The IQF tunnel which literally "shock freezes" food items (normally sea foods) to minus 40 degrees Celcius in a matter of few minutes, thus effectively cutting out bacterial action. The product also does not lose any of its moisture or original tissue structure on thawing, hence retaining its freshness even after, say, six months.

At a live demonstration of this new freezing technique at IIT, Powai, the Dean (Planning) Professor K G Narayankhedkar, said: ``Presently, the IQF Tunnel technique is best suited for freezing marine products such as fishes. However, it becomes rather expensive to use it on a mass scale for other food items such as potatoes and onions.''

The IQF process using liquid nitrogen is categorised under `Cryogenic Freezing' (kryos means very cold;genes is to produce). In this process, the sea foods are frozen individually by direct contact with a spray of liquid nitrogen making the surface temperature as less as -40 degrees C. Compared to the IQF process, the minimum temperatures reached in a normal home refrigerator used by housewives is only -10 degrees C.

``While the IQF Tunnel process is much more effective than other existing IQF techniques, the only disadvantage here is that it requires large amounts of liquid nitrogen,'' said Prof Narayankhedkar.

A detailed survey recently conducted by the Tata Consultancy Services had stated that apart from the global acceptance of its technical feasibility, a large number of fish processing units are expanding their capacities and many new companies are coming in the field.

Based on these requirements, IIT developed the IQF tunnel which has a freezing capacity of 100 kg per hour, and energy consumption of 2 kilowatts. The total weight of the tunnel is 600 kgs and is 3.2 metres long. The consumption ofliquid nitrogen comes to 1.2 kg per kgs of the product.

The IQF tunnel mainly consists of a conveyor belt on which the food is placed at one end of the the tunnel. Once inside the tunnel, the product is first pre-cooled with nitrogen vapours and then sprayed with liquid nitrogen to supercool the food item.

At the live demo at IIT a soft fish like a pomfret became as hard as stone within seven minutes once it comes out of the tunnel as it has fully received the cryogenic shock for longtime storage. After this, the fish can be kept at a normal freezing temperature of say -20 degrees C.