PORTLAND - Scientists at Oregon State University are tuned in to a hot new innovation in food preparation - using radio frequencies to quickly and precisely heat food.
The research team has found that by wedging packages of food between electrodes and tuning radio waves to various frequencies, food molecules vibrate and heat up. By varying frequency of the radio waves and apparent resistance to the electric current, the researchers can tune the flow of energy to precisely the amount needed to heat various ingredients in the food, in a process called impedance match. This allows rapid and uniform heating.
For example, a 25-pound Thanksgiving turkey would normally take about six hours to thaw at room temperature and four to six hours to cook in a traditional oven. With variable radio frequency heating, it is possible to thaw and cook that turkey in less than two hours, according to Qingyue Ling, a development engineer with OSU's Food Innovation Center in Portland and part of the research team.
"By combining variable radio frequency heating with a regular convection oven, the turkey will cook quickly on the inside and be crispy on the outside," said Ling.
Compare this new technology to the cooking breakthrough of a generation ago: the microwave oven. Microwaves are very high frequency and short wavelengths that do not penetrate very deeply. So a microwave oven is an inefficient way to cook a turkey, because it only cooks the surface and depends on heat conduction to cook the inside.
But radio frequency can be 100 times lower, with wavelengths 100 times longer, than microwaves. They penetrate deeply into food, so food cooks faster with less energy.
"Current microwave technology has about 40 to 60 percent energy efficiency," said Ling. "This new radio-heating technology could achieve 70 to 80 percent energy efficiency."
Radio waves also penetrate into wood. There are a few lumber mills in Canada using a version of this process to dry timber, according to Ling. But the volumes of timber, measured in tons, require hours of treatment, whereas the volumes of food, measured in ounces, would require mere seconds or minutes and much more precise temperature control.
"The manual control of temperature used in the Canadian lumber mills was just not quick enough," said Ling. "We needed an automatic system that could sense temperature changes and immediately adjust power rates."
The research team has examined the heating rates of different kinds and amounts of food in the broadband ranging from 10 kilohertz to 100 megahertz. The higher limits of this band begin to overlap with FM radio at about 90 megahertz. In radios, televisions or radar systems, a particular frequency is selected from a band of frequencies. This new technology allows the automatic adjustment across variable frequencies to precisely control the level of heat produced, according to Ling. "Once we identify which frequency we need for each kind of food, we can tune the frequencies more precisely," Ling said.
Characteristics such as density and moisture affect the conductivity of food. Meats, such as that Thanksgiving turkey for example, have more conductivity than, say, small alfalfa sprouts.
But consider foods that contain an assortment of ingredients, such as ready-to eat meals, which could contain meat, corn, soy and spices.
"Some ingredients will heat faster than others," said Ling, "It is a great challenge to uniformly heat food products with different dielectric properties."
"The challenge will be to understand the dynamic interaction of food ingredients, packaging material, and radio frequency field intensity and distribution to insure optimal heating," said John Henry Wells, superintendent of OSU's Food Innovation Center. "Continuing research is needed to optimize this technology for various food processing applications."
Sharing in the most recent patent with Ling and Wells are Yanyun Zhao, a professor and Extension specialist at OSU's Dept. of Food Science and Technology; Ed Kolbe, a mechanical engineer with OSU's Sea Grant Program; Jae Park, a professor at OSU's Seafood Laboratory in Astoria; and Benjamin Flugstad, an electrical engineer and owner of Flugstad Engineering in Port Hadlock, Washington. OSU and Flugstad Engineering jointly own the patents.
Since 1998, the OSU research team has explored ways to use variable radio frequencies as a heating technology to pasteurize and prepare foods as diverse as surimi, alfalfa sprouting seeds and turkey hotdogs. Since then the Food Innovation Center team has obtained a patent for the concept of variable radio frequency heating and for the design apparatus. It now is in the process of receiving patents for 47 different claims of the new technology, and seeking investment funds to develop a prototype of their new technology.