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Centrifuge

Centrifuges are used to separate foodstuffs into their constituent parts. The operation of a centrifuge is based on the difference in density between those parts. Centrifugation allows you to clarify milk and reduce the percentage of fat in milk, whey, and cream. Centrifuges are widely used in the making of beverages like juice, coffee, tea, beer, and wine, and in the production of sugar and oil. Centrifuges are also used for washing and drying fruits and vegetables.

Synonyms: centrifuge, milk centrifuge, dairy centrifuge, decanter centrifuge, solid bowl centrifuge, centrifuge for restaurants and cafes, filtering centrifuge, food industry centrifuge, membrane filtration, separators.

 

Centrifuges are used to separate liquid non-homogeneous foodstuffs into their various component parts based on density. They are used to determine the fat content in milk, cream, ice-cream, sour cream and other dairy products, as well as to remove impurities and separate milk into cream and skimmed milk; to divide eggs into their component parts and separate them from the shell; to produce fruit and vegetable juices, wine, beer, and other beverages, various oils and sugar; to prepare raw ingredients for cooking molecular-gastronomy dishes; to extract moisture after salting peanuts and various seeds; to remove excess oil after frying crackers, chips, nuts, and seeds; to prepare caviar and minced meat after washing; and to dry vegetables, fruits, lettuce leaves, and other products after washing (widely used in the restaurant industry).

 

Classification of centrifuges

By separating type

Separating;

Filtering;

Sedimenting or clarifying devices;

Combined systems

By separation factor

Ordinary (less than 3500 RPM),

High-speed (over 3500 RPM);

By how sediment is discharged from the rotor

Manual

Inertial

Blade-type

Pneumatic

Screw-type

Hydraulic

With pulsating/extruding pistons.

By principle of operation

     Periodic

    Semi-continuous (the supply of the mixture runs continuously, while the sediment is discharged periodically)

      Continuous

 

Centrifuges can be distinguished based on their principle of operation:

The separation of a mixture into its component parts can be carried out under the action of gravity in either batch mode or continuous mode: the heavier particles settle to the bottom.

Separation of the suspension can also be done under centrifugal force. There are four designs of centrifuges that operate according to this principle:

Tubular designs consist of a vertically placed cylinder which rotates up to a speed of 15,000–50,000 RPM, inside a fixed body. The components of the mixture therefore form ring-shaped layers, which can then be discharged separately. These devices are used to separate immiscible liquids like sunflower oil and water or to separate solids from liquids.

Disc bowl centrifuges are used in the food industry because they can achieve better separation by forming thinner liquid layers. These devices reach speeds of up to 2000–7000 RPM. Disc bowl centrifuges are used in the making of cream, oil, coffee extracts, and powered drinks.

Solid bowl centrifuges are the easiest to use and are indispensable for extracting small volumes of solids from large volumes of liquids. They consist of a rotating cylindrical bowl into which the product is poured, after which the hard particles settle on the wall of the bowl, while the liquid is concentrated in the upper part of the bowl. These units are used to clarify products by removing solid impurities in the production of liqueurs, oils, juices, beer, and starch.

Centrifuges are vital equipment in the dairy industry. With their help, the fat content of milk, sour cream, ice cream, and cream can be determined using the classic Gerber method. This method is based on destroying the proteins in milk and subsequently dissolving the lipids in isoamyl alcohol.

A separator is a vertical disc centrifuge, which is to separate solid and liquid phases or liquid phases by means of centrifugal force. A disc separator operates by the principle of sedimentation.

Separators, cream separators, and milk purifiers are used directly in dairy production. The last is used to clean milk of any foreign matter, bacteria or spores thereof (bactofuge units); to separate protein from whey, and to dehydrate curds. Cream separates allow you to homogenize milk, divide it into cream and skimmed milk, obtain whey and high-fat cream, prepare raw milk for further processing, and obtain high-quality food products (cheese, curd cheese, sour cream, butter, cream, milk).

According to their design, separators can be open, semi-closed, or closed. In open separators, the processes run without a hermetic seal, i. e. the product is in direct contact with oxygen. In semi-closed separators, the input of the milk is not under pressure and can be either open or closed, while the discharge of the product is closed and under pressure. In closed units, a hermetic seal is ensured.

Various types of equipment:

Decanter centrifuges are continuous filtering devices. These units allow separating foodstuffs based on the difference in the density of the component parts. 

Decanters are used to separate a mixture into its constituent fractions and obtain a product with a low moisture content.

The suspension is loaded via a special tube into a horizontally situated drum. The drum then rotates and gradually accelerates, which ensures that the product is uniformly distributed along the inner wall. Under centrifugal force, the solid particles settle on the walls and move to the conical part of the drum, where the discharge zone is located. The liquid fraction is removed through a special opening.

Decanter centrifuges are used to dry fruits, vegetables, and grain; to produce starches and fruit and vegetable drinks; to clarify wine and beer; to purify cheeses and oils; and to separate pulp/dregs in the production of vegetables bases and beverages.

In the restaurant industry kitchen centrifuges are often used (for washing and drying). They are used for lettuce leaves, spinach, chopped potatoes, berries, and herbs. Today this equipment exists in manual and electric form. The former are intended for home-based businesses or small restaurant kitchens.

Centrifuge applications:

Centrifuge type

Speed, RPM

Product processed

Cream separator

5500–6000

Separation of milk into cream and skimmed milk

Milk purifier

6500–8000

Cleans milk of any of foreign matter

Milk centrifuge

500–1500

For determining the fat content of milk and dairy products

Clarifying separator

 

4400–5000

For separating yeast (beer-brewing, winemaking)

Decanter centrifuge for sedimenting hard particles

2800–4800

Production of starches, juice, beer, cheese, oil, refining sugar, drying grain, and processing fruits and vegetables

 

*approximate specificiations of the most commonly used plants; each model of plant has its own unique characteristics which are described in the passport to the equipment.

The optimal speed for centrifugation is chosen depending on the nature of the input product and your requirements for the finished product. Especially important factors are the viscosity, difference in the phase density, the size of hard particles (if present), as well as the maximum speed that the separable inclusions and phases can withstand without being destroyed. The greater the motor rotation speed, the greater the centrifuge’s separating ability. Accordingly, for coarsely dispersed inputs, speeds up to 9000 RPM are sufficient, and as the particles decrease in size, the rotation speed must be increased up to 25,000–150,000 RPM.

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