Sugar inversion

Sugar inversion is the chemical conversion of saccharose into glucose and fructose. This process is enhanced by acids and high temperatures.

Saccharose is subject to sugar inversion which changes the composition of the beverage. Since many soft drinks are produced using beet or cane sugar as a sweetener, this chemical reaction has to be closely monitored as the beverage composition gradually changes with progressing sugar inversion.

Measuring the degree of sugar inversion plays a very important role for the production and quality control before, during, and after the production process and is relevant for producers and bottlers of soft drinks with sugar.

The disaccharide sucrose is split up into a 1:1 mixture of the monosaccharides fructose and glucose, one molecule of sucrose consuming one molecule of water. As a consequence, the density of the solution increases with progressing degree of inversion, and the volume decreases. Figure 1 shows the process of sugar inversion.

Saccharose solutions rotate the plane of polarized light. The angle at which the plane of polarized light is rotated is specific for each sugar and depends on its concentration. An aqueous solution of saccharose is dextrorotatory. It causes a specific rotation of +66.5°. The specific rotation of glucose is +52.5°, but fructose is strongly levorotatory (-92°). While inverting, the specific rotation gradually undergoes a change in direction of polarized light from +66.5° to -19.7°. The inverted solution is levorotatory and displays a specific rotation of -19.7°.

$ {52.2° - 92° \over 2} = -19.7° $

Generally, soft drinks are produced by mixing concentrate with water at a defined ratio. Sucrose in the concentrate inverts during storage: the concentrate’s density increases, its volume decreases. The weight of glucose and fructose together after full inversion is 360,32 g/mol whereas the weight of saccharose before inversion is 342,30 g/mol.

$ {360.32 g/mol \over 342.30 g/mol} = 1.053 $

Hence, as Figure 2 illustrates, the progress of sugar inversion must be known before and during soft drink production. To do so, two options exist: the traditional method of forced inversion followed by calculation of °Brix fresh and °Brix inverted, or the instrumental method.

°Brix fresh: °Brix value before inversion
°Brix inverted: °Brix value after full inversion

Forced inversion is a wet chemical method and requires the following steps^[1]:

• Degas the sample (if carbonated)
• Add acid
• Place the sample in a preheated water bath (90 °C, 1 hour)
• Allow the sample to cool
• Measure the density of the sample
• Use an appropriate conversion procedure (e.g. a polynomial function) to calculate the °Brix fresh or °Brix inverted from the measured density. 

If the degree of inversion is also required, the density is measured twice: once after degassing before inversion and once after inversion. The total time consumption per sample is 60 to 120 minutes.

The instrumental method combines density and sound velocity measurements since these two properties are affected differently by the ongoing inversion process. These properties are used as an input for an algorithm which will provide information about concentration sugar fresh, concentration sugar inverted, and the degree of inversion. The instrumental method requires the following steps:

• Degas the sample (if carbonated)
• Inject the sample into the measuring cells of the analytical instrument
• Press <Start>

The total time consumption including degassing is 5 to 10 minutes.

1. All steps described can be seen as a general guideline and might be adapted according to company-internal standards.

• Soft Drink and Syrup Analysis: Soft Drink Analyzer M
• Analysis of inverted regular soft drinks with PBA-SI Generation M
• Inline Brix Measurement, Diet Beverage Analysis and CO₂ Measurement: Cobrix 5
• Online Brix Measurement in Soft Drinks: Brix Monitor
• MCP 5300/5500 Sucromat
• www.softdrinksinternational.com
• www.drinktec.com