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Steam treatment of food products

Many food products need to be heat treated to make them suitable for human consumption. Steam is a well accepted medium to be used, because of its properties. Steam kills pathogenic bacteria easily, has good thermal properties, is inert (no oxygen) and clean. If steam is superheated, it becomes a gas and can be used for drying purposes as well. Hosokawa Micron offers several types of process equipment that use steam.

HSSP batch sterilization process

HSSP is a flexible batch sterilization process based on the Nauta® conical dryer design. It is especially suitable for the heat treatment of products like herbs, spices and teas.

Nauta conical vacuum dryer

The working principle of HSSP involves six steps before a product is sterilized. Raw material in big bags or sacs is unloaded manually in the Nauta sterilizer (step 1). All next steps of the HSSP process are fully automated. A recipe is selected on the control cabinet and soon after the treatment process is started. The sterilizer is put under vacuum, heat is added to the product via the wall of the sterilizer and the mixture is homogenized. Steam is injected for a very short moment to minimize the quality losses.

Next step is the post-drying step, in which the condensed water is evaporated at vacuum conditions. A cooling water condenser is trapping the evaporated water vapours and ethereal oil losses. The moisture level of the sterilized product sets the duration of the post drying step. In step 5, the product is cooled under atmospheric conditions. During this phase it is possible to reintroduce some oils to the product. The product is ready for discharge from the Nauta sterilizer. During discharge any lumps in powdery products are removed before bagging or loading in a container.

HSSP is a completely automated process in which each product has its own specific heat treatment. Cleaning in between batches is not necessary as the amount left in the sterilizer is minimal. It is easy to integrate with a batch traceability system such as SCADA.

Heat treatment and drying using a flash mill dryer

Another, totally different process is a continuous steam treatment process based on a Drymeister (DMR-H) flash mill dryer. It is a fast and energy efficient method conserving valuable nutrients such as vitamins and proteins.

Drymeister (DMR-H) flash dryer

Water is heated to generate superheated steam, turning it into an inert gas with drying and sterilization capabilities. During the flash drying process the temperature is maintained above 100°C to avoid any condensation in the system and to assure product quality. Wet product cakes originating from filter presses and centrifuges or product slurries are screwed or pumped directly into the flash dryer. The convective flash dryer is provided with a dispersion/milling section (for instantaneous drying of wet cakes or slurries) and a classifier in the top of the dryer (for control of particles).

Superheated steam is introduced in the bottom of the dryer, just below the dispersion section. The product cyclone which is installed after the flash dryer are separates dried product and superheated steam and discharges a dry and sterile powder. The superheated steam is then conveyed back by a transport blower and recycled to the super heater, for re-use in the drying process. Excess steam is purged out of the system and available as a heating source.

This flash drying process is efficient, very fast, sterilizes the product, is safe (no oxygen). There is no risk of a dust explosion, compliant with ATEX directives. Some typical products for which the Drymeister (DMR-H) flash drying system has been proven to be very suitable are starches, flours, calcium carbonate, fish and vegetable remains.

Pilot units of all systems are available for demonstration in the Hosokawa's test and development centre in Doetinchem, the Netherlands.

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