Cheese Fermentation and its Details
Cheese can be defined as a milk product that is obtained by coagulation of milk protein called as casein. The milk protein casein is coagulated by adding a rennet enzyme. The milk used for cheese manufacture may be skimmed milk or full cream milk. There are various types and different flavours of cheese made by various countries.
Image showing different types of cheese
Manufacture of cheese is generally divided into five major steps
- Control of milk Properties.
- Coagulation of milk.
- Separation of curd from whey.
- Cheese ripening.
- Cheese packing.
Flow chart of Important Steps in Cheese manufacture
1] Control of milk properties
The important factors of milk that can affect the quality of cheese are biological, physical and chemical properties of milk. So it is important to control these properties.
a] Biological properties of milk
- Milk of good quality is used for cheese making. Milk with low number of bacterial count is used. If the milk with high microbial count is used it may result in development of undesirable flavour. This problem occur during cheese production.
- Secondly milk contains some enzymes that are introduced in milk by mammary tissues of milking animal as well as the microflora present in the milk also release some amount of enzyme this enzymes contaminate milk. The enzyme that occur naturally in milk are amylase, protease, lipase, peroxidase, catalase.
- The biological properties of milk can be controlled by certain treatments like pasteurization. Pasteurization treatment is given to milk to reduce the number of microflora of milk. In this process milk is treated at 72 ° C for 15 seconds or 63 ° C for 30 minutes.
- Here hydrogen peroxide treatment is also given to milk to reduce the number of microflora.
b] Physical properties
- The milk may contain some suspended suspended things like extragenous material, leucocytes and particulate matter.
- Physical properties of milk can be altered or modified by using techniques like homogenization, clarification, filtration, centrifugation and vacuum treatment.
- Clarification of milk is carried out by removal of suspended particles in milk, removal of leucocyte and particulate matter.
- The suspended particles whose density is more than milk are removed by centrifugation process.
- The volatile odour of milk is removed by using Vacuum pasteurization.
c] Chemical properties
- The calcium present in the milk slowly becomes soluble and thus it cannot help in formation of firm curd. Fresh milk with low calcium content may need addition of calcium chloride in concentration of 0.02 %. The calcium chloride is added in milk after the process of pasteurization.
2] Coagulation of milk
In manufacture process of cheese the milk proteins are coagulated to form a solid curd. In milk the protein casein is around 82 % and 18 % is whey protein. In the curd formed after coagulation milk contains fat globulins, water soluble material and water. Coagulation of milk can be done by two ways:-
- Coagulation of milk by using Lactic starter culture – The milk is acidified by fermentation of lactose to lactic acid by using some bacterial cultures. The bacterial cultures used in coagulation of milk are Streptococcus cremoris, Streptococcus lactis, Streptococcus thermophilus, Lactobacillus bulgaricus and Lactobacillus helveticus. The bacterial culture is mixed properly with milk till acidity reaches to 0.17 to 0.2 % and then the coagulation enzyme are added in milk.
- Coagulation of milk by using Enzyme – A number of different enzyme preparation are used commonly to clot milk. Enzyme like rennet, porcine, pepsin, and protease from selected micro-organism are most commonly used.In manufacture of cheddar cheese the most commonly used enzyme is rennet enzyme. Rennet enzyme coagulates casein in 20 to 40 minutes. Casein protein gets coagulated at its isoelectric point at pH OF 4.7.
3] Separation of Curd and whey
Curd is a coagulated part the solid part formed after coagulation and whey is the water and water soluble part. Now we have to separate the curd from whey. The separation of curd and whey is done by heating, decreasing pH, physical disruption and manipulation of curd. The whey is separated from curd by many different techniques like partial dehydration of water. The curd and whey is transferred from cheese large vats to a cooling table containing screen.This screen allows the whey to drain and traps the curd. This curd further undergoes ripening process.
4] Ripening of Cheese
Transformation of elastic and chalky curd with an acidic flavour to ductile full flavored cheese can be accomplished by proper cheese ripening. During cheese ripening process various changes in physical, chemical and microbial characters takes place. In this process there is breakdown of proteins, carbohydrates, lipids, fats and sugar which are released by micro-organism and enzyme. The breakdown of this product results in contribution of flavour and texture to the cheese. The development of flavour and texture of cheese also depends upon pH, salts, temperature, humidity and composition of cheese. Further this curd is cut by using knives, steel frames and the curd is cut into small cubes. In this process of cheddar cheese formation the acidity of the curd is increased up to 4.7.
5] Cheese packing
Cheese is normally packed with a protective coating at a particular stage of ripening. The coating of cheese may vary from vegetable oil to special plastic films. The cheese is cut into rectangular form and coated with a plastic film. Cheddar cheese is pressed in large cylindrical blocks and due to pressing compact cheese blocks are formed,packed and sold in the market.
Flow Chart of Cheese Fermentation Process