The Sugar Series : Quality Control Measures in Sugar

December 5, 2019

Carys Wright

Teaspoons with brown and white sugar in them

Quality is of utmost importance in all commodity trading, and can impact the price, viability and legitimacy of a product. In the food and beverage industry, ‘quality’ means the combination of all attributes of a particular food item, for example appearance, flavour, nutritional content etc. There is an inherent chemical element to the determination of these attributes, and many food ingredients have particular values that must be met in order for them to meet the specifications of manufacturers. Each ingredient has its own language, with terms denoting different elements of the food product that must be taken into consideration.

The different types of sugar

So we should first ask the question, ‘what is sugar‘ as it takes many forms in its journey from plant to plate? However, when it comes to sugar 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. Each has distinct uses, characteristics and associated quality control measures. Briefly, the main different types of sugar are:

Raw Sugar

What is raw sugar?

Raw sugar is not exactly ‘raw’, as sugar cane and sugar beet must be processed to extract their sugar content. Any sugar that has been through this first cycle of crystallisation, at a sugar mill, is defined as partially purified sucrose – also known as raw sugar.

The word ‘partially’ is important here. Not all of the natural impurities of sugar are removed in the first stage of processing, and there is a higher molasses and impurities content in raw sugar, as it is yet to be refined. Raw sugar is not suitable for direct human consumption, so is most commonly bought in bulk by food processors for use in food production

The amount of molasses is a measure that can be used to gauge quality in raw sugar. 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.

Refined Sugar

What is refined sugar?

Refined sugar is sugar that has been through two stages of crystallisation, first at a mill and then at a refinery. The resulting sugar can be defined by its purity in comparison to its raw counterpart. Less molasses is present in refined sugar, giving it its signature white, crystalline appearance. The raw sugar is melted to remove these impurities and is essentially purified twice, resulting in a product fit for human consumption.

Refined sugar is also used in the food and beverage industry by manufacturers, but can also be bought over the counter for consumption at home. You can find out more about refined sugar and the sugar refining process in our blog.

white, refined sugar is the sugar most commonly seen in shops and restaurants

Brown sugar

What is brown sugar?

Brown sugar is essentially refined sugar with molasses added back in. Although molasses is already present in raw sugar, the other impurities that it comes with must be removed for the sugar to be fit for direct human consumption. That is why, odd as it may seem, brown sugar is refined and then turned back into a product containing molasses.

There are different varieties of brown sugar, including muscovado, demerara and just plain old brown sugar. For each variety, there is a dark and light brown version – the darker the sugar, the more molasses is present. Molasses is the ingredient that gives dark brown sugar its rich moistness.

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White sugar

What is white sugar?

White sugar is another name for refined sugar. The second stage of the sugar refining process is what gives it its white, crystalline appearance. There are different types of white (refined) sugar, such as caster sugar, granulated sugar and screened sugar. The main difference here is the size of the sugar granules – granulated sugar is coarser than caster, and screened is even finer than caster. You can read more about the sugar refining process, in this step by step guide.

Cane sugar

What is cane sugar?

Cane sugar is sugar from sugar cane – one of the two natural resources from which sugar can be extracted. Sugar cane is commonly found in locations that experience hot weather conditions, including some of the world’s top 10 sugar producers Brazil, India, Europe, China and Thailand. The sugar cane is crushed at a sugar mill, where its plant materials are separated from the sugar content. You can read a more detailed description of the cane crushing process in our blog.

Sugar beets in a field. Sugar beet grows in the ground and favours milder climates.

Beet sugar

What is beet sugar?

Beet sugar is produced from sugar beet, as opposed to sugar cane. Sugar beet grows in milder climates and can be found in some of the world’s top 10 sugar producers like Europe and parts of the United States. Like sugar cane, the sugar beet has to be processed to extract the sugar from the plant. Rather than being crushed, sugar beet is sliced into ‘cossettes’ – essentially thin slices. The beet is then soaked in hot water and the raw sugar juice is sent for purification. You can read more about the beet production process in our blog.

