Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Microwave energy
Reexamination Certificate
1999-11-29
2001-05-22
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Microwave energy
C034S264000, C034S265000, C034S275000, C034S418000, C034S203000
Reexamination Certificate
active
06233841
ABSTRACT:
The present invention is generally directed to the dehydration of food products and in particular, is directed to dehydration plants for this purpose.
Dehydration is a well known method of preserving food products. During the dehydration process the water content of the food product being dehydrated is reduced to make the food product unsuited to the growth of spoilage organisms. It has been found from extensive scientific tests upon different food preservation methods that the nutritional contents of food is least affected by appropriate dehydration. Furthermore, the economics of transporting food products such as manufactured meats can be greatly improved by dehydrating these foods to a dried form at their point of production and on shipping. Under these circumstances, savings on both weight and bulk of up to 70 percent can be achieved together with dispensing with the need for refrigeration, an aspect important to developing countries.
Two methods are currently used for drying food products;
a) heat applications to remove water; and
b) freeze drying procedures.
Solar dehydration is not suited to mass production in Western countries due to high labour requirements and poor hygiene control. Oven drying is therefore at present the most widely used method of commercial dehydration and involves exposure of the food product to dry, heated air. Many food products are now dried by placing them into a chamber where heat is applied by either gas or electricity. Water in the food product is heated until “boiled off to become dry. This normally occurs at high temperatures and is sensitive to both atmospheric humidity plus ambient temperature. Pre-cooking before dehydration results in a more acceptable product than dehydrating from the raw state.
Freeze drying, also known as “lyophilisation” involves first freezing the food product then directly sublimating ice from frozen to the gaseous state by severe decompression. Flavour changes are minimal, product shrinkage is negligible and the dried material is porous and readily re-hydrated.
Disadvantages of the established dehydration plants includes the high capital costs in setting up and running of such plants, particularly in the case of freeze drying plants. Furthermore, the food product and its taste can be degraded by excessive heating. In particular, freezing can result in changes in the food texture which results in a textural defect known as “woodiness”.
Furthermore, dehydration plants using either oven drying or freeze drying generally involve batch processing of the food product. Also, environmental waste problems are created by the use of such dehydration plants.
It is therefore an object of the present invention to provide a dehydration plant which overcomes at least one of the above noted problems.
With this in mind, and according to one aspect of the invention herewith, there is provided a dehydration plant for dehydrating food products including:
(a) a microwave kiln;
(b) conveyor means for conveying food products through the kiln;
(c) circulation means for circulating air through the kiln;
(d) refrigerated dehumidification means for dehumidifying the air to be circulated through the kiln; and
(e) heating means for heating the air to be circulated through the kiln; such that food products conveyed through the kiln are exposed to both microwave emissions and the flow of dehumidified heated air to thereby dehydrate the food products.
The dehydration plant may be accommodated within an enclosure, which may be transportable as a fully self contained unit to thereby facilitate installation of this dehydration plant. The enclosure may for example be in the form of a standardised industrial freight container.
The microwave kiln may include a kiln tunnel through which food products can be conveyed. The kiln tunnel includes microwave emission means for exposing the food products conveyed through the kiln tunnel with microwaves. The microwave emission means may include a plurality of microwave emitter horns spaced in the elongate direction of the kiln tunnel. Microwave reflection means may be provided for each emitter horn.
The conveyor means for conveying food products through the kiln tunnel may include at least one conveyor belt arrangement extending through the kiln tunnel. The conveyor belt arrangement may preferably include a plurality of conveyor segments. Each conveyor segment may have a forward upstream end and a rear downstream end and may be located on an incline such that the rear end of the conveyor segment is higher than the forward end thereof. The conveyor segments may be positioned such that the trailing rear end of one conveyor segment may be located above the front end of the next adjacent conveyor segment. This overlapping arrangement of the conveyor segments allows for the food products carried by the conveyor means to “cascade” from one conveyor segment to the next adjacent conveyor segment. The conveyor means may also include an intake conveyor provided upstream of the conveyor segments for carrying food product into the microwave kiln tunnel, and a discharge conveyor provided downstream of the conveyor segments for carrying food product out of the microwave kiln. Both the intake and discharge conveyors may be extendible from and retractable into the plant enclosure.
Each conveyor segment may include a conveyor belt supported on and moveable about a front and rear conveyor drum. The conveyor belt may be formed of a plurality of chain links. The chain links may be connected by tie rods and positioned to thereby provide openings through the conveyor belt. As the conveyor belt is exposed to microwaves, each chain link may for example be made of a bipolar or low loss dielectric plastic and the tie rods may be formed from nylon or similar dielectric material. Each chain link may include a lateral spike for effecting increased turbulence about the conveyor belt as well as helping to hold the food product on the conveyor belt. Alternatively, the conveyor belt may vary from coarse chain mesh through to a fine gauge chain mail with ultrafine gauge comprising polypropylene woven belt mesh, accordingly best suited to differing produce.
The drive drums of each conveyor segment may be lined with metal such as stainless steel for reflecting microwaves. A microwave reflector dish may be located between the front and rear drive drums of each conveyor segment to provide the lower reflector portion of a microwave oven compartment of the microwave emission means. A corresponding upper reflector dish may be located above and at least substantially parallel to the lower reflector dish of each conveyor segment. Both the upper and lower reflector dishes may be made of metal such as stainless steel. A plastic cover may be provided over the lower reflector dish to prevent food product falling into the dish. The cover may include along the forward upstream edge thereof an extendable edge lip which may act as an air deflector. The edge lip deflector may further include a row of nylon prongs for underside engaging and effecting ratchet agitation of the conveyor chain-mesh progression. Other conveyor agitation mechanisms are also envisaged. A plastic cover may also be provided over the upper reflector dish. The lower and upper plastic covers therefore provide a narrow processing passage through which the heated dehumidified air can pass therethrough together with the conveyed and agitated food product.
At least one said microwave emitter means may be located within each upper reflector dish. At least one microwave deflector fan may also be located within each upper reflector dish. Each deflector fan may include metal deflector paddles which act as mode stirrers to more evenly disperse the microwave emissions from the emitter horn and reflected from the upper and lower reflector dishes.
Side plates may be provided on either side of each conveyor segment. Each side plate may be coupled to the lower reflector dish such that the conveyor segment can provide an assembly for supporting the conveyor drums and belt to thereby provide a unit which m
Australian Rural Dehydration Enterprise Pty. Ltd.
Burns Doane Swecker & Mathis L.L.P.
Gravini Stephen
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