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 | | SPRAY DRYING (INTERNATIONAL FOOD INGREDIENTS MAGAZINE: APRIL/ MAY 2008) | | | CMP | | 19/05/2008 | | | Ian McMurray looks at the many advantages of spray drying
and considers whether this long-popular technology has a future
in today’s changing market
What do prosciutto, raisins and stockfish all have in common? Simply, they are foods that are preserved by drying – ham, grapes and cod, respectively. Drying is one of many methods used over the years to extend the life of foodstuffs – think smoking, think pickling, think freezing. Today, those have been augmented by pasteurisation, canning, additives and irradiation, for example – but traditional methods persist.
One of those traditional methods is of particular interest to food manufacturers because its benefits extend beyond mere preservation. Suppose that not only could this method help to prolong shelf life – but also make foods easier to transport and process, and help make them more convenient. Even better: suppose the process could readily be called natural? And: supposing it facilitated new food concepts?
The process is, of course, drying. The food and ingredients industry today uses both freeze drying and spray drying, but the underlying requirement – removing the water on which decay organisms thrive – is the same. Today, however, the drivers behind drying are, less to do with the need to preserve foods (many of the foods that are spray dried – such as coffee, for example - are not susceptible to bacteria): the drivers are ease of processing, consumer convenience and innovation. That said: spray drying is widely used in the dairy industry, where shelf life is a concern.
What exactly is spray drying – and what is it good for? As the name suggests, it is a process that takes a liquid that contains solid matter (often referred to as a “slurry”) and, in effect, turns it into a solid by removing water. Typically, the resulting solid would be in particle or powder form. Perhaps its primary attraction is the substantial reduction in weight and volume from the slurry to the powder form, making the end product easier to process, store and transport.
How does it work? At its most simple, the slurry is sprayed under high pressure into a heated chamber. The pressure causes the slurry to break down into droplets – and as these pass through a heated chamber, water is removed. In many processes, the remaining solid matter is collected as a powder as it falls to the bottom of the heating chamber.
Spray drying is a much more complex process than that – if only because of the number of variables that have to be considered. In some applications, for example, a nozzle is used to force the slurry under pressure into the heating chamber – there are many types of nozzle, each designed to deliver specific application characteristics. In other applications, the slurry is delivered to a rapidly-rotating disc which disperses the liquid around the chamber. It is primarily here that droplet size – and thus the physical characteristics of the final dried product - is determined. Rotary atomisation is often recommended because of its flexibility, its ability to handle high feed rates and the fact that it is less susceptible to blockage.
This approach, however, has not been favoured by UK manufacturer of powdered food flavourings, micro-encapsulated food flavourings and ingredients TasteTech, as managing director Janis Sinton explains. “We opted for a nozzle dryer because of its ability to produce higher density, coarser products which we believe are better suited for the flavouring industry,” she says. “Nozzle atomisation produces a better emulsion which aids the encapsulation process, retaining more volatiles and producing better quality flavourings.”
Heating is another variable. Air is typically used, heated directly or indirectly with gas, or with steam, or with a thermal fluid. “Spray drying can also be carried out using nitrogen rather than oxygen,” points out Fabio Campanile, head of delivery systems at Swiss company Givaudan, which creates ingredients systems and flavours for beverages, sweet goods, savoury and dairy products. “That’s important for applications where the presence of oxygen may affect the finished product’s quality,” he adds.
Compared with other food drying methods, the advantages of spray drying are its relative economy - due to simple construction; that it does not damage food, as droplets spend a short time exposed to high temperatures; and that the resulting product exhibits high flowability, high solubility and high dispersability - making it easier to transport, store and process. It is also highly scalable.
“From our perspective,” notes Andrew Sainsbury, a director at TasteConnection which supplies a range of speciality taste ingredients including provenanced cheeses and a range of vinegars, “spray drying is the most economical way of drying products. It also allows you to co-dry products onto a carrier. Freeze drying is very good for whole products such as coffee, where there is a high solids content – but it is very costly.”
