Food drying technology turns the next corner

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Related tags: Food

With 25 years of engineering and development work under his belt
Jim Schak has become such an authority on food drying technology
that he lectures on the subject at university. Here he discusses
the latest trend towards two-stage fluid bed drying and its

An essential element in the primary stages of food processing is the washing and drying of foods and ingredients. Washing is a relatively straight forward process, but drying, on the other hand, is a far more complex affair, requiring more technologically advanced machinery and equipment.

Working as an engineering manager for the Witte company, Washington, New Jersey, Jim Schak has been the brain-child behind some of the biggest advancements in the drying process in recent years. And the product of his toils can presently be found in some of the big food production operations of luminaries such as Nestlé and Kraft.

Schak explained that there are three main areas in which he has advanced drying machinery: "The first is air recirculation, which concentrates on improving the drying efficiency of the machinery. Secondly there is multiple stage drying, and thirdly there is predrying technology, which is especially designed for food stuffs that are sticky.

"Air recirculation allows for 25 per cent of the total heat to be reused. On top of that it is less expensive to fit because there is less duct work and it can also increase production. However, there is the drawback that this system may require a bag collector, which, for the purposes of food production, is less sanitary."

Multiple stage drying is a good solution for foods and ingredients which are of a higher quality or a fragile composition.

"A major tendency is to use a secondary fluid bed dryer to achieve better product quality and energy efficiency. A single spray dryer is very expensive, with poor efficiency, but if this is complemented by a fluid bed dryer, it means that the spray dryer will not have to be worked so hard to achieve maximum efficiency.

"The fluid bed dryer is beneficial because it reduces the evaporative load of the spray dryer which in turn allows a lower outlet air temperature and better productivity because the feed rate can be increased to decrease the outlet air temperature. However, the downside of this technology is the added cost of the secondary dryer."

Schak's most recent project, and perhaps the one he is most proud of, is the predryer vibrating fluid bed technology. This was developed to handle sticky foods, which are traditionally more difficult to dry off.

"Existing belt drying technology for these kinds of products was inefficient because it didn't manage to dry the foods off properly, which caused all kinds of problems with the product quality. Sugary foods, for example sesame seeds and raisins, would not dry off properly, then they'd stick to the conveyor belts and burn when they were dried repeatedly.

"In order to minimise this problem a predryer fluid bed section was developed to pretreat the sticky foods. The concept required that small amount of Teflon-coating was used on the deck of the belt. Combined with a high velocity and low temperature this means that this pre-dryer section removes the sticky moisture on the outer layer so the material can enter the larger section without sticking."

All three of these drying technologies have been developed to increase drying efficiency, save on production costs and increase productivity. Although each solution costs more than the conventional drying systems, Schak is convinced that in the long run the increased efficiency and reduction in running cost can only bring benefits.

"What's more these technologies are definitely becoming far more popular within the industry," said Schak. "There is now a distinct trend towards two stage drying - as opposed to one stage drying - because production operations are becoming increasingly aware of the benefits they carry."

Related topics: Food Safety & Quality

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