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Quality comes “naturally coloured”

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Food processors are using advanced thermal heating technologies to create natural colour and other qualities in ready-to-eat products

When it comes to ready-to-serve meals, deli products, frozen and even fast-food items, consumers are looking for products that feature authentic colour as well as appealing textures and delicious taste. Food processors are now able to meet those preferences through advances in thermal heat technologies designed for the best yields to a variety of quality standards.

Today, there are four principle methods for developing natural colour 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 colours 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,” says 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 colours they see on chicken prepared on their barbecue grills at home.”

Unitherm has been developing its Flame Grill System for over 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 says.

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

1. 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 colour on top, bottom and all sides of the product. High-temperature air, combined with steam (to create super-heated vapour), 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 colour without the shadowing that you see with radiant heat such as gas infrared,” explains 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 processors to better control the appearance of the finished product. Most recently this impinged air technology is being adapted for use in a spiral oven.

2. Flame
Perhaps one of the oldest thermal heat methods for colouring 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 affect that flame has on any product depends partly on the fat to protein breakdown of the product. The colour result is anything but uniform; however, the taste of a truly flame-grilled product is unmistakable.

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

3. Searing
Using the latest searing technologies, a product can pick up additional colour from the equipment belt at high temperature and/or be marked from searing hot branding irons. Unitherm Food Systems utilizes custom-made branding irons for fancy patterns such as diamonds and crosses. However, it’s not enough to simply make the marks – it’s also the ability to develop colour and texture between the marks. The result is a handcrafted product that looks as if it was chef prepared or cooked on the grill at home.

4. 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 colours 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 colour 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 colour the underside of the product. So if colouring to both sides of the product is important, the product must be uniform in size, shape and weight for it to flip on a transfer conveyor mechanism.

Like gas infrared, electric infrared is a radiant heat. Perhaps the most common example would be a home 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 two-per-cent yield loss. Pasteurizing with this method can also obtain over a 3.0 log reduction in Listeria monocytogenes, according to studies by Dr. Peter Muriana of Oklahoma State University.

Cowherd adds 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 colour while making a safer product for consumers. Industry leaders are using these thermal heat methods to produce high-quality RTE products. The quality comes “naturally coloured,” by impinged air, flame, searing, radiant infrared heat or a combination of these.

For more information contact Unitherm Food Systems at (918) 367-0197 or Visit the website at

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