Pasteurisation of dried ingredients

The pasteurisation of dry ingredients requires specialised conditions, as traditional water/steam-based heating systems are not appropriate.

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It had long been assumed that dry food and ingredients, carried little risk with regards to food borne pathogens.

It is now clear, however, that whilst pathogens are unlikely to grow in dry products, if they are present they can often survive.

The system shown here is for decontamination of low moisture foods such as seeds, nuts and spices.

It incorporates electrical heating with superheated steam, followed by a drying step to remove moisture before packing. The system, developed by Revtech France, uses two spiral columns - the first for pasteurising and the second for drying.

The dry particles are moved up the pasteurisation spiral by vibrations that also help prevent the particles settling and scorching. The residence time and the spiral temperature can be varied, to deliver an appropriate heat treatment.

For pathogen reduction, superheated steam is injected into the spiral.

In other words, the pasteurisation spiral provides a controlled wet environment for the destruction of microorganisms.

Depending on the product, the process requires a drying or cooling step to lower the product's water activity to a level suitable for storage. So, as the product leaves the pasteuriser, it is passed through the drying spiral, again via vibrations, where cool, filtered air is blown on to the product to dry and cool it.

The pasteurisation spiral can also be used to roast or toast products such as nuts and seeds - a process which doesn't require steam addition.

The pilot facility shown is available for independent trials, to help companies establish the process parameters for their products.

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