The differences in the types of milk depend on the way they are produced and their fat content. For example, whole milk contains about 4% fat, whole standardized milk, which is widely available for sale is with a minimum fat content of 3.5%, semi skimmed milk contains 1.7% fat, skimmed milk contains about 0.1% fat. In addition, there is a variety with 1% fat. The varieties of milk available are explained below.
Whole Milk
Whole milk is the natural milk with no additions or removals
The variety known as whole standardized milk is produced, having standardized the whole milk to contain a fat content of a minimum of 3.5%.
Whole homogenized milk and whole standardized milk are the same as far as fat and nutrient content are concerned. However, the difference is that the whole standardized milk has undergone a process known as “homogenization” to break up the fat globules in the milk, so that the fat spreads uniformly right through milk to prevent the formation of a creamy layer at the top.
Semi Skimmed Milk
This is the most popular variety in the UK with a fat content of 1.7%, in comparison to whole standardized milk with a minimum of 3.5% fat and skimmed milk with 0.1% fat.
Skimmed Milk
In skimmed milk, almost all fat have been removed, leaving a fat content between 0-0.5% with an average of 0.1%. Calcium content is slightly more compared with whole milk with lower levels of fat soluble vitamins, particularly vitamin A
Organic Milk
This milk is from cows that have been grazed on pasture which are free of chemical fertilizers, pesticides or agrochemicals. This procedure needs a special registration with an approved organic body, subject to regular inspection. The treatment given to milk is identical to regular pasteurized milk.
This is one of the fastest growing markets and has wide variety of flavours with the choice of long expiry, catering to all ages with different tastes. The most popular flavours are chocolate, strawberry and banana. Sophisticated flavours such as peach, mocha or products with Belgian and Swiss chocolate are available to cater mostly to the adult market. Fat content of flavoured milk is around 1%.
Sterilized Milk
Sterilized milk is produced after a rigorous heat treatment to destroy all bacteria in milk. It is available in whole, semi skimmed and skimmed varieties. Under the heat treatment, milk is initially pre-heated to approximately 50oC and homogenized. Thereafter, milk is poured into glass bottles, which are closed with airtight seals.
Evaporated Milk
This is concentrated, sterilized milk with a concentration twice as that of standard milk. The process includes standardizing, heat treatment and evaporation of milk under reduced pressure with a temperatures between 60ºC to 65ºC followed by homogenization to prevent separation under storage and thereafter chilled.
Condensed Milk
The process of concentrating condensed milk is similar to evaporated milk, but with the addition of sugar. Although the product is not sterilized, it is preserved by the high concentration of sugar. Condensed milk could be produced from whole milk, semi skimmed or skimmed milk.
Filtered Milk
Filtration system including microfiltration, ultra filtration and nano filtration is used to produce filtered milk, which prevents acidic bacteria passing through. This system increases the shelf life of the product without affecting the nutritional contents.
Milk is homogenized, heat treated and pre-concentrated before evaporating water and drying to produce milk powder. Although several methods are used including spray drying and roller drying to produce milk powder, spray drying is the most frequently used method where concentrated milk in the form of a mist is fed to a chamber where hot air is in circulation, which helps to evaporate water in the droplets of milk resulting in milk fine powder dropping to the floor of the chamber.
Although skimmed milk powder mixes easily with water, whole milk is not so due to its higher fat content.
Roller drying is an old process which spreads the concentrated milk onto heated rollers to help quick evaporation of water, leaving a thin film of powder on the rollers which are scraped off. This powder gives a cooked flavour and tends to form lumps when mixed with water.
Whole milk powder has almost all the nutrients what is there in whole milk in a concentrated form without vitamin C, thiamin and vitamin B12. Skimmed milk powder is almost devoid of any fat and as a result, there are no fat soluble vitamins. Nevertheless protein, calcium and riboflavin content remain unchanged.
Skimmed milk powders have a shelf life of about one year, if stored properly. Once they are reconstituted, they must be treated as fresh milk.