Canning and Fish Packaging Technology

Unit 4 - Thermal process for canned foods

4.9.High Temperature Short Time (HTST) Processing
It has been observed that when the temperature of the cold spot reaches sterilization temperature, product near the periphery of the can would have highly over processed especially when the food is processed in a large sized cans. In modern canning methods, retention of sensory and nutritional quality is as important as destruction of microorganisms. To achieve this objective, it is important to minimise the thermal process time by raising the processing temperature. Fish cans which are generally processed to achieve an F_o value of 4 to 6 to achieve commercial sterility which translates to about 60 to 80 minutes at 115^oC for normal sized cans. If the same thermal process is to be achieved at 100^oC, the process time required will be several hours. By the time the fish in the can would have lost all its sensory quality and consumer acceptability. Hence the fish cans are processed at say 115 to 120^oC. If the same principle is extrapolated and processing temperature is raised to say 140 to 150^oC, the processing temperature can be minimised to a few seconds to a few minutes. Such processing methods can be called as High Temperature Short-Time processing. Ball and Olson (1957) have defined HTST process as sterilization by heat for times ranging from a few seconds to 6 minutes. This definition is applicable in case of certain in-can methods of heating achieved in flame sterilizers and some forms of agitation cooker-coolers. However, it is generally applicable to continuous flow sterilization for liquids in which more efficient heat transfer method is used. Milk industry uses the term UHT (Ultra Heat Treated) for continuous sterilization of milk which is nothing but HTST process.