Quality Control Measures in Sugar
When it comes to sugar production and sugar trading, there are a number of variables that affect the overall quality and ‘grade’ of the sugar. In general, sugar quality can be separated into two distinct varieties, raw and refined.
Refined Sugar vs Raw Sugar
Each has a distinct set of purposes and associated quality control measures, which we will look at in this blog.
What is Raw Sugar?
Raw sugar is any type of sugar that has been through one cycle of crystallisation, and is defined as partially purified sucrose. Therefore, there tends to be more molasses and impurities in raw sugar, as it is yet to be refined. Raw sugar tends to be delivered to suppliers and factories as opposed to straight to a consumer as it is not suitable for direct human consumption. Molasses is a dark, thick syrup that is created during the early stages of sugar production, and the less refined the sugar the more molasses is present. The raw, brown sugar will need to be refined at another factory before it becomes the white sugar that most people are more familiar with.
Properties of Raw Sugar:
- Partly purified Sucrose
- Polarisation of 96 pol on average
- Can be characterised by the sucrose crystals covered with a film of cane molasses
- Crystallised from partly purified cane juice without any further purification.
- Usually produced in a raw sugar mill
How is Sugar Refined?
Refined sugar is a more common product for the average consumer, and can be defined by its purer properties compared to its raw counterpart. The raw sugar is melted to remove these impurities and is essentially purified twice, resulting in a product fit for human consumption. Its white, crystalline appearance is what most consumers would think of when they think of sugar in its table-top form.
Properties of Refined Sugar:
- free from impurities’
- Fit for immediate human consumption with higher polarisation levels
Sugar Quality & How to Test It
The quality of sugar can be categorised using the following four categories:
How to Check Quality of Sugar
Before we go through each category below, it is worth noting that every client will require a different quality of sugar, so it is always measured on a case by case basis. The following quality control measures consider the purity, colour and texture of the sugar.
Sugar Quality: Polarisation
Polarisation (pol) essentially measures the purity of the sugar, with the apparent sucrose content in the product provided as a mass percentage. The higher the polarisation, the purer the sugar is; the lesser the polarisation, the more impurities are present in the sugar.
The method is simple once it is boiled down (if you’ll pardon the pun.) It is measured by the optical rotation of polarised light, (presented in the degree of Z) passing through the sugar. In layman’s terms, this means measuring the amount of light refracted through the final product. If this is a little tricky to get your head around check out these handy resources that go into a little more depth about the polarisation process.
Sugar Quality: ICUMSA Colour Measurement
Another way that sugar quality is measured is through ‘colour’. The term colour refers to a wide range of complex and molecular components that contribute to the overall appearance of sugar.
The processing of cane or beet can produce different scopes in terms of colour. In fact, this was seen as so important that in 1897, ICUMSA was officially formed, also known as The International Commission for Uniform Methods of Sugar Analysis (phew!).
This International Standards body has provided a benchmark in terms of measuring and defining the grade and quality of the sugar, based on the measurement of the yellowness of the sugar. The colour is dependant on the residual molasses that are not removed in the refining process.
You can find out more about the ICUMSA colour scale here.
Sugar Quality: Ash
This term can throw people off but essentially, ash refers to all the inorganic components that are naturally present in the cane or beet. This non-sucrose residue found within the crystal is determined by the conductivity of the solution. The higher the ash in raw sugar, higher refining costs will be incurred as it will take longer to purify and there will be less yield. There is also a reduced yield with sugar that is high in ash, so the lower the ash, the better, really.
Sugar Quality: Moisture
Reducing moisture in sugar is very important, as sugar is hygroscopic (meaning it absorbes moisture from the air) and can cake if it becomes too moist. Generally speaking, moisture in sugar can be separated into three separate categories and is expressed as a percentage:
- Bound moisture – the moisture trapped between the crystallised sugar and a thin surface layer of amorphous sugar
- Internal moisture – the moisture inside the crystal itself
- Free moisture – the surface moisture in the syrup film
The optimal moisture content of refined sugar is typically between 0.02 and 0.05%, and of raw sugar between 0.25 and 1.10%.
Author: Josie Palmer