Milk Processing and Storage Methods
The raw milk obtained from dairy animals is highly perishable and cannot keep for long even when the quality is high. Therefore, the milk has to be converted to more stable forms in order to increase its shelf life.
As mentioned before, milk is very versatile and can be processed and is indeed processed to thousands of products globally depending on different traditions, habits, and customs. This unit will discuss the most common products obtained from milk when it is processed.
Almost all the processing methods for milk have the common objective of extending its storage or shelf life. Therefore, processing results in the conversion of raw milk into other products.
Whole milk, once approved for use, is pumped into storage tanks or silos where it undergoes pasteurization, homogenization, separation, and further processing into different products.
Pasteurization or heat treatment involves heating every particle of milk to a specific temperature for a specified period of time and cooling it again without allowing recontamination heating it at 63 to 66 ◦C for 30 min or 72◦ C for 15 seconds.
These conditions provide fresh-tasting milk that meets the requirements for consumer safety. Higher heat processes, such as ultra-pasteurization (137.8◦C for 2 seconds) or aseptic/ ultra-high temperature (135 – 150◦C for 4-15 seconds) or sterilization (115.6◦C for 20 min), are used to extend the shelf life of refrigerated products or allow for storage at room temperature, respectively, but may impart a cooked flavor to the milk.
The fat in milk is in globules of non-uniform size, and the non-uniform size of the globules causes them to float, or cream, to the top of the container. Pasteurized milk does not necessarily need to be homogenized.
However, homogenized milk should be pasteurized to inactivate native enzymes (lipases) that deteriorate fat and cause rancidity, which results in off-flavors and reduced shelf life in milk.
Read Also: Understanding Milk Quality and 5 Quality Characteristics of Milk
The purpose of homogenization is to reduce the milk fat globule’s size, which allows them to stay evenly distributed in milk. Homogenization is a high-pressure process that forces milk at a high velocity through a small orifice to break up the globules.
The result of homogenization is the creation of many more fat globules of a smaller size so that the fat is dispersed evenly throughout the milk, stopping the fat from floating to the top of the container to obtain a more uniform consistency.
Separation involves spinning milk through a centrifuge to separate the cream (fat-containing a portion of milk) from the milk. After separation, the cream and remaining milk are remixed to provide the desired fat content for the different types of milk being produced.
For whole milk, the cream is reintroduced until the fat content reaches 3.25-4%. For low-fat milk, the fat content is 1%. For skim milk (sometimes called solids non-fat milk) the fat content is .05%.
Milk that has gone through pasteurization and homogenization can be processed into many different forms such as whole (full cream) milk, low-fat (defatted) milk, skim milk, fortified milk (low-fat milk fortified with vitamins A and D), flavored milk (with chocolate, vanilla, etc.), condensed milk, evaporated milk, powdered (dried) milk, and filled milk (animal fat replaced with vegetable fat).
Different milk products are also produced with specific processing procedures such as yogurt (curdled milk), ice cream, butter, cheese, casein (milk protein), lactose (milk sugar), whey (liquid remaining after milk is curdled), and whey powder (dried whey).
In conclusion, the versatility of milk in conversion to many different products all over the world makes it one of the most important food sources globally. Focusing on ways to improve the quality of milk products available locally in various areas could improve the well-being of those people most vulnerable nutritionally.
Read Also: Guide to Milk Production, Composition, and Nutritional Value of Milk
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