The importance of heat in glucose production

More than 15 million metric tonnes of glucose are produced globally each year for use in food and drink manufacturing, pharmaceuticals and cosmetics, textiles, adhesives, and many other applications. Heat is important at various stages of the manufacturing process, with each phase having specific temperature requirements. As a result, both corrugated tube and scraped surface heat exchangers are ideally placed to improve energy efficiency in glucose production.

The global market for glucose is worth around US$58 billion, with just under half of this used for food and drink production. By 2034 the market could be worth an estimated US$87.7 billion, fuelled by a move towards clean-label ingredients and increased pharmaceutical use (currently around 32% of the total market).

Material and uses

Glucose (dextrose) is a simple sugar (a monosaccharide with the formula C6H12O6) which is commonly formed through the hydrolysis of starchy products such as corn (maize), wheat, potatoes or tapioca. It is characterised by good solubility in water, high viscosity and good hygroscopicity. In human biology, glucose is the basic unit of energy and is involved in many processes. It occurs naturally in honey and fruits, such as grapes.

Although predominantly used as an ingredient and sweetener in food and drink manufacturing, liquid glucose is also widely used in a wide range of other industries and sectors. In pharmaceutical applications it may be used for binding tablets, as the base for cough syrups, and in IV drips. It is also used in leather tanning, textiles, paper manufacture, formulating adhesives, cosmetics, animal feed, biofuels, and tobacco processing.

Glucose for food use

Food-grade glucose must meet strict safety standards and has multiple uses in the food and drink sector, including acting as a sweetener, adding moisture, managing fermentation, providing readily consumed energy, preventing sugar crystallisation, maintaining texture and improving shelf life. From energy drinks to bread, sweets and chocolate to ice cream, fruit juice to cakes, wine to jam, glucose is one of the most common food ingredients worldwide.

Food-grade glucose is normally supplied and utilised in one of three forms. Anhydrous glucose is a fine white powder that contains no water molecules but is hygroscopic and prone to clumping. Glucose monohydrate contains around 9% water and has a more flowable, crystalline structure. Liquid glucose is a clear sweet syrup containing more water, making it easier to handle as a liquid or semi-liquid product. The sweetness and functional properties of glucose are determined by the dextrose equivalent (DE), a measure of how completely the starch was broken down the lower the DE, the more complex sugars may be present.

Although the names are often used interchangeably, pure liquid glucose may be different to glucose syrup, which can contain other materials and sugars such as fructose. Glucose syrup is often less sweet than liquid glucose but may have other practical benefits in terms of its use and handling.

The role of heat in glucose manufacturing

Heat is important at various stages of glucose manufacture, and each stage of the production process has specific temperature requirements (for example, the saccharification stage where the complex sugars are broken down into sucrose typically occurs between 55degC and 60degC). Moving beyond these specified temperatures can affect process yield and efficiency, and change the quality and purity of the finished product.

Most glucose production begins with cleaning, grinding and then heating the feedstock to break down intermolecular starch bonds in preparation for hydrolysis. Later on, dilute syrup is often evaporated to increase the concentration of solids before use or further drying and processing. Depending on the feedstock and production method, glucose syrup may also require pasteurisation or sterilisation before use in food, beverage or pharmaceutical applications. Heat exchangers can be utilised in all these stages, as well as for cooling product between stages or after final evaporation or pasteurisation. Using heat regeneration at the various production stages will also increase operational efficiency and reduce thermal energy costs.

The viscosity of glucose syrup and glucose solutions can vary greatly, and depends on a number of factors including temperature and concentration. Because of this, it is vital to choose a heat exchanger that can cope with the viscosity without fouling, while maintaining effective and thorough heat transfer. As an example, glucose syrup can have viscosities between 4,300 and 10,000 cP (mPas) at ambient temperatures, while dilute aqueous glucose solutions range from very fluid (just over 1 cP) to moderately viscous (~50 cP).

Choosing the right heat exchanger for glucose manufacture

Where glucose syrups and solutions require pasteurisation or sterilisation, a hygienic, stainless steel, corrugated multitube heat exchanger, such as the HRS MI Series, is ideal. The corrugated tube design increases heat transfer and efficiency compared to smooth tubes, but most importantly minimises fouling from the moderately viscous product. In the MI Series, the glucose solution flows through the interior tube, while the service fluid flows through the surrounding shell. Meanwhile, expansion bellows absorb the differential expansion rates between the two.

Where the process involves more viscous materials (for example, processing glucose syrups, or the concentration of glucose solutions via evaporation), then it may require the use of a scraped surface heat exchanger, such as the HRS R Series. Not only does this prevent fouling of the product on the tube surface and mixes the glucose throughout the process, helping to prevent crystallisation, but it also reduces the pressure drop along the length of the heat exchanger, reducing the energy and running costs associated with pumping.