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How sugar quality is tested

Sugar has been part of the human diet for as long as we’ve wandered the earth. Every culture, both modern and ancient has foods that contain natural sugars and in more recent years, added sugars are enjoyed and consumed across a wide variety of dishes. Australia is in the top ten producers of sugarcane in the world and the quality of the sugar we grow, mill and refine is some of the highest in the world. We adhere to the CODEX and the ANZ Food Standards Code to produce high quality and safe food, but what is the process to test the sugar we produce for quality?  

What are the technical parameters for establishing sugar quality?

Like any other product, sugar has a range of quality assurance and technical processes it must undertake during the refining process to ensure consistency of quality. The CODEX Alimentarius standard for sugars and the Australian and New Zealand Food Standards Code provide the food regulations, to which all sugar producers must legally adhere. 

Certain industries and manufacturers that use sugar also have different quality indicators they want or need for the specific product they are making. For example, a food or beverage manufacturer may use manufacturer’s sugar, a product that has a broad crystal size spectrum and contains both fine sugar and larger crystals. The variation in size may not affect the final product's overall quality whereas a baker or confectionery producer using extra coarse sugar as a decorative agent may require a higher consistency of crystal size. 

Let’s explore some of the more technical quality indicators used for the different types of sugars that are available. Some of these quality indicators will be set during the milling process, whilst others will be tested in the final product. 

Polarisation also known as (pol)

Pol is the measurable percentage of sucrose in raw sugar and are a major component in setting benchmarks for exportability of raw sugar. Pol level is managed at the mill during the refining process and is primarily influenced by the quantity of molasses that remains on the surface of the raw sugar crystals during the centrifugal process called Affination.

Note: if you would like to know more about the sugar refining process and Affination, read our article Refining sugar cane.

Refining sugar to reach a certain pol can be a complex process with many variables influencing the overall quality of the sugar that’s produced. Pol is measured by preparing a standard sugar solution and measuring the optical rotation of polarised light passing through. This can be impacted by ash, dextran and starch, which are impurities from the refining process. Also, by dextran and other particles present in small amounts that can modify the crystal shape. Sugar of 98 degrees pol contains about 98% sucrose. 

Colour

Colour of the sugar is vitally important for food manufacturers as it can affects the look of their overall end product that uses sugar. Several processes result in different colours of both raw sugars and refined sugars. 

Cane that is harvested green for example, will typically have a lower colour than cane sugar that is burnt before harvesting. Heat produced by flames close to the outside of the stalk impacts on juice contained within the plant, changing the colour during the milling and refining process.

Mill equipment, nitrogen rich fertilisers and levels of polymers, flavonoids and phenolic acids all change the colour of sugars produced for export or the table. Millers will use a range of quality testing methods to minimise colour formation including the process of decolourisation where liquid sugar is passed over bone char, granular carbon or ion exchange resin which absorbs any remaining colour. 

Moisture

The moisture levels in sugar will influence how raw sugars can be handled. Sugar with a high moisture content is difficult to handle and may impact the machinery and equipment used to transport sugar or used in the food manufacturing process. Sugar that is too wet can start to deteriorate to the point where it is unsuitable for use by food manufacturers. 

At the other end of the spectrum, sugar that is too dry can create a dust hazard when being handled or transported. As sugar dust is flammable under certain temperature and humidity conditions along with the introduction of an ignition source, levels of moisture is one of the most important quality factors when establishing safe work practices for the transportation, handling and storage of sugar. Management of these risks is very high priority for the sugar industry, both for quality and for health and safety reasons.

Ash

When people think of ash (as it relates to sugar), often they think of cane fields burning and the ash from this process making it into the refining process, however, in the case of quality analysis, ash is the measure of the total amount or minerals (or inorganic residue) present in sugar once water and organic matter has been removed. 

Minerals that are tested for that impact the quality of sugar include chlorides, phosphates, sulphates, potassium, aluminium, magnesium along with traces of clay and sand. Too much ash will increase the solubility of sucrose in water which in turn reduces the quantity of pure sugar that can be produced at the mill or in a refinery.

Filterability

Filterability is a measurable rate at which a raw sugar solution can flow through a filter that often replicates a carbonation-based refinery environment. This type of quality test helps to determine the throughput rate at which sugar can flow through a refinery. 

Filterability testing can help determine if insoluble impurities are present in the sugar solution which impacts on thermal efficiency throughout the clarification process and can lead to increased costs for refineries. 

Fine Grain 

Fine grain refers to the size of sugar crystals when compared to optimal screening sizes. A large variation in sugar crystal size can lead to poor separation during the affination process which causes an excess of impurities to be retained by the molasses layer on the outside of the sugar crystal. This inevitably leads to an increase in production cost for refineries as they will need to deal with these impurities. 

Note: if you would like to know more about Affination, read our article Refining sugar cane.

Dextran

Dextran is a naturally occurring polysaccharide that is produced by bacteria that can infect sugar cane stalks when cut or damaged. Higher levels of dextran can increase sugar solution viscosity which in turn affects centrifugal separation and the shape of crystals during refining. To alleviate this refineries need to conduct longer fugal cycles and increase wash water usage which negatively affects throughput and overall sugar yield. 

As you can see there are several different areas of tight quality control and rigorous testing when inspecting the quality of sugar. Australian sugar producers have some of the most thorough testing methods in the world implemented at all three levels of sugar production (growing, milling and refining). These stringent testing requirements ensure we meet the legal and food standards requirements but also ensure Australia consistently produces some of the highest quality sugar in the world. 



References

https://elibrary.sugarresearch.com.au/bitstream/handle/11079/15541/Chapter%2018%20Sugar%20Quality%20and%20What%20Affects%20it.pdf?sequence=38&isAllowed=y

https://www.isosugar.org/sugarsector/sugar

https://www.sugaraustralia.com.au/sugar-australia/products/industrial-products/liquid-sugars/

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