Package making – Methods – With contents treating
Patent
1997-08-11
1999-01-12
Coan, James F.
Package making
Methods
With contents treating
53440, 53525, 53127, B65B 122
Patent
active
058573127
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to methods and apparatus for thermally processing packaging containers, in particular (but not exclusively) metal cans containing a food product for human or animal consumption.
In a normal canning process the food product is filled into empty cans to an appropriate level, leaving a headspace above the product, the open ends of the cans are hermetically sealed with end closures, and then the cans and their contents are sterilised by means of heat. The heating medium used is normally either steam or hot water at a temperature usually of between 115.degree. C. and 130.degree. C. To achieve this temperature the steam or hot water has to be held at a superatmospheric pressure, and accordingly it is contained in a pressure vessel known as a retort or cooker.
The cans, after filling and closing, are placed in the retort, the retort is closed, and steam or water is introduced. Temperature controllers are usually present on the retort to maintain the heating medium at the desired temperature. While the cans are located in the retort, heat from the heating medium is conducted through the container walls and thence passes into the product.
Insofar as their behaviour during thermal sterilisation is concerned, food products are usually classified into three categories, namely: (1) those that heat largely by convection, (2) those that heat largely by conduction, and (3) those that heat by substantial parts each of conduction and convection. Food products having a very thin consistency heat largely by convection, that is to say, the heating process generates convection currents in the product and these currents disperse the heat throughout the pack; products of this kind fall into category 1. Thick, e.g. relatively viscous or partly particulate, products, heat largely by conduction; for them no significant movement within the container occurs, and so heat can substantially only be transferred by conduction; these products form category 2. The products falling within category 3, which heat by both conduction and convection, form the smallest of the three categories and include those products which either thicken or become substantially more fluid as heating progresses.
Because of the need for complete sterilisation all parts of the food product in a can must reach a sufficient temperature for a long enough time to achieve so-called commercial sterility. With non-acid (pH>4.5) products which heat largely by convection (i.e. category 1 products) this occurs fairly quickly; for example, a cylindrical can of 73 mm diameter and 110 mm length typically takes 15-20 minutes in a retort at 121.degree. C. to heat to sterilisation temperature ("heat-up time") and remain at that temperature for as long as may be necessary to achieve commercial sterility ("dwell time"). The 15-20 minute period, thus made up of the heat-up time and any dwell time of the can in the retort at sterilisation temperature, is commonly referred to as the "process" time, which nomenclature will be used hereafter. The process time is subsequent to any time which may be allowed for the retort itself to heat to sterilisation temperature, hereinafter referred to as the "come-up" time. The come-up time may be considerable, e.g. up to half hour, and some heating of the cans will occur during this time.
The time period formed of the heat-up time of the cans and any come-up time of the retort is significant in the context of the present invention because it represents the time during which the product in the cans is being heated to the sterilisation temperature by heat passing through the can wall. This time period, hereinafter referred to as the "heating" time (of the cans), may be supplemented by any dwell time to form the total time during which the cans are subjected to the heating medium and which accordingly is hereinafter referred to as the "sterilisation", or more generally, "thermal treatment" time.
It will be seen that, using the definitions given above, the sterilisation time is equal to the process tim
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CarnaudMetalbox (Holdings) USA Inc.
Coan James F.
Kim Gene L.
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