connected the two halves and the H+ (hydron) ion of the water (H2O) molecule; the fructose segment gets the OH- (hydroxide) ion. The reaction looks like this: C12H22O11 (sucrose) + H2O (water) in the presence of an acid = C6H12O6 (glucose) + C6H12O6 (fructose) or invert syrup.
If you were to count the amount of carbon (C), oxygen (O), and hydrogen (H) atoms on equation, you will see that they are exactly the same amount from the start of the reaction to the end. All the atoms present in the sucrose molecule are now the new glucose and fructose molecules. The ‘absorption’ of the water molecule is why the invert syrup remains in syrup form, instead of settling out or crystallising as a simple sugar/water mixture because there is not water to evaporate off. As a result, the total solids in the newly created invert syrup are about 5% higher than the total solids of the sugar/water mixture you started with! The reaction increases the number of H+ and OH- sites from 13 on the sucrose molecule to 18 on the glucose and fructose molecules. These sites attract the H+ and OH- ions of water present in the atmosphere and since there are more sites in the invert syrup than in the original sucrose there is an increase in hygroscopic properties. The respective positive H+ions and negative OH- ions in water are attracted to the negative OH- and positive H+ sites on the sugar molecules.
In addition to increased moisture retention ability, converting sucrose to invert syrup has two other interesting results: increased sweetness and better solubility. On a sweetness scale where sucrose is set at 100, invert syrup ranks about 130. Therefore using an invert syrup in formulas can allow you to cut back on the total amount of sugar used and still maintain the same sweetness in the finished product!