Appts. for sterilising canned foods by induction heating - for quicker and more efficient process than wet heating, without overheating

摘要

Appts. for sterilising foods in cans of 0.15-0.30mm. thick tinned steel comprises a pressurised chamber in which the cans are passed through a series of induction heating coils operating at 8-9 kHz, the power being controlled to limit the temp. of the walls of the cans. Pref. the chamber is pressurised to about 3 bars, to suppress distortion of the cans while the contents are hot. The cans are admitted and discharged at intervals via e.g. rotary vane transfer devices. Pref. the cans travel longitudinally while horizontal and are partly rotated whilst moving between successive induction coils. Pref. the cans discharge via a counter-current water trough which chills the cans from say 127 deg.C to 40 deg.C before they pass out of the chamber and through another counter-current wet trough which chills them to ambient temps. Opt. the water from the latter extracted at about 40 deg.C is used as the input to the enclosed trough. Used esp. for sterilising the contents at 80 deg.C or more without heating above 130 deg.C with an overall thermal efficiency of better than 70%, e.g. about 85%, thus being more efficient than hot water, steam or flame heating. Also quicker, hence reduces the risk of excessive precooking of the contents.