JourneyJourney ofof MilkMilk Article –– FromFrom CowCow toto ConsumerConsumer Feature How is the milk that lands at your doorstep processed in a dairy plant? Here is an inside look into the processing of the world’s most ubiquitous B.S. BENIWAL & beverage. RENUKA MALIK digestibility of these nutrients present in Processing Milk milk, including proteins, fats and minerals Earlier, in India as elsewhere, milk giving is higher than vegetable proteins and fats animals like buffalo and goat were or inorganic mineral supplements. domesticated by families or groups of This nutrient richness and diversity does families. For some, it soon emerged as an OR most of us, the day starts with milk. not go unnoticed by some occupation – breeding and rearing Either milk bottles or packets land at microorganisms too, which also find it a animals and supplying milk to customers. Fyour doorstep or it means an early suitable medium for growth. These As the diversity of milk products and quality morning sojourn to the nearest dairy or microorganisms grow and secrete acids and safety concerns expanded, the scale booth. Humans have been using milk as a and other substances that coagulate the and technology used in dairy operations food since ages. From a physiological proteins resulting in the destruction of the also increased. perspective, milk is a secretion of the colloidal nature and the curdling of milk. Today, most cities in India have “milk mammary glands to nourish the newborns Fermented milk products like Dahi and schemes” that employ specialized dairy of mammals. It forms a complete food in yoghurt have therapeutic value as they technologists who subject milk to various their early life. It is an excellent promote the growth of desirable microbial dairy processes. A Dairy Technologist has combination of different nutrients populations in the intestines. to ensure that milk remains fit for human dispersed suitably in water. Milk is thus a source of different Milk contains milk fat, which is nutrients that need to be maintained in composed of various fatty acids and various products and under various furnishes all essential fatty acids to our processing conditions. Dairy Technologists body. Milk fat imparts a rich and pleasing view milk as an emulsion in which various flavour to the food items that it is present components are present in different in. Milk fat is a strong antioxidant and has phases. Fat and fat associated anticancerous effects. Milk proteins are substances are present complete proteins as they contain all in emulsion phase, essential amino acids required by the proteins are human body, and mend the wear and present in colloidal tear of our body. phase, minerals Milk is also a good source of different and sugars are minerals, particularly bone and teeth present in true forming Calcium and Phosphorus. It is a solution phase. good source of different vitamins also particularly Vitamin A. Moreover, the 19 SCIENCE REPORTER, JULY 2012 Feature Article Milk plants have immense capacity of processing large quantities of milk (Courtesy: Delhi Milk Scheme, Govt. of India) Above: Milk being packed in polyethylene packages (Courtesy: Delhi Milk Scheme, Govt. of India) Above extreme left: Dairy processes ensure that certain criteria of quality and safety are satisfied in the milk product (Courtesy: Delhi Milk Scheme, Govt. of India) Above middle: Inside a Milk Plant (Courtesy: Delhi Milk Scheme, Govt. of India) Left: Quality Control Tests being conducted (Courtesy: Delhi Milk Scheme, Govt. of India) SCIENCE REPORTER, JULY 2012 20 Feature Article Milk plants sell milk in poly Pasteurization & Homogenization packages that have information Recently, there has been some criticism that processed milk, particularly regarding the quality of the ultra high temperature pasteurization (used in the West) and homogenization (treatment at ultra high temperatures) affect the taste and smell of milk, as milk, date of packing and best well as destroy important nutrients such as amino acids. Homogenization, before use etc. by breaking milk into smaller globules that increase the surface area, makes consumption in a desirable state with its milk more prone to oxidation. Oxidized milk fats lead to a variety of oxidative maximum nutritive value intact. He or she stress-based diseases. These criticisms are being evaluated by further has also to see that the nutrients are scientific research, and dairy processes are being tuned in light of the conserved through the manufacturing and findings. transport of various milk products until their Pasteurization: The microorganism increases. The interactions become so high consumption. that had gained entry into milk may be that it does not allow the fat globules to The milk goes through several either pathogenic (disease causing) or separate out. Homogenization is generally processes that can be termed as “Dairy spoilage type. Pasteurization kills all used in reconstitution of milk and fat rich Processes”. Dairy