Ice creams! A dessert that we all are fond of .Well we all have that one favourite ice cream or kulfi which makes our summer beautiful. Its not about only ice cream , while going to grocery shop for purchasing our daily use food products we see lot of frozen products kept in the freezer. Noways working people hardly get time to purchase fresh fruits and vegetables , in that way frozen vegetables (example-frozen peas) have made a great impact in their lives. So, have you ever thought which process is involved in the production of frozen products. The answer is “freezing”. So,let’s discuss about it and understand the difference between fast freezing and slow freezing.
What Is Freezing?
Freezing is the unit operation in which the temperature of food is reduced below its freezing point and a proportion of water undergoes change in state to form ice crystals.
Freezing is the oldest and most widely used preservation method.
Advantages Of Freezing
- There is no as such loss of nutrients, moreover texture and flavour is also retained by freezing.Thus frozen foods are better nutritionally and organoleptically.
- The low temperature inhibits the microbial activity and some enzymatic reactions.
- The shelf life of food products increases by freezing.
The Freezing Process
The freezing process occurs in two successive steps, i.e, ” NUCLEATION” and “CRYSTAL GROWTH”.
- Before ice can form ,a nucleus or seed is required upon which crystal can grow.The process of producing this seed is termed as nucleation.
- A nucleus is a site from which ice crystal starts to grow and hence cover all over the surface to freeze it.
- It is the critical step that results in complete phase change.
- Nucleation can be of 2 types-homogeneous and heterogeneous. Homogeneous nucleation occurs when water is free from impurities and heterogeneous nucleation (catalytic nucleation) occurs when water molecules aggregate in crystalline arrangement on nucleating agents such as active surfaces, this type of nucleation predominates in food systems
When a stable ice nucleus is formed after that crystal growth occurs. Crystal growth is not instantenous ,it is controlled by rate of removal of latent heat during phase change as well as rate of mass transfer in case of solutions.
Difference Between Fast Freezing And Slow Freezing
Slow freezing kills only few microbes and forms large ice crystals thus causing mechanical damage to the cells but in case of quick freezing, it kills all the pathogens and maintain uniformity in extra or intracellular water and form small ice crystals which leads to less damage to the cells. But there is one major disadvantage of fast freezing and that is large investments for deep freezer, and moreover it is energy intensive process which is not in slow freezing. But above all we can say that “fast freezing is better than slow freezing”.
Physical and chemical properties in freezing by Noemi Zaritzky