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Granulating High Viscous Melts in the Food Industry

| By Miles Farnsworth

Ulrich Nanz, Sales and Marketing Director at industrial process solutions company IPCO, describes the particular issues involved in granulating high viscous melts used by the food industry and explains how Rotoform technology has been tailored to overcome these challenges.

Food processing – like that of chemicals, cosmetics and pharmaceuticals – often involves combining a number of ingredients to create an end product. Mass production means doing so using industrial quantities, usually requiring materials to be converted into a form that is easy to reprocess.

One of the most widely used approaches to this is granulation, the forming of pastilles suitable for downstream transportation, storage, handling and dosing. For the food sector, industrial ingredients frequently converted into pastilles include emulsifiers, chocolate and edible fats.

The principle is simple: melt the product, form it into droplets and cool it down into solid pastilles. The reality of course is more complex, requiring precision engineering and strict control of everything from temperature to humidity. And there are qualities that make certain product types even more challenging. For the food industry, these include caramel and chewing gum resin, both characterised by their high viscosity.

Caramel, a mixture of butter and sugar, is used often as a colouring agent in beer and colas. Chewing gum resin is an umbrella term for the gum base recipes used by different manufacturers, many of which incorporate rosin, a natural resin obtained from pine trees and other plants. In both cases, the product is highly viscous: typically between 5 000 – 8 000 mPas for caramel and up to 15 000 mPas for rosin.

In order to appreciate the challenges presented by these products, it is first necessary to understand how ‘standard’ food products are handled.

Granulation directly from the melt

One of the most commonly used processes for the granulation of food products is IPCO’s Rotoform 4G. This produces pastilles of highly uniform shape, stability and quality – properties that can be reproduced again and again – in an environmentally friendly manner.

A pump delivers the molten product from a vessel or pit to the system via heated pipes and a filter. The Rotoform itself consists of a heated cylindrical stator – which is supplied with liquid product – and a perforated shell that rotates around the stator. Drops of the product are deposited by the nozzle bar across the whole operating width of a continuously running stainless steel belt.

A system of baffles and internal nozzles built into the stator applies uniform pressure across the belt width, delivering an even flow through all holes of the perforated rotary shell. This ensures that pastilles are of a uniform size, from one edge of the belt to the other.

The rotational speed of the Rotoform is synchronized with the speed of the belt to allow a gentle deposition of the liquid droplets onto the moving belt. Heat released during cooling and solidification is transferred via the steel belt to cooling water sprayed underneath. This water is collected in tanks and returned to the water recooling system; at no stage does it come into contact with the product.

The result is a high quality pastille of consistent size and shape. Their free-flowing form makes them ideal for handling, blending, storage and further processing.

Combining hygiene and high feed temperatures

Rotoform technology has evolved over many years to meet different market requirements, and this has led to the development of a range of application-specific systems including the 4G food (FD) model, a system designed to meet the high standards of hygiene necessary in the food sector, and the 4G high temperature (HT), for products that need a high feed temperature (up to 285 °C).

The high viscosity – and therefore the need for a high feed temperature – of caramel and chewing gum resin requires a system that combines the features of both the FD and HT models.

All materials that come into contact with the product must be of food-grade design (FDA compliant) and capable of withstanding high temperatures. The system as a whole must comply with the highest standards of cleanliness and hygiene. And features must be incorporated to avoid the risk of humidity, as unwanted moisture could affect the composition of the product. Another reason for maintaining a dry atmosphere is that moisture can transfer impurities (i.e. dust) from the air to the product.

From mixing and feed to cooling and cleaning

The design of the system begins with the feed to the Rotoform and this is driven by the need for a high and very specific temperature. High viscous products are sticky and difficult to handle.

However, it is not simply a matter of heating the product until it melts. As mentioned earlier, manufacturers use different recipes for chewing gum resin. Some need a feed temperature as high as 270 °C others are fed at 220 °C or 180 °C. And it is crucial to use the correct temperature. Heat it too high and/or for too long and the rosin will discolour and cause the chewing gum to taste bitter.

This means gentle handling of the product as it is only heated to the temperature at which it will be fed to the Rotoform. Thermal oil provides the necessary heat and the temperature of the product can be controlled and adjusted quickly and accurately, allowing optimum feed temperatures to be set for different products.

After the product has been deposited onto the steel cooling belt, some product residuals could remain to the outer shell. A heated refeed bar forces this product back into the Rotoform and keeps the outer shell clean, essential for sticky, highly viscous products.

The length of the cooler is determined by the temperature of the product: the higher the feed temperature, the longer the cooling line. A combination of different temperature zones can be used to meet specific cooling requirements. Once the heat has been transferred from the product to the cooling water – via the steel belt – the water is collected and returned to a chiller unit for re-use. This environmentally-friendly closed-circuit system requires only minimal make-up water.

As mentioned earlier, it is extremely important to avoid the development of condensate that could affect the quality of the product so the system also incorporates special air conditioners to keep the air dry.

Ease of cleaning is key to the design food-grade processing systems and even more so with sticky materials, where cleaning requirements are intensified. Lines used for the production of caramel can be cleaned using hot water; for the production of resin cleaning agents suitable for food processing must be employed.

In-line cleaning solutions can incorporate an oscillating knife at the discharge end of the steel belt cooler or washing device for the steel belt, and cleaning devices are also available for the dropformer. The design of the Rotoform 4G allows the unit to be moved to its service position at the touch of button. Solutions can also be provided for cleaning the upstream pump and pipework.


IPCO’s process understanding has enabled the development of a granulation solution that combines the qualities of its food-grade and high temperature Rotoform systems. Suitable for extremely high viscosity food products requiring very high feed temperatures – such as caramel and chewing gum base – it delivers high quality pastilles with no risk of off-spec material or thread formation.