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From: Food Quality & Safety magazine, February/March 2012

Thermal Heating Technologies Create Natural Color in Ready-to-Eat Products

by Ed Sullivan

When it comes to ready-to-serve meals, deli products, frozen, and even fast food items, consumers are looking for products that feature authentic color as well as appealing textures and delicious taste. Now food processors can give customers what they want using advances in thermal heat technologies.

There are four principle methods for developing natural color with thermal heat: impinged air, flame, sear, and radiant infrared heat. With advancements in modern cooking technologies and natural browning agents, a whole range of authentic colors and surface effects can be achieved faster, more efficiently, and more consistently. This enables processors to create foods with subtle differences in appearance, ranging from products traditionally made at home to those prepared by top chefs.

“Regarding quality RTE (ready-to-eat) products, consumers are placing a higher demand on our industry to develop products that appear to be naturally processed,” said Adam Cowherd, vice president of International Sales at Unitherm Food Systems in Bristow, Okla. “In the case of a grill-marked chicken breast, customers are beginning to ‘read between the lines’ of the traditional bar marks and want to see the same naturally occurring flamed highlights and colors they see on chicken prepared on their barbecue grills at home.”

Unitherm has been developing its Flame Grill System for more than 15 years and offers current models with multiple independently controlled ribbon burners, adjustable bar markers, and relative temperature controls. “Everything characteristic of the flame can be adjusted, from the angle to the length,” Cowherd said.

Advanced flame grills are just one example of how equipment suppliers are using more flexible technology to provide a wider range of finished color and texture. Here is a breakdown of the four most common thermal heat technologies used by leading food companies:

Impinged air: With this thermal technique, high-velocity air is forced directly to the product surface. For product surfaces that are less uniform, this technology can be used to develop uniform color on the top, the bottom, and all sides of the product. High-temperature air, combined with steam to create super-heated vapor, can be used in combination with impinged air to speed up the browning process. This thermal heat method is appropriate for meat, poultry, pasta dishes, and a variety of baked foods, like pastries and pizza bases.

“The effect we see from products that are processed with impinged air is more uniform color without the shadowing that you see with radiant heat such as gas infrared,” explained Cowherd.

New impinging oven designs, such as Unitherm’s versatile RapidFlow Oven, offer touchscreen controls that allow processors to alter multiple parameters, including the velocity of the impinged air, temperature, and humidity control. If they choose, these parameters may be used to create new recipes that are stored for future use. Such features enable a processor to better control the appearance of the finished product.

Most recently, impinged air technology is being adapted for use in a spiral oven. Unitherm unveiled its impinging spiral oven at the Food Processing Suppliers Association show, held in Chicago Nov. 1-4.

Flame: Perhaps one of the oldest thermal heat methods for coloring products is flame. Currently, the term “flame grilled” is used to market everything from chicken wings to fire-roasted tomatoes for spaghetti sauce. Today’s flame grill machines can be used for an array of products, ranging from burgers to veggies, chicken, and fish.

The effects flame has on any product depend partly on the fat-to-protein breakdown of the product. The color result is anything but uniform, and the taste of a flame-grilled product is unmistakable.

Cowherd added that the combination of flame and surface marking create a much more authentic appearance and taste. Additionally, the flame grill can sear in moisture, which results in higher yield and significantly improves the “re-heated” quality product.

Searing: Using the latest searing technologies, a product can pick up additional color from the equipment belt at high temperature and/or be marked with searing hot branding irons. Unitherm Food Systems utilizes custom-made branding irons for fancy patterns such as diamonds and crosses. Simply making the marks is not enough, however; the ability to develop color and texture between the marks is what sets the new technology apart. The result is a handcrafted product that looks as though it were prepared by a chef or cooked on the grill at home.

Infrared: Infrared is one of the hottest thermal heat technologies in the industry and is usually either gas or electric heated. Gas infrared units commonly consist of a flat-surface burner head, which allows processors to develop colors with highlights, achieving a high-note/low-note appearance, where the higher points of the food surface brown more quickly because of their proximity to the infrared head. This fixed-head technology provides continuous in-line cooking and produces the golden-brown color and unmatched yields required by a major fast food chain in the preparation of foods such as breakfast sausage patties. One downside to this technology is that it cannot be used to color the underside of the product. If coloring both sides of the product is important, the product must be uniform in size, shape, and weight so it will flip on a transfer conveyor mechanism.

Like gas infrared, electric infrared is a radiant heat. Perhaps the most common example is your toaster. Advances in electric infrared systems have resulted in higher temperature black-bar emitters that allow rapid browning on all surfaces of the product. Used in combination with liquid smoke, a fully cooked deli product, for example, can be post-process pasteurized and smoked in 60 seconds with less than 2% yield loss. Cooking with this method can also obtain a greater than 3.0 log reduction in Listeria monocytogenes, according to studies conducted by Dr. Peter Muriana of Oklahoma State University.

Cowherd added that the majority of smoked deli meat manufacturers in the U.S. are using electric infrared technology. By smoking and browning in-line with Unitherm’s Infrared Pasteurizer, processors can control color and also make a safer product for consumers.


Ed Sullivan is a Hermosa Beach, Calif.-based writer. He has researched and written about advanced technologies, health care, finance, and real estate for more than 25 years.



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