Separation of fat or cream from milk

Most milk plants separate milk for standardization or the obtain cream for bottling purpose and skim milk for butter milk and cottage cheese.

A layer of cream will form on the top of fresh milk, as it comes from cow, if it is allowed to stand for twenty or thirty minutes. This known as gravity creaming and it was very important prior to the invention of the cream separator. For many years it was customary to heat milk to 85 to 95 °F separation, because at this temperature the difference in density between the fat and skim milk is greatest and results in the most efficient separation of fat from skim milk.

Cream is separated from milk in a cream separator. Cream separator is a heavy metal bowl spinning at a very high speed which sediments the skim milk phase of incoming milk toward the wall of the bowl and displaces the cream inward along the centre of the bowl.

The cream and skim milk can then be recombined in desired ratios to obtain low-fat, light and whole milk with 1%, 2% and 3.25% fat respectively. This standardization usually is performed in a continuous manner.
Separation of fat or cream from milk

Skimmed milk

Milk is highly nutritious food that provides nearly all the substances essential for good health in people of all ages. About 4% of whole milk is fat. The fat that separates from milk is cream. Milk which has had the fat or cream removed is called skimmed milk.

Skimmed milk, which may contain 0.5% fat or less, has been a popular beverage for many years. Skimmed milk is as nutritious as whole milk, but contains much less fat and cholesterol than whole milk.

The fat-soluble vitamins – A, D, E and K - are removed with the fat when milk is skimmed. Consequently, they are present in only trace amounts in skimmed milk and in reduced amounts in semi-skimmed milk. Usually this milk is fortified with vitamins A and D.
Skimmed milk

Skim of low-fat milk processing

Dry milk was referred to as milk powder until the mid 1960s, when the designation was changed by the American Dry Milk Institute to dry milk in the United States.

Large quantities of skim of low fat milk are dried. This may be done by spraying atomized droplets of milk into chamber through which heated air is circulated (spray drying).

The atomizers used in this process include mainly rotary and pressure types. The final articles size of the dried powder produced by utilizing a rotary atomizer and the basic plant is greater than 1000 microns.

The milk also may dry by allowing it to flow over the surface of two heated metal drum that rotate toward each other.

A thin layer or film of product is dried over an internally steam-heated drum with steam pressure up to 620 kPa and 149 °C. Approximately 1.2 – 1.3 kg steam are required per kilogram of water evaporated.

The dried milk then is scraped from the drum surface, as they rotate, by metal scraper.

The operating variables for a drum dryer include condensation of incoming product in an elevator, temperature of incoming product, steam pressure in drum, speed of drum, and height of product over drum.

Dried milk (usually the spray dried type that contains about 5% of moisture) may be re-humidified to slightly higher moisture content after drying.

It has poor dissolving properties and where sold for domestic use is subjected to further instantisation, which agglomerates granules and leads to a faster dissolution time.
Skim of low-fat milk processing 

Skimmed milk

Skimmed milk consists of milk from which most of the fat has been removed but which contains all of the protein.

Skimmed milk has very little fat but contains almost all of the protein, lactose (milk sugar), minerals and water-soluble vitamin to be found in standard milk. The protein has a high biological value and is very digestible. Skimmed milk is a good source of B vitamin, but the fat soluble vitamins (and D) have been removed.

Skimmed milk is available as a powder or in ready to use liquid form.

Skimmed milk concentrate is manufactured for use as a food ingredient in its own right, finding application in many sectors of the food industry.

Skimmed concentrate produced for use as an ingredient has relatively low solids content, usually between 35-40% total solids.

Skimmed powder is by far the most important of all the milk powders produced. Skimmed milk can be dried in any of the various types of spray drier available, but for reasons of economy and quality, it is usually chamber with a conical base.

Before drying, the skimmed milk is first evaporated to a concentration of about 50% total solid.
Skimmed milk