‘Food,’ is probably only four letters word that ‘whet’s our appetite’ like no other. Our food, in fact, is no longer our basic need, but it has become our style statement, there are more ‘food’ channels in the world today, than ever before, and being a ‘foodie’ is an accolade for food lovers.
Apart from food for human consumption, Commerce also demands that food be preserved for days together. Modern hotels, for instance, make arrangements to deliver exotic cuisine across oceans, and in Medicine, sending a ‘well preserved’ serum from one part of the world to another, would save lives. ‘Preserving food preserves life.’
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How to Freeze dry food
Some of the recent methods to answer How to freeze dry food are Refrigeration, Freeze – Drying, Canning, Salting, Pickling, Smoking, Pasteurizing and Fermentation. The basic scientific concept in all these types of preservation techniques involves slowing down the action of bacteria and preventing new one from forming.
There are four steps in the Freeze-Drying process; Pretreatment, Freezing, Primary drying and Secondary drying –
The Pretreatment process involves; increasing the solution phase concentration or formulation to preserve the product appearance and stabilize the reactive products, increase its surface area and decrease the solvents.
The Freezing process is often carried out in a freeze-drying machine, using mechanical refrigeration, menthol, dry-ice or liquid nitrogen. The product is rapidly cooled below its ‘triple point,’ in order to enable sublimation below the ‘eutectic point’ of food and to prevent ice crystal formation, between -50 and -80 degree Celsius.
Primary drying means reducing the pressure to a few mili-bars and heating through conduction or radiation, to enable up to 95% of water to sublimate. The pressure is controlled by applying a partial vacuum, and a cold condenser chamber is provided for water to re-solidify on.
Secondary drying removes unfrozen water molecules; its effectiveness is governed by the products’ adsorption isotherms. Here the temperature is raised above the Primary phase, to break any scientific reactions between water molecules and frozen material. The pressure is lowered to aid desorption.
Once the Freeze-Drying process is complete, vacuum is reversed using nitrogen gas, before the product is packed.
That’s it. This is how to freeze dry food with advance technology.
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