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A separator is a centrifugal device that separates
milk Milk is a white liquid food produced by the mammary glands of lactating mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. ...
into
cream Cream is a dairy product composed of the higher-fat layer skimmed from the top of milk before homogenization. In un-homogenized milk, the fat, which is less dense, eventually rises to the top. In the industrial production of cream, this proces ...
and
skimmed milk Skimmed milk (British English), or skim milk (American English), is made when all the milkfat is removed from whole milk. It tends to contain around 0.1% to 0.3% fat. Background Historically, skimmed milk was used for fattening pigs, and was re ...
. Separation was commonly performed on farms in the past. Most farmers milked a few cows, usually by hand, and separated milk. Some of the skimmed milk was consumed while the rest was used to feed calves and pigs. Enough cream was saved to make
butter Butter is a dairy product made from the fat and protein components of Churning (butter), churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 81% butterfat. It is used at room temperature as a spread (food ...
, and the excess was sold. Today, milk is separated in industrial dairies. Sufficient cream is returned to the skimmed milk before sale.


History

Before the advent of centrifugal separators, separation was performed by letting milk sit in a container until the cream floated to the top and could be skimmed off by hand. A variant container-separator had a nozzle at the bottom which was opened to allow the milk to drain off. A window in the side, near the nozzle at the bottom, allowed the operator to observe when the milk was drained. The centrifugal separator was first manufactured by
Gustaf de Laval Karl Gustaf Patrik de Laval (; 9 May 1845 – 2 February 1913) was a Swedish engineer and inventor who made important contributions to the design of steam turbines and centrifugal separation machinery for dairy. Life Gustaf de Laval was born at ...
, making it possible to separate cream from milk faster and more easily, without having to let the milk sit for a time, and risk it turning sour. Possibly because Gustaf de Laval manufactured the first cream separators, many people credit the invention to de Laval. However, many patents appear before his, all of them labelled as 'improvements'. One of the first specifically for cream separation was patented by W. C. L. Lefeldt and C. G. O. Lentsch. The original centrifugal separators were hand-cranked, as illustrated.


Mechanism

Manual rotation of the separator handle turns a
worm gear A worm drive is a gear train, gear arrangement in which a worm (which is a gear in the form of a Screw thread, screw) meshes with a worm wheel (which is similar in appearance to a spur gear). Its main purpose is to translate the motion of two p ...
mechanism which causes the separator bowl to spin. When the separator is spun, the heavier milk is pulled outward against its walls and the cream, which is lighter, collects in the middle. The cream and milk then flow out separate spouts. After separation, the cream and skimmed milk are mixed together in a certain ratio until the favoured fat content has been set. The ratio is dependent upon the product which is to be produced (low-fat milk, full-fat milk or cream). Some floor model separators were built with a swinging platform attached to the stand. The bucket for collecting the cream was put on the platform, and a much larger bucket was set on the floor to collect the milk. Some floor model separators had two swinging platforms. Smaller versions of separators were called table-top models, for small dairies with only a few cows or goats. Gustaf de Laval's construction made it possible to start the largest separator factory in the world, Alfa Laval AB. The milk separator represented a significant industrial breakthrough in Sweden. Within the first decade of the 1900s, there were over twenty separator manufacturers in
Stockholm Stockholm (; ) is the Capital city, capital and List of urban areas in Sweden by population, most populous city of Sweden, as well as the List of urban areas in the Nordic countries, largest urban area in the Nordic countries. Approximately ...
. Separators in modified form are also used on ships to purify oil, which may have been their original use, because in its original form de Laval proposed the separator for use in his
steam turbine A steam turbine or steam turbine engine is a machine or heat engine that extracts thermal energy from pressurized steam and uses it to do mechanical work utilising a rotating output shaft. Its modern manifestation was invented by Sir Charles Par ...
. De Laval's turbine used mechanically lubricated
journal bearing Plain bearing on a 1906 S-Motor locomotive showing the axle, bearing, oil supply and oiling pad A sliding table with four cylindrical bearings A wheelset from a Great Western Railway (GWR) wagon showing a plain, or journal, bearing end A pl ...
s which were not insulated from the inside of the turbine. When the steam condensed into water it contaminated the oil. To purify the oil a centrifugal separator was used, which was later adapted to the dairy industry. The original design had a manual bowl that required manual cleaning. Most modern separators use a self-ejecting centrifuge bowl that can automatically discharge any sedimentary solids that may be present, thus allowing clean-in-place (CIP). A distinction is made between warm milk skimming and cold milk skimming: * Warm milk skimming separator: At first the raw milk is heated and then skimmed warm. There is a significant difference in density between cream and skimmed milk, because of the higher temperature. * Cold milk skimming separator: Because of the lower energy which is used, the production cost will be reduced. Also at cold temperatures, the growth of microorganisms is significantly reduced. In the US, Mexico, Australia and New Zealand, cold milk skimming is on the rise.


References


Bibliography

*Green, Don W.; Perry, Robert H. ''
Perry's Chemical Engineers' Handbook ''Perry's Chemical Engineers' Handbook'' (also known as ''Perry's Handbook'', ''Perry's'', or ''The Chemical Engineer's Bible'') was first published in 1934 and the most current ninth edition was published in July 2018. It has been a source of c ...
'' (8th Edition). McGraw-Hill Professional, 2007.


External links

{{DEFAULTSORT:Separator (Milk) Dairy farming