Microwave processing of foods

Microwave ovens are mainly used for heating and reheating of foods; however, trends show that they are used increasingly also for cooking and defrosting.

Industrial scale microwave processing units have been developed for drying, precooking of meat, pasteurization of ready meals, and tempering of meat and fish. Microwave processing is generally characterized by uniform heating on a macroscopic scale and rapid heating rates, as opposed to conventional processing.

Microwave heating talks place throughout the volume of the product. This volumetric heat delivery leads to a much higher rate of heating than conventional methods, limited by the heat penetration from the heated surface to the bulk of the material.

Microwave processing is used in various industrial application:
*Pasteurization of liquid and viscous in the food industry
*Sterilization of liquid products on food/pharmaceutical sector
*Drying of casings in sausage production
*Heating of minced meat mixtures after the extruder for flashing
*Preheating of viscous products before spray dryers or vacuum dryers
Microwave processing of foods 

Process of microwaving the food

The absorption of microwave by a dielectric material results in the microwaves giving up their energy to the materials with a consequential rise in temperature. Food composition (mainly water content) is a key factor that determines how fast it will heat in a microwave environment.

Cooking food using a microwave oven is accomplished by setting an appropriate amount of time necessary for the waves to penetrate the food and cook it.

The most important advantages of microwave heating is that microwaves are capable of penetrating very deeply into certain materials heating extend within the entire food material, which result in very significant reductions in process heating times for drying, thawing, sterilization and so on.

There are limits to the depth of their penetration. The geometry of the food to be heated is an important consideration; conduction and convection may often take far longer to heat a given mass of food.

Microwaves generate heat due to their interactions with the food materials. The microwave radiation itself is non-ionizing radiation, distinctly different from ionizing radiation such as X-rays and gamma rays.

Heating foods evenly in a microwave oven is difficult at best, particularly with solid foods of different composition.

A major use of microwaves in the food industry is the tempering and thawing of frozen foods, especially meat, fish, butter and fruit.
Process of microwaving the food

Microwave processing

Microwave heating is a kind of radiation heat transfer but it differs in many ways from heat transfer by thermal radiation. Nowadays, the microwave oven is widely used for reheating or prepared foods in the food service sector.

Microwave heating has also found applications in the food industry including tempering of frozen foods, pre-cooking of bacon, pasteurization of packaged foods and final drying of pasta products. It is the first precise and rapid technique that allowed some segments of the food industry to make in process adjustment of the moisture content in food products before final packaging.

Microwaves penetrate deeply into food materials and as they penetrate, the energy they carry is converted to heat, actually by the food material itself, mainly by mechanism of polar and ionic orientation.

Microwaves , like many other radiation, are partly reflected, partly transmitted and partly absorbed. The absorbed fraction generates heat.

Microwave food processor offer a lot of advantages such as less start up time, faster heating, high energy of efficiency, space savings, precise process control, selective heating and foods with high nutritional quality. 

The aim of using microwave processing in preservation in general and pasteurization or sterilization in particular is to deliver a more homogenous heat treatment at a faster rate than conventional heating.
Microwave processing

Microwave Processing – How it works?

Microwave Processing – How it works?
Introduction
Microwave energy, usually generated by a magnetron, occurs as alternating current at either 915 or 2450 megahertz. Both frequencies are authorized by the federal government for use with microwave ovens. Because water molecules are polar (have positive and negative ends), they tend to oscillate as they try top align themselves alternately between the positive and negative charges of the microwave energy.

Function
When the frozen foods are exposed to microwave energy, the liquid water in them (all frozen foods contain some water in the liquid stat) begin to heat due to the friction created by high speed oscillations of the water molecules. Most of the water in frozen foods is in the ice state and is not affected by the microwave energy, until heat generated by liquid water molecules is conducted to the ice, melting it, and thereby producing more liquid water to become involved in the heating process.

History
The first application of microwave energy in industry occurred during the 1070s when cooperative experiments between the Gloucester Laboratory, a USDC facility, and the Raytheon Co. resulted in the introduction of a continuous microwave tunnel in the seafood industry, for thawing or tempering of shrimp and fish blocks. In tempering, the product is not quite thawed yet lends itself to further processing such as cutting or coating with a breading. Microwave Processing – How it works?

Microwave in food processing

Microwave in food processing
Microwave and radio frequency heating refers to the use of electromagnetic waves of certain frequencies to generate heat in a material.

Typically, microwave food processing uses the 2 frequencies of 2450 and 915 MHz. Of these two, the 2450 MHz frequency is used for home ovens, and both are used in industrial heating. It is worthwhile to note that outside of the United States, frequencies of 433.92, 896 and 2375 MHz are also used.

There is not much commercial use of these frequencies for food pasteurization or sterilization, although they are used in baking and other processes in the food industry.

Heating with microwave and radio frequency involves primarily 2 mechanisms-- dielectric and ionic. Water in the food is often the primary component responsible for dielectric heating.

Due to their dipolar nature, water molecules try to follow the electric field associated with electromagnetic radiation as it oscillates at the very high frequencies. Such oscillations of the water molecules produce heat.

The second major mechanism of heating with microwaves and radio frequency is through the oscillatory migration of ions in the food that generates heat under the influence of the oscillating electric field.

Microwave and radio frequency heating for pasteurization and sterilization are preferred to the conventional heating for the primary reason that they are rapid and therefore require less time to come up to the desired process temperature.

This is particularly true for solid and semi-solid foods that depend on the slow thermal diffusion process in conventional heating. They can approach the benefits of high temperature-short time processing whereby bacterial destruction is achieved, but thermal degradation of the desired components is reduced.
Microwave in food processing