Electric heating – Metal heating – Of cylinders
Patent
1987-10-27
1989-02-28
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
219 1055A, 219 1055F, 426241, 99451, H05B 678
Patent
active
048087831
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for applying microwave energy in a continuous process for heat stabilization of products and providing treatment conditions that guarantee an end quality close to the quality of fresh or unprocessed products, also for products which are not very resistant to processing and which by experience are difficult to process.
The products of interest primarily are food products, for instance meat, fish, fruit and vegetables and also pharmaceutical compounds as dispersions of nutrition.
It is known to apply microwave energy for heat stabilization in continuous processes.
U.S. Pat. No. 3,809,845 (Stenstrom) represents the state of the art from which the present invention starts.
The contents of another U.S. Pat. No. 3,263,052 (Jeppson) represents the idea of applying mutually different power levels along a conveyor tunnel in a continuous process. In that context the idea is to apply a maximum of energy at a first stage and thereafter reduce the energy supply as the water contents of the product decreases.
Because the primary idea of the present invention is to apply processes for heat stabilization that allow sterilization or pasteurization, the first mentioned patent represents to a substantial extent also the problem in the present context, while the latter patent has less relevance because it relates to drying processes having entirely different prerequisites.
The heat stabilization which is meant has for its purpose to inactivate enzymes and microorganisms without introducing a lower quality, for instance flavour of food stuff. For a long time it has been known that such stabilization should be carried out in a very short time in order to realize the object. Especially for solid or viscous food, microwave are the single means for a sufficiently quick heating. However, generally microwaves heat food stuff or similar products not very uniformly--it is not unusual that a portion of the heated product is given three times higher temperature than another portion. However, this can seldomly be accepted because the quality of the product is reduced quickly when the temperature is too high. When packaging products in plastics there, additionally, is a temperature limit above which the packaging material melts, reacts with the product that is packed or is damaged in some other way. A major step towards a uniform processing is disclosed in said U.S. Pat. No. 3,809,845 where heat stabilization is carried out in a medium surrounding the product and where the medium has a dielectric constant approximately equal to the constant of the product, and where the temperature of the surrounding medium is controlled such that the medium cools the surface of the product in order not to reach a temperature higher than the one desired inside the product.
Some products do require further technique for heat stabilization the product without loss of quality (smell, taste, texture, colour, vitamin contents etc.). One reason for this is that several parameters, individually or together cause a temperature distribution when heating by microwaves.
Such a parameter is inhomogenity of the product. The product may for instance consist of several constituents, for instance potatoes, onion and meat in smaller or larger pieces. Due to the loss factor and the dielectric constant of the microwaves, the several constituents of the product will be given different heating. The distribution and the location inside the product of the several constituents are also important to the heating.
The product may also be a products layered of material types having different loss factors etc. In such a case a layer comprising two materials A and B may give a higher temperature in A when microwave heating at a certain layer orientation, and in B at an other layer orientation. A piece of side flesh may represent a layered product. Another factor the effect of which is temperature distribution is the existence of standing waves in the microwave field inside the product.
Furtheron, tendencies of a too high heating of the edges o
REFERENCES:
patent: 3277580 (1966-10-01), Tooby
patent: 3365562 (1968-01-01), Jeppson
patent: 3809845 (1974-05-01), Stenstrom
patent: 3814889 (1974-06-01), Stenstrom
patent: 4401884 (1983-08-01), Kusunoki et al.
patent: 4525615 (1985-06-01), Wyland
patent: 4553011 (1985-11-01), Nakata et al.
Alfastar AB
Leung Philip H.
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