President Lou A. Honary WAVEtek Process Technology LLC Professor Emeritus of Innovation, University of Northern Iowa
Important points:
- Traditional heating methods in food processing, such as steam-jacketed containers, are outdated, inefficient and often lead to safety hazards and energy waste, prompting the search for safer alternatives.
- Microwave-based vertical cooking vessels have emerged as a promising alternative, as they can heat products directly without the need for jacketed vessels, scraping mechanisms, or steam boilers.
- This microwave technology offers several benefits, including reduced costs, improved safety, and more efficient energy use, and has the potential to revolutionize food processing both in terms of safety and economy.
Food industry leaders remain alert to technological advances that can impact competitiveness and survival. Advances in technology are often inevitable due to the desire to improve processes, increase safety, and reduce costs. Newer technology often performs better, making it impossible to remain competitive using older technology.
background
One area that is being reevaluated in the food processing industry is heating methods for cooking liquid or semi-liquid products. Current heating methods were invented in the late 19th century.th It was improved in the 20th century.th century. Until the invention of jacketed containers in the 1940s, most food processing heat came from open flames of wood or petroleum products. The invention of jacketed tanks allowed steam and other heat transfer media to be used away from the cooking vessel, providing a safer cooking environment.
In the case of a steam-jacketed container, a heating medium, in this case steam, is directed through the jacket of the container to heat the walls of the container and cook the food inside. Direct flame methods are still used in developing countries and in small-batch confectionery production using propane tanks and small open-top containers. However, since the invention of jacketed containers, steam and heat transfer oil have been used to heat the walls of containers for food cooking and chemical processing.
The use of steam or thermal oils is generally inefficient and dangerous. Unfortunately, instead of considering the large number of fires that have occurred in food processing plants as a reason to look for alternatives, we are assigning blame to negligence without considering the real cause, which is inherently dangerous and outdated technology. It is often inflicted. Heating water to create steam and heating the walls of a container to cook a product requires several forms of energy conversion, each with its own inefficiencies. In addition, hot spots on the walls of jacketed vessels require a surface scrubbing mechanism with a gearbox, drive motor, gear oil, etc. An example of a hot spot in home cooking is the bottom of a pot when cooking on the stove. pot. The bottom of the pan, which is in contact with a heating element or open flame, will be much hotter than the milk, and the fat in the milk will burn if you don’t scrape or stir it. this is possible indirect Heating when the original heat source heats the container rather than the product. All indirect heating diagrams show some form of agitation and scraping due to the presence of hot spots in the cooking vessel. This is done intuitively through evolutionary learning.
If you heat the same cup of milk in the microwave, you’re heating the product directly in the microwave instead of the container, eliminating the need for stirring or scrubbing. The cup remains cool to the touch while the milk is heated to a boil. Direct heating of this product increases safety and has the potential to significantly reduce costs. The challenge was to discover how to apply microwaves in vertical metal tanks to cook large quantities of commercially available food.
Alternative heating methods for commercial cooking
a 2007 Heat transfer oil fire A bio-based lubricant plant in Iowa decided to explore alternative ways to heat its products. Out of all the candidates, including induction, infrared, etc., microwaves were chosen as having the best potential for processing vegetable oils to produce soaps and greases. The process was later patented and production began for heating vegetable oil-based lubricant products. another Heat transfer oil-related fires in 2021the nation’s largest grease and lubricant facility was destroyed at the ChemTool lubricant processing plant in Lockton, Illinois.
Microwave ovens with cubic cooking chambers have been used in homes and food service establishments for over 70 years. The idea of directly heating a product using microwaves in a vertical metal container may seem daunting at first. But in 2010, researchers at the University of Northern Iowa, working with a microwave manufacturer, showed that microwaves could be applied to non-ferromagnetic metals (such as stainless steel, aluminum, and copper) without creating an arc. Since 2010, an Iowa company has used microwaves to process millions of pounds of vegetable oil-based grease this way.
Microwave in vertical heating container for food processing
Most people are accustomed to cooking food in the cubic chamber of a home microwave oven. However, microwave-based vertical metal tanks have been used for more than a decade to heat products. What many people don’t know is that the waves from a microwave generator travel through a small section of waveguide and enter the microwave chamber. The opening of the waveguide is covered with a microwave transparent plate found inside a home microwave oven. The waveguide can be made as long as needed, and the waves can be sent to the galley several feet or yards away.
We know that microwaves can be transmitted through waveguides away from the source. And the fact that the waves can be applied to non-magnetic metals led to the development of microwave-based vertical cooking vessels. The image below shows that by extending a waveguide from inside a conventional microwave oven, waves can be sent into the cylindrical chamber of a crockpot.
With the knowledge that electromagnetic waves from a microwave oven can directly excite the molecules of food inside a stainless steel container, you can imagine the benefits of this heating method.
- This is a direct heating method, so there is no need to heat the walls of the tank to cook the product. This eliminates the need for jacketed containers and means cheaper single-layer tanks can be used for cooking.
- Because the tank walls are not hot, there is no need to scrape the wall surface, and the tank does not require a gearbox or drive motor.
- The steam boiler and its ancillary components are no longer required, further simplifying operation. Instead, a pump under the tank circulates the product during wave application, and a temperature sensor reports the product temperature to the microwave controller.
For purposes of illustration, assume that the operator sets the desired temperature to 90°C (194°F) and the power input to 35kW. The PLC applies 35kW microwaves to the product through the waveguide and the temperature begins to rise and is displayed on the control screen. When the temperature reaches within 1 degree of the set point, in this case 89°C (192.2°F), the PLC reduces the microwave input to near zero. When the temperature drops below 89°C (192.2°F), the wave input increases by several kW and within a few minutes the temperature stabilizes at 90°C (194°F). This state is maintained with minimal energy requirements until operator intervention. If the operator chooses to apply 70kW instead of 35kW, the process is the same, but the time required to reach the required temperature is cut in half. There is an almost direct linear relationship between microwave power input and time to reach the desired temperature.
Current heating methods for processing liquid and semi-liquid foods are outdated and could be reviewed and improved. Microwave ovens have been used for decades to cook products in homes and restaurants. For food industry leaders, wave based cooking Worth exploring. There are many safety and economic advantages that cannot be ignored compared to traditional processing.