“The big advantages of spray drying,” adds Sten Warburg, deputy division manager, food and dairy division at spray drying systems company Niro A/S, “are that it is highly scalable, with the ability to evaporate over twenty tons of water per hour at the high volume end to very small, but equally efficient systems that might be well suited to lower volume, premium products; that it is very cost-effective; and that it allows manufacturers to perfect their products in terms of agglomeration, product structure and micro-encapsulation.” Size – in both directions – has characterised recent changes in spray drying: 20 years ago, a 5 tons/hour dryer was considered large.
“Whether you freeze dry or spray dry is largely about the nature of the feed material, and what the final product properties need to be,” says Gerard O’Sullivan, technical manager at international dairy processor and food ingredients group Glanbia Ingredients of Ireland. “Freeze drying is great for nutrients that are very sensitive to heat, but it is a very expensive plant and process, and plants are not only limited in scale but they are also typically batch-oriented. Spray drying, on the other hand, has a wide range of sizes and is continuous – and it is a relatively gentle process. However: it is comparatively more expensive than fluid bed, roller or attrition drying.”
So how does a manufacturer determine whether spray drying might be appropriate for a specific application? “Physical and chemical parameters will vary from one application to the next,” says Antoine Dauby, marketing manager at plant extract manufacturer Naturex. “It is very important to understand the properties of the liquid to be dried and the expectations.”
“It’s about matching the technical specifications of the product to the product to dry,” adds Mr Campanile, “and about the final physical form of the product which will, typically, be powder rather than granules.”
There is widespread agreement that freeze drying and spray drying do not compete: as Mrs Sinton points out: “It’s horses for courses.”
“Spray dryers require a large initial outlay. They are tall, and need a larger building than some other options,” says Mr O’Sullivan. “But if they are looked after and made from the right materials, they are not too expensive to maintain. The associated processes of mixing, pumping, evaporation and powder handling, however, are as complicated as any system. Cleaning is quite easy, and in many cases spray dryers operate for several weeks between cleans.”
“The lifetime of spray dryers is very long,” notes Mr Warburg, “because the number of moving or rotating parts is small compared with many other water-removing systems. Cost of ownership is relatively very low.”
But in an era when premium products are increasingly popular, where powders are seen as less attractive, and health is a priority, does spray drying have a future?
“Spray drying from our point of view is simply a means to an end - converting a liquid product to a powder in applications where the customer is unable to use a liquid in their application,” says Mr Sainsbury. “However, it is certainly true that the demand for more premium ingredients for use in seasonings has led to more different products being spray dried.”
“We see both trends – towards premium products, and towards healthier products - as opportunities, rather than as threats,” says Mr Warburg. He continues: “Spray drying can play a key role in the addition of functional ingredients such as Omega-3 and antioxidants.”
Mr O’Sullivan notes that spray drying has brought the nutritional qualities of milk to parts of the world where factors such as climate limit economic fresh milk production. “But the developed world is now benefiting too,” he continues. “The combination of ultrafiltration - which was originally used for whey processing - and spray drying makes it possible to deliver a more whole and pure native form of milk protein which we call Milk Protein Concentrates and Isolates: Glanbia’s Solmiko range.”
Both users and manufacturers of spray drying systems are bullish about their advantages. “With our purpose-built high residence time dryer and the introduction of new raw materials, TasteTech are now able to produce better quality flavourings which may be sprayed with a higher loading than was previously possible,” enthuses Mrs Sinton.
“The fact is that spray drying is cost-effective, and does the job well,” adds Mr Campanile. “Understanding material science and the behaviour of flavour ingredients with the carrier and the process are the keys to delivering a high quality end product. For Givaudan, like other companies, spray drying represents the most cost-effective solution for achieving that – and that’s why it is the success it is today.”
www.givaudan.com
www.glanbia.com
www.naturex.com
www.niro.com
www.tasteconnection.co | |
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