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From: Food Quality & Safety magazine, December/January 2008

Infrared Technology Chips Away at Waste

Infrared temperature measurement lets tortilla chip maker run a more efficient operation

by Wes Lowery and Frank Schneider

It is no surprise that flour and corn food products, including tortilla chips, are so popular with consumers: They’re fresh and flavorful when served at your favorite restaurant or purchased from your local market. The high quality of today’s tortilla products is made possible by modern production machinery and processing techniques. New equipment enables manufacturers to improve the taste, appearance, and consistency of corn and flour tortillas, tortilla chips, flat breads, pizzas, and other similar products. Some equipment uses the latest advancements in infrared (IR) temperature measurement technology to optimize the performance of gas-fired ovens used in flour and corn food production operations.

Let Them Eat Cake

In the growing U.S. snack food market, tortilla chips may soon overtake potato chips in total sales. According to the Snack Food Association (Alexandria, Va.), Americans consume 1.54 billion pounds of potato chips annually; tortilla chips are close behind at 1.43 billion pounds.

The Spanish first coined the term tortilla (from the Spanish word “torta,” meaning cake) in Mexico, where it was used to describe flat corn and flour cakes. All tortillas were originally made from the pulp of ground corn. Later, when wheat was brought to the New World, white flour tortillas became prevalent.

After tortilla products were first introduced in the southwestern United States, the popularity of the new food item spread rapidly. Today, tortilla chips can come in many different sizes and shapes, such as triangles, rounds, and rectangular strips.

The basic methods involved in tortilla and tortilla chip production have changed little since ancient times. Traditional tortilla preparation involves cooking and steeping (soaking) the corn, pouring off the cooking liquor, and washing the nixtamal (the end product of the cooking, steeping, and washing/draining process). The nixtamal is then dried and ground into corn flour, or masa.

But some things have changed. Today, automated tortilla and tortilla chip factories use gas-fired ovens to bake the formed masa. Tortilla chips are baked at temperatures ranging from 500 to 554°F (260-290°C), with baking time varying from 35 to 50 seconds. Baking enhances the alkaline flavor of the chips and reduces moisture and oil absorption during frying. The tortilla chips are cooled to produce a more uniform consistency and to reduce blistering.

The next step involves frying the chips in oil at temperatures ranging from 338 to 374°F (170-190°C). Salt and seasonings are applied immediately after frying, while the chips are still hot. The chips are then conveyed into an inclined rotating cylinder, where a liquid seasoning mix is sprayed on them. Upon cooling, the oil crystallizes, forming the seasoning coat.

Ensuring a Quality Chip

As in other food production settings, the quality control aspects of tortilla and tortilla chip production are essential. Among the parameters controlled during the production process are the cooking, quenching, steeping, baking, and frying times and temperatures; the moisture content of the corn, nixtamal, masa, and the end product; and the operating condition of the equipment (including the cooker, oven, fryer, and cooling rack).

For Casa Herrera (Pomona, Calif.), a leading supplier of production machinery for flour and corn food products, temperature control is key to ensuring a consistent, high-quality manufacturing operation. Casa Herrera is behind many of the current gas-fired oven designs used for tortilla production. The company’s product line ranges from individual production machines to entire automated assembly lines, including ovens, flour presses, “sheeters,” and other specialty equipment.

Tortilla chip factories utilizing gas-fired ovens are concerned about “toast points,” small brown burn spots on the tips of the tortilla chip that occur during the production process. Maintaining the desired toast point hinges on the proper measurement and control of temperatures in oven heating zones.

In a typical gas-fired oven, a series of conveyer belts are used to carry tortilla chips during baking. Variable-rate burners are situated between the belts to sear the chips on each side. The product bakes on the top belt and is then flipped over onto the middle belt going in the opposite direction. The chips are flipped over one more time onto the bottom belt to complete the baking process. The chips exit the oven in the same direction they entered (Figure 1, p. 44).

During the preparation of corn tortilla chips, fast heating of both product surfaces is essential for retaining a suitable moisture level inside the chips. The baking process depends on precise control of belt temperature inside the oven; the tortilla chips must be seared in a way that bakes in flavor without leaving visible burn marks.

Accurate Temperature Readings Are Key

In the past, most tortilla equipment manufacturers utilized thermocouples to indicate the ambient air temperature inside their ovens. Thermocouples consist of two strips or wires of different metals, joined at one end. Changes in temperature at their junction induce a change in electromotive force (emf) measurable across the leads. As temperature rises, the thermocouple emf rises. Sometimes an array of thermocouples, aptly called a thermopile, is used.

A thermocouple is one type of contact temperature sensor and is the cheapest and easiest to use. Nevertheless, thermocouples are incapable of measuring direct surface temperatures. Their readings may not accurately reflect oven conditions during process heating. This drawback limits the ability of tortilla and tortilla chip factories to optimize baking cycles during production runs.

Increasingly, manufacturers of process heating equipment are choosing IR temperature measurement technology over traditional thermocouples. IR thermometers are useful for measuring temperature under circumstances in which thermocouples or other probe-type sensors, for a variety of reasons, cannot be utilized or do not produce accurate data. A unique characteristic of IR thermometers is their ability to determine the temperature of an object without making physical contact with it.

The principle of IR and its non-contact nature offers many advantages for process ovens. IR temperature monitoring eliminates the risk of contaminating the product, a feature which is extremely important in the food processing industry. Furthermore, IR sensors save time and money in situations where another type of contact sensor would require that machines be shut down.

IR instruments measure temperature according to Planck’s Law of