The process of freezing a food product occurs in three stages.
In the first stage, the temperature is reduced to freezing point. Then the water contained in the food product turns to ice (also called the latent heat phase) and finally in the third stage, the temperature is reduced to the final storage temperature (typically -18 °C).
When the freezing process is slow, large ice crystals form destroying cell structure, damaging the food product and compromising its quality in terms of freshness, taste and preservation.
During slow freezing methods, the free water around the food's cells is the first to crystallise.
As son as some of the water starts to crystallise, equilibrium is destroyed and the water within the cells food begins to migrate out of the cells walls, destroying the cell itself. The longer the freezing time, the greater is the number of destroyed cells.
Subsequently, the ice crystals become so large that the cells are completely destroyed, this leads to a decrease in product quality and high water loss when the product is re-heated or thawed.
Thus, the faster the rate of freezing, the better the quality of the frozen product. Using the cryogenic deep-freezing process, water on the inside and outside freezes at the same speed, ensuring the structure of the food is maintained along with its freshness, flavour and texture - as if it had never been frozen.
TECHNIQUE USED FOR SAMOSA PRODUCTION
For production of our Samosas we decided to use cryogenic deep-freezing using liquid nitrogen. Nitrogen (N2) is an inert gas, i.e., is not reactive, has no odour or flavour when stored under pressure and at a very low temperature (-196 °C) is in liquid form. When this form of liquid gas comes into direct contact with warmer products it vaporises and absorbs a large amount of heat and simultaneously cools the products. The gases obtained after vaporisation are also used to remove heat from the surfaces, before being released safely into the atmosphere, allowing the freezing equipment to operate very efficiently. This method, known as cryogenic freezing and cooling, has been in industrial use for over 40 years and is well known for ensuring high-quality frozen or refrigerated foods.
Information courtesy of:
LINDE Sogás, Lda.