(Freeze-)Drying of Foodstuffs

The dehydration of foodstuffs with zeolite is an alternative to freeze-drying.
Zeo-Tech is seeking a licensee for this application of zeolite/water technology.

Study: Adsorption dehydration on an industrial scale

Zeolite/water technology is eminently suited to the energy-efficient dehydration of water-bearing substances. Besides saving energy, this method also has the advantage that it works without any significant loss of aromatic substances.

Conventional dehydration

In the manufacture of instant coffee, for example, the following two processes are currently used:

  • In the freeze-drying process, the watery extract is frozen at low temperatures (– 40 °C) and dried in a vacuum. The energy input in this process is very high.
  • In the spray-drying process, the watery extract is forced through nozzles at high pressure and sprayed in the form of ultra-fine droplets. Hot air is blown through the cloud of droplets, which then dries. What remains is coffee powder. However, it contains fewer aromatic substances than is the case in the freeze-drying process.

Dehydration by means of adsorption of water vapour by means of zeolite

In dehydration by adsorption, the gaseous aromatic substances which escape from the product being dehydrated are not removed from the drying chamber. They remain in the drying chamber and are put back into the product that is being dehydrated by means of a forced flow. A balance is therefore struck between the vaporising substances and those being readsorbed. This process is made possible by the selective adsorption properties of the zeolites chosen especially for this application. Dehydration by the adsorption of water vapour in zeolite works as follows:

  • For the dehydration process, the extract to be dehydrated is placed in a thin layer on a kind of tray and enclosed in a vacuum-sealed vessel. An activated, dry charge of zeolite in the vessel acts as an adsorber for the water vapour. Once the air has been evacuated from the system, the zeolite begins to absorb water vapour, thereby extracting the water from the raw material.
  • The crucial advantage of this method is that only water vapour is adsorbed in the zeolite. The aromatic substances remain in the gas chamber and are readsorbed by the dry raw material.

Results of experiments

Extensive dehydration tests for the dehydration of coffee were carried out on a laboratory scale using a test facility, whereby very good results were achieved under the following conditions:

  • Extract temperature below 60 °C
  • Dehydration time 18 mins.
  • Thin layer of extract on tray (approx. 600 g/m² )
  • Solids ratio in starting product 60 to 72 %.
  • Solids ratio in end product 96 %

Dehydration on an industrial scale

The following drawing shows an industrial coffee dehydration plant.

Zeo-Tech is seeking a licensee for this application of zeolite/water technology.