processing is an industrial pathogens and most of the spoilage type products like ice cream, condensed milk, operation in which milk components are of microorganisms. For this purpose milk is sterilized flavored milk etc. Homogenized separated and re-constituted to produce heated to such a time-temperature milk does not stick to the container and desired milk products. From milking to combination that ensures destruction of gives a viscous appearance and rich consumption, milk may undergo a lot of even the most heat resistant pathogen. mouth taste. dairy processes depending upon the Mycobacterium (TB germ) is the most heat product desired. Let us look at some of resistant pathogen and it is taken as the Sterilization: When milk has to be these processes. index for deciding pasteurization stored for longer periods it must be free temperature. Pasteurization may be done from all types of microorganisms to prevent Cooling: Milk secreted in the udder by two methods – Low Temperature Long spoilage. Some types of microorganisms of a healthy animal is sterile. But as soon as Time (LTLT) or High Temperature Short Time are able to ward off unfavorable it reaches the teat canal a large variety of (HTST). Nowadays, the HTST method is mostly conditions by forming spores. These are microorganisms may gain entry into it. As used. After pasteurization, the milk must be thick-walled structures with minimum these microorganisms proliferate in immediately cooled down to five degree biological activities and thus dormant forms stagnant milk, their growth is prevented by Celsius or below so that the surviving of bacteria. Spores may not get destroyed immediately chilling the milk to five degree microorganisms do not multiply further. even by boiling of milk. They are destroyed Celsius or below. At this temperature, milk through sterilization, which is the process will retain its freshness for three to four days. Cream Separation: In cream of heating milk to 120 degree C for 30 Cooling in a dairy plant is done by the Ice separation, fat is removed from the milk minutes or 150 degree C for 2-3 seconds Immersion method (a can of milk is dipped by passing it through a cream separator in so that a shelf life of six months of milk at into ice and the milk is immediately chilled) which it is rotated at a very high speed room temperature is ensured. or using a Plate Heat Exchanger (milk is (around 8000 revolutions per minute) in thin chilled with the help of chilled brine films. Milk cream or fat, being lighter Fermentation: Some desirable circulating in alternate plates). (specific gravity 0.9), remains in the centre bacteria convert lactose of milk into lactic Standardization: Standardization is while the skimmed milk, being heavier acid and some other flavour-producing the process of increasing or decreasing a (specific gravity 1.036), goes towards the compounds and are helpful in producing particular constituent in milk or milk product periphery in the cream separator. The different products like dahi, yoghurt, kefir, so that it conforms to the desired industrial separated cream and milk are collected kumis etc. Conversion of milk into various or legal standards. For example, if milk has from different outlets provided in the cream cultured products by these bacteria is to be sold as buffalo milk, the minimum fat separator. known as fermentation and these products percent should be standardized to 6% for are known as fermented milk products. most of the states in India. Milk may be Homogenization: The fat in milk is standardized to Full Cream Milk; Toned milk, present in the shape of fat globules that Re-engineering Milk Double Toned Milk etc. Full Cream Milk are of different sizes. The size may range Since milk is a perishable product, it is should contain minimum 6.0% fat and from 0.1 to 22 microns and generally it is received – that is, subjected to various tests 9.0% Solids Not Fat (SNF) while Standardized from 2-8 microns. The fat globules being to ascertain its quality as it arrives. When Milk should contain minimum 4.5% Fat and lighter rise to the top and thus the fat the milk reaches the milk plant a grader 8.5% SNF. Toned Milk and Double Toned separates out, particularly in products that receives the milk and subjects it to “Platform Milk should contain minimum 3.0% Fat and are rich in fat. Homogenization is the Tests”. Platform tests are tests that are 8.5% SNF and minimum 1.5% Fat and 9.0% process in which fat globules are broken conducted to accept or reject a SNF, respectively. In dairy processing, low down mechanically to a size of about one particular consignment of milk. fat milk can be standardized to high fat micron. This leads to increase in surface They may be organoleptic, which are milk (and vice versa) by adding the area of the fat globule, thereby interaction conducted with the help of our sense required milk components in appropriate of the fat globule membrane with the organs like smell, visual appearance, quantities.