Food or edible material: processes – compositions – and products – Direct application of electrical or wave energy to food... – Heating by electromagnetic wave
Patent
1993-02-22
1994-08-02
Yeung, George
Food or edible material: processes, compositions, and products
Direct application of electrical or wave energy to food...
Heating by electromagnetic wave
99470, 99472, 99483, 219686, 219771, 426243, 426244, 426521, A23L 300, H05B 600
Patent
active
053344022
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of heat processing a product, especially but not exclusively foodstuff, and relates particularly but not exclusively to the baking of bread.
The term "heat processing" is intended to cover, inter alia, the cooking of foodstuffs, including for example, the delicate vacuum cooking of meat, fish, vegetables or fruits, the pressure cooking of foodstuffs, and baking of farinaceous products such as bread.
With regard to bread, the time required to bake a loaf can be considerably shortened by baking a loaf's interior by microwaves and rapidly browning the exterior with conventional thermal heating, at temperatures higher than those usual for baking.
2. Discussion of the Prior Art
In industrialized countries it is common to cool bread to 21.degree. C. in order to slice it. Conventional cooling, achieved by conduction of heat from the interior of the loaf to its surface, demands a long period of time. From there heat is conducted to the surrounding air, which heats and leaves the loaf surface by convection currents. Forced air convection is frequently used to accelerate heat removal. The heat transfer is an unsteady state process, one major problem being the low heat conductivity of bread. Increasing the velocity of the surrounding cooling air does not significantly increase the cooling rate of the bread. Using such method a standard 800 gram loaf of white bread generally requires two and a half hours to cool.
Vacuum cooling is a technique which has been used for some years and can be used to cool standard loaves of bread in around three and a half minutes. Both microwave heating and vacuum cooling dehydrate the product to a greater degree than using the normal techniques of conventional thermal heating and cooling thereby increasing the weight loss normally resulting from these normal techniques. This creates an economic disadvantage for low profit margin product sold by weight such, for example, as bread. The advantages of microwave-assisted baking followed by vacuum cooling of bread are extremely high speed, the option of using soft wheat flour only (that cannot usually be used alone to bake bread) and a product with a very greatly reduced microbial contamination free of secondary contamination from cooling air, due to the airless vacuum cooling.
OBJECTS AND SUMMARY OF THE INVENTION
An alternative heat energy source which can be used for baking is radio-frequency heat which, like microwave heating, permits acceleration of the baking process compared with conventional electrical resistance heating.
For convenience the term "dielectric heating" is used herein, where applicable, to include both microwave heating and radio-frequency heating.
The speed of baking by dielectric heating is still limited by the danger of product explosion caused by the rapid creation of internal steam pressure within the product, and it is an object of the present invention to obviate or mitigate this danger.
According to the broadest aspect of the present invention there is provided a method of heat processing a product, comprising the steps of: during at least a portion of said heating processing within said enclosed zone by adding gas and/or subtracting gas from the enclosed zone.
Preferably the product is subjected to microwave heating.
Alternatively the product is subjected to radio frequency heating.
In the cases of roasting meat, coffee, cocoa or the baking of farinaceous products, if there is only steam and no oxygen and/or other gases present in the oven, some of the customary dehydration characteristics and/or thermal disintegration and oxidation reactions will not take place. These reactions can be desirable and essential for the marketability of certain food products, such as the brown crust and the fresh baked aroma of bread. In addition, if a food product is heat treated without oxygen and cooled, consequent oxidation may create undesirable flavors.
The selection of the constitution of supra-atmospheric pressure environment w
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patent: 4812606 (1989-03-01), Eke
patent: 5019412 (1991-05-01), Hattori
patent: 5066503 (1991-11-01), Ruozi
Kansas State University Research Foundation
Yeung George
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