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Introduction
Introduction
The term canning refers to a process which involves heating food stuff in hermetically sealed containers for a specific time at specific temperature to eliminate microbial pathogens that endanger public health and micro-organisms as well as enzymes that deteriorate food during storage. History of canning: Important historical developments in canning are as under:
Manufacturing of cans: Metal cans are mainly used in the national and international trade for canning of fruits and vegetables. Open top sanitary (OTS) cans are made from tin plates which are very thin sheets of steel lightly coated with tin (0.00025 cm thick) on both sides. Tin can is cut into proper sizes with a trimming and slitting machine. The pieces provide body blanks. After notching and slitting, the flat can body is passed through an edging machine where hooks are formed. The can body is then bent into a cylindrical shape and side seam is soldered. These operations are carried in the can manufacturing factory. Now the cans are supplied in the flattened form to the users to lower the packing and transportation costs. The can ends are supplied separately along with the cans. During preparation of can, the first step consists of reforming the cans in can reformer to give them a cylindrical shape. The cans are then flanged by using a flanger, which curls the rims/edges outward at each end. One end of the can is now fixed to the flanged can body by means of a double seaming machine which firstly form the seam and secondly tightens it. The finished cans are now tested for any leaks with the help of a vacuum/air pressure tester. Finally, after the filling of the cans with fruits or vegetables the second lid (end cover) after coding is fixed similarly for airtight sealing of cans. The empty can after placing lid on both the sides can be tested for any leakage by using empty can tester. For testing, the probe of empty can tester is sealed empty can to which air is pumped to about 15-20 psi. Any leakage is judged by immersing can in water. In case of any leakage, the defect in the double seamer needs to be rectified before starting any production. Different sizes of the cans used in canning are showed in Table-7.1. Table7.1: Trade name and sizes of cans used in canning of fruits and vegetables.
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Last modified: Wednesday, 7 March 2012, 5:05 AM