Retorting microwave

The market for plastic cookware that can be used in the fi-eezer and microwave is set for a big expansion. Most cookware is made up of fiberglass reinforced thermoset resins. High-barrier multilayer containers that have gained popularity in the market are heat retortable, microwaveable, and provide a shelf life of up to two years without refrigeration for a variety of convenience foods. Liquid crystal polymers have also been used to make cookware as they are transparent to microwave, offer high heat resistance, and give an excellent finish. 

Attempts have been made to perform thermal retorting ia a gas barrier flexible pouch or tray. The retort pouch, under development for many years, has a higher surface-to-volume ratio than a can and employs a heat seal rather than a mechanical closure. Similarly, plastic retort trays have higher surface-to-volume ratios and are usually heat seal closed. Plastic cans iatended for microwave reheating are composed of bodies fabricated from multilayer plastic including a high oxygen barrier material, plus double-seam aluminum closures. 

Shale oil and a fuel gas have been produced by microwaveheating oil shale in a standard microwave oven in conjunction with experimentation to develop an in situ microwave retorting process. Various grades of oil shale have been subjected to high microwave fields. The derived oil has been submitted to various physical and chemical testing methods, and the chemical composition of the evolved gas has been evaluated. The specific gravity pour point yields of oil, water, gas, and losses and spent shale are compared with parallel data obtained with the Fischer assay procedure. Important differences in oil flow properties and gas composition are discussed in view of microwave interactive theory. 

It is well known that important differences do occur with different methods of thermal retorting, and microwave interactive theory indicates even greater differences may be possible. We examined the products of this novel retorting system by using product quality as feedback control to gain some insight into the basic microwave interaction with fuel precursors. 

Table I. Initial Results on Retorting Oil Shale by Microwave Power...

Averaged overall properties of the crude oil obtained by microwave interaction are summarized in Table V. Although these published figures are not the best for some of the processes listed (2), they are presented for an approximate comparison. From these data, microwave-produced oil is shown to be a suitable liquid fuel precursor although differing from that produced from a variety of thermal processes. The recoveries from this prototype, multimode, cavity-retorting system are promising. 

The initial design for retort pouches, and the one still used by the military, was a multilayer lamination containing an outside layer of polyester, a layer of aluminum foil, and an inside layer of polypropylene. The polyester provides strength and puncture resistance, the aluminum provides barrier, and the polypropylene provides the sealant and product contact layer. A significant disadvantage of this structure is that the food cannot be heated within the pouch by microwaving. 

Retortable plastics. Retortable plastics packs are directed at two markets competition with tinplate or aluminium cans and glass jars in parts of the shelf-stable foods market where the foods can be reheated in the bowl or tray and replacement of chilled or frozen foods in the ready-to-eat (single serve) mode in a shelf-stable format. The aim is to provide food subjected to a somewhat shorter heat process than with cans, due to the flatter geometry of the packs and provision for microwave reheating for convenience in the home, institution or vending machine. 

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