Canning and Fish Packaging Technology

Unit 4 - Thermal process for canned foods

4.7.4.Method of determining heat penetration in the can
First the cold spot in the can is determined by fixing the thermocouple in 5-6 cans at various points along the geometrical axis where the cold spot is likely to occur. Then the cans are filled with required quantity of food (as packed in normal processing) with thermo couple tips at different positions. The cans are seamed and heat processed and the temperature is noted. The slowest heating rate indicates the cold spot.
About 6-8 cans of same dimension are then taken, fixed with thermocouple tips at the predetermined cold spot, filled with the product and then the intended process is given by retorting. The retort and can temperature are recorded at the convenient intervals of time ranging from ½ to 1 min for normal products and at 2-5 mins for slow heating products. Temperature and time data are collected as soon as the steam valve of retort is opened and till the completion of process which includes heating and cooling time. The data by the slowest heating thermocouple (and not the average) is taken for further calculations. The data obtained are plotted on a linear graph with temperature on vertical axis and time on the horizontal axis as shown below. This data is used for calculation of heat process the product has received. This is done by one of the two methods,

• The general method of process calculation
• Integrated method of process calculation