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Cutting, slicing, chopping, mincing, pulping, pressing
The objective of cutting, slicing, chopping, mincing and pulping processes is to reduce the size of material either for further processing or to improve the eating quality or suitability of foods for direct consumption.
Field of application
These operations are very widely applied in the food industry. For example, they are used in the processing of meat, fish, cheese, vegetables, fruits, potatoes, and various crops (sugar beet).
Techniques, methods and equipment
A large variety of equipment for cutting, slicing, chopping, mincing and pulping is available,normally adapted to the product to be processed. Equipment can be power- or hand-operated,depending on the size of the operations.
Cutting is used for the size reduction of large to medium sized parts of food material; knives, blades, cleavers or saws are usually used for the cutting. Cutting is an important operation in meat and fish processing. Cutting of meat is used post slaughtering to dress and split carcases, to remove offal and to remove appendages and, where required, excess fat and bones. Carcases are further reduced into retail cuts of joints by the removal of bone, skin and fat. Meat prepared for further processing into ham, bacon, sausage, etc., will be treated initially in a similar manner to fresh meat, and will then be subject to further processing operations. These may include further deboning, derinding, defatting, slicing, comminuting, emulsifying, etc. The cutting equipment used in meat processing includes power operated cleavers, circular or straight saws for splitting carcases, and band saws for the further reduction of the carcases. These are all electrically operated. Special derinding machines are used for separating rind and fat from pork carcases. The cutting of potatoes for the production of french-fries often involves the use of hydro cutters (where the potatoes are conveyed by water at high speed over fixed blades).
In slicing, regular pieces of material are obtained. Slicing equipment consists of rotating or reciprocating blades which cut the food when it passes beneath. Sometimes the material is pressed against the blades by centrifugal force. In other cases, e.g. for slicing meat products, the material is held on a carriage as it travels across the blade. Hard fruits, such as apples, are simultaneously sliced and de-cored as they are forced over stationary knives inside a tube. In the sugar industry sugar beets are cut into thin slices, called “cossettes”. A variant of slicing is dicing (applied to vegetables, fruits and meats), where the food is first sliced and then cut into strips by rotating blades. The strips are passed on to a second set of rotating knives, which operate at right angles to the first set, and cut the strips into cubes.
Many products require the breaking down of raw materials into small particles (comminution). This can be achieved by chopping. Chopping into a coarse pulp is applied to meat, fruits and vegetables. In chopping, the material is placed in a slowly rotating bowl and subjected to a set of blades rotating at high speed. This technique, normally called bowl chopping, is widely used in the production of sausages and similar products. In bowl chopping, the degree of comminution can be varied depending on the knife-speed and cutting time, and in extreme cases the material can be reduced to an emulsion if required.
Mincing is mainly used for the size reduction and homogenisation of meat. A meat grinder is used to mince the meat. This is a lightly constructed screw press with a cutting plate or rotating knives at its outlet. The process is a combination of cutting and extrusion (where the meat is passed through a plate with orifices).
Pulping is mainly used for the size reduction and homogenisation of fruit and vegetables. A moving rough surface ruptures the fruits (vegetables) and squeezes the material through a gap producing an homogenised mass. The most common pulpers are drum pulpers and disc pulpers. Sometimes the pulping process is used for juice extraction.
Pressing as applied directly to harvested grapes (or other raw materials) or marc (after maceration) to extract the liquid part of the raw material. Pressing is used in wine production but also for some other alcoholic beverages.
Different types of presses are used. The main ones are:
Horizontal pneumatic presses
A pneumatic membrane located in the centre of the press is inflated: berries are slowly pressed liberating the must in a tank when the solid parts remain in the press.
Hydraulic compression vertical presses
Grapes are placed in a “cage” which maintains the grapes during the pressing. A horizontal tray presses the grapes vertically. The must flows through the cage and is collected in a tank for further processing. The grapes remain in the cage.
There are also other types of presses: e.g. belt presses, horizontal presses, etc.