How to classify sugar: Harmonized commodity description and coding systems (HS)

In addition to the main attributes used to categorise sugar, which we explain in more detail below, there is also an internationally recognised system used to classify commodities called the Harmonized commodity description and coding systems (HS). It’s useful to know about this in addition to more sugar-specific sugar categorisation.

The harmonized system (HS) uses a six digit coding system to sort over 5,000 products. Sugar is grouped in section 17, within which each type of sugar has its own unique code. The six digits can be broken into:

First two digits – identifies the section

Second two digits – identifies the groupings within a section

Third two digits – even more specific detail

For example, 1701 is the general HS for cane sugar. 17 tells us it’s a sugar, and 01 tells us it’s cane sugar in pure, solid form. 170114 denotes other types of cane sugar.

Sugar quality process

Sugar is tested in many ways to validate its quality. These tests are according to a standard set of quality parameters that are important in demonstrating to potential buyers if the sugar meets the required standard. Sugar quality is important because it impacts the extractable sugar – the amount of sugar that can be extracted from the milling or refining processes.

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) measures the purity of the sugar, with the sucrose content of the sugar provided as a mass percentage. It is the main standard that is used to determine the quality of the sugar, and for sale to go ahead there is often a polarisation specification that must be met. A sugar crystal is very close to 100% pure sucrose, which is why pol is a useful measure. 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.) Polarisation 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. This makes sense when you think about the fact that molasses and other impurities make the sugar darker in colour, and therefore more difficult for light to pass through.

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. Different colourants respond differently to the refining process, which is why colour is an important differentiating process when refineries are purchasing raw sugar that they want to turn into refined 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 (IU) 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.

Raw sugar being loaded onto a ship. You can see the colour is quite dark, due to its unrefined nature.

Sugar quality: ash

Ash refers to all the inorganic components that are naturally present in the cane or beet. It is present in cane juice, and is carried over in a smaller amount into raw sugar. Ash is made up of both soluble and insoluble compounds and can be determined by the conductivity of the solution. It is quite complex chemistry, but essentially a conductance meter is used to measure the soluble, inorganic compounds present in the sugar. If there is a high ash content in raw sugar, higher refining costs will be incurred as it will take longer to purify and there will be less yield.

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Sugar quality: moisture

Reducing moisture in sugar is very important, as sugar is hygroscopic (meaning it absorbs moisture from the air) and can ‘cake’ if it becomes too moist. Caking occurs when sugar becomes too moist, and the granules become solidified. If caked, sugar is deemed less valuable because it is no longer usable across a wide range of applications. This can have damaging implications in the world of sugar trading, so it is essential that moisture is taken into account before sale and transport. 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%.

Sugar quality: crystal size and uniformity

Crystal size, also known as ‘screen size’, is important because is the sugar has irregularly sized grains the refining process is hampered. It is therefore important to refineries to know that the sugar has met a certain screen size, and important to mills that they are able to produce uniform sugar that is able to fetch a profit.

Sugar quality: filterability

Filterability can be defined as how easy it is to pour sugar through a porous material, is compared against a pure sucrose solution of the same concentration and temperature. This process identifies the extent to which the sugar has been carbonated. It’s an important factor for refineries, because sugar with low filterability reduces the throughput of the refinery – leading to financial losses over time.

Factors impacting sugar quality

There are a range of factors impacting the quality of sugar. Some quality issues stem from the farming stage, where cane or beet is exposed to different levels of nitrates, amino acids, potassium and sodium. There is a fine balance: yields increase with an increased nitrogen application, but the total recoverable sugar is reduced as nitrogen increases. The optimum amount of nitrogen is in itself dependent on the soil, fertilisation and previous crop. Phosphorous deficiency can impact juice purity, and potassium and sodium decrease the extraction. The milling and refining processes are also defining factors, as they require precise temperature control and equipment maintenance.

You can find out more about the production and distribution of sugar in the sugar section of our blog. We cover the milling and refining processes, cane sugar, beet sugar, the history of sugar and the top 10 global producers.

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