This page describes the various operations used to produce beverage milk. The course covers the legal definition of liquid milk, standardization, pasteurization, homogenization, vitamin fortification, and special milk drinks such as lactose reduction and protein fortification.
Definition of liquid milk
Liquid milk is an industry term that refers to milk processed for beverage purposes.
Milk obtained from the complete milking of one or more healthy cows, containing a small amount of colostrum. The milk used in the final packaging form of the beverage shall be pasteurized or ultra pasteurized, and the solid content shall not be less than 8.25%, and the milk fat content shall not be less than 3.25%. Milk can be obtained by separating part of the milk fat or adding cream, whole milk powder, skimmed milk or skimmed milk powder. Milk can be homogenized. "Milk solids are the non-aqueous components of milk - protein, lactose and minerals. Sometimes, the combination of protein, lactose and minerals is called solid, not fat content, and if fat is included, total solid content.
The fat content in milk varies with breeds (cattle, sheep, goats, buffalo), animal breeds, feed, lactation and other factors. In order to provide consumers with consistent products, most milk in the United States is standardized.
In order to achieve standardization, the milk is treated by centrifugal separator to form degreasing part and cream part. The separation produces a skimmed portion with a fat content of less than 0.01% and a cream portion with a fat content of usually 40%, although the fat content required for the cream portion can be controlled by changing the setting on the separator. The cream portion is then added back to the degreased portion to produce the desired fat content of the product. Common products are whole milk (3.25% fat), 2% and 1% fat milk and skimmed milk (< 0.1% fat).
Most liquid milk is pasteurized for 15 seconds using a high temperature short time (HTST) continuous process of at least 161 ° f (71.6 ° C). These conditions provide fresh milk that meets consumer safety requirements. High temperature treatment, such as ultra pasteurization or aseptic treatment, is used to extend the shelf life of frozen products or allow storage at room temperature, but may bring cooked flavor to milk.
The fat in milk is secreted by cows in small balls of different sizes, ranging from 0.20 to 2.0 µ M. The uneven size of the pellets causes them to float on top of the container or form cream. Heterogeneous milk is sometimes referred to as "cream" milk. Pasteurized milk does not necessarily need to be homogenized. However, homogeneous milk should be pasteurized to inactivate the natural enzymes that degrade fat (lipase), resulting in rancidity, which will lead to peculiar smell in milk and shorten the shelf life.
The purpose of homogenization is to reduce the size of milk fat ball to less than 1.0 µ m and distribute it evenly in milk. Homogenization is a high-pressure process that forces milk at high speed through a small hole to break the ball. The result of homogenization is more and smaller fat balls. The natural milk fat ball is covered with a layer of protein film, which can stabilize the fat phase in the milk water phase (water phase). Although the milk fat globule membrane is destroyed in the homogenization process, it will automatically migrate back to the fat globule after homogenization. The new globules produced in the homogenization process are spontaneously wrapped by the protein in the original milk fat globules in the degreasing stage.
Liquid milk is usually supplemented with vitamin A and vitamin D. The time of adding milk must be indicated on the package label.
Whole milk is considered a good source of vitamin A. Vitamin A is a fat soluble vitamin, which exists in the fat stage of milk.
Special milk beverage
The dairy industry has developed special liquid milk drinks to meet the diversified nutritional needs of consumers. Lactose reduced and lactose free milk and acidophilic milk have been developed for patients with lactose intolerance (dyspepsia). Lactose reduced and lactose free milk is treated with lactase before packaging to separate lactose into its components sugar, glucose and galactose. Acidophilic milk contains Lactobacillus acidophilus, a probiotic lactic acid bacteria beneficial to human health. Lactobacillus acidophilus uses lactose as energy to reduce the content of lactose in milk. They also make lactase, which helps humans digest lactose in the small intestine.
There are special milk drinks customized for specific groups. There are milk drinks with phytosterols added to help raise cholesterol levels, and some are protein and calcium fortified drinks designed for adults. There are carbohydrates reduced and vitamin fortified milk drinks for people to observe their weight. Milk drinks for young athletes are rich in protein and reduce fat. Milk drinks designed for children are calcium fortified, fat reduced and flavored. Flavored milk competes with soft drinks to attract children's attention. It has a variety of flavors, from traditional chocolate and strawberries to their favorite candy bar or ice cream flavored milk.