Cleaning and grinding of raw materials, preparation for canning
Cleaning of raw materials is one of the most labor-intensive operations in the technology of preserving food products. When cleaning, remove the inedible parts of the raw material - fruit of the fruit, berry sepals, grape crests, seed chambers, the skin of some types of raw materials. Many of these operations are mechanized. There is, for example, a machine for cutting the grains from the corn cobs, cleaning the skins of the fruit and tubers with abrasive materials, etc. However, when cleaning the raw material, manual piles are often used. The same can be said with respect to the subsequent grinding of raw materials, which is often combined with cleaning operations.
The grinding of raw materials is carried out to give it a certain shape, to better use the capacity of the container, to facilitate subsequent processes (for example, roasting, evaporation, pressing). These operations are usually carried out by machine, although sometimes there is the use of manual labor.
Abroad, for example in Germany, produce machines for cleaning and cutting apples, pears and citrus fruits. The machines clean the skin of the fruit, cut it into slices, halves and slices, and also remove the core from apples and pears. These carousel machines. Load the fruit manually. All subsequent operations — cutting the skin, incising the fruit, removing the core with a punch and cutting it into halves or slices — are done automatically.
It is very difficult to carry out mechanized cleaning of peppers from the seed chamber. In many factories, this operation is still carried out manually using special conical tubes. At the Odessa Cannery, prototypes of machines for cleaning peppers were made. Hungarian pepper cleaning and cutting machines for large-fruited peppers are supplied to canneries in our country. Load the fruit into the machine carriers manually. All other operations are mechanized: squeezing the fruit to fix it, drilling the core with rotating knives, cutting the fruit into slices, pushing them through the punch grating and unloading.
It is especially difficult to mechanize the removal of cover leaves from onions.Although the so-called pneumatic pneumatic purges of periodic action work quite successfully, however, before entering the machines, it is necessary to manually cut off the lobes and necks of the bulbs. After the connection of the skin with the bulb is broken, the bulbs enter a grater-type machine, in which they rub against one another and on the side surface and the rotating bottom with notches, while the skin is blown off with a pressure of compressed air under a pressure of 0.6 MPa. A significant number of bulbs, peeled on these machines, have to be cleaned manually.
Grating devices with an abrasive surface and steam treatment under a steam pressure of 0.2–0.3 MPa for 10–30 s are also used to remove the skin from the coed fruits. When leaving the zone of high pressure to the outside as a result of self-evaporation of moisture in the subcutaneous layer, the peel is torn and then easily separated in a washing and cleaning machine under the action of rotating brushes and jets of water.
Some types of fruit and vegetable raw materials are amenable to chemical peeling. For this purpose, processing of fruits in hot solutions of caustic soda is used. When exposed to hot alkali, hydrolysis of protopectin occurs, by which the skin is attached to the surface of the fruit, and soluble pectin is formed. The same happens with the cells of the skin itself.As a result, the peel is separated from the pulp of the fruit and is easily washed off with jets of water during the subsequent showering. For alkaline peaches, a 10% caustic soda solution, heated to 90 ° C, is used in which the peaches are kept for 3-5 minutes. Coeprods are treated with a 2.5-3% solution of caustic soda at a temperature of 80-90 ° C for 3 minutes. After alkaline cleaning, the fruitpans are washed from the skin and alkali in carborundum washing machines with an abrasive surface removed. There are other options for alkaline cleaning of carrots, according to which carrots are treated with a 5-8% solution of caustic soda at a temperature of 95-100 ° C, and then washed in a drum washer with water supplied under a pressure of 0.8-1.0 MPa.
When cleaning the fruit of the stalk can be separated from the fruits and berries on rotating rubber rolls facing each other. The diameter of the rolls and the gap between them must be chosen so as to ensure the seizure and separation of the peduncles without damaging the fetus.
A wide variety of mechanical devices is used to grind raw materials into shapeless pieces or a homogeneous pulp-like mass, which is done, for example, before the subsequent pressing of pulps on presses or when preparing raw materials for evaporation of moisture.Various crushers (two-drum, single and double drum, knife), plunger and disk homogenizers (machines for fine grinding, creating a homogeneous-homogeneous — mass), cleaning machines, etc. are used here. In many of them, fruits and vegetables are not only destruction or crushing, but also the strongest blow to the immobile deck with the help of a working body that develops a large centrifugal force during rotation. As a result of this treatment, the cytoplasmic membranes (membranes) of fruit cells are damaged, the cell permeability irreversibly increases, and the juice yield during subsequent pressing turns out to be quite high. The same can be said with regard to the grinding of tomatoes on cleaning machines before their subsequent boiling in vacuum-dropping machines. Usually, the grinding of tomato pulp 30 is carried out sequentially on two or three wiping machines with gradually decreasing diameter of perforation (s) of sieves. For example, in sieve cleaning machines, the following perforation diameters (in mm) have a sieve: the first —1,2; the second-0.7; the third - 0,5.
The finer the grinding, the larger the surface area of evaporation and, therefore, the greater the rate of evaporation of moisture.Calculations show that the surface area of evaporation when crushing particles of tomato pulp to a diameter of 0.7 mm increases compared to the surface area of particles with a diameter of 1.2 mm by 71%, and when leaving the third sieve - another 42%.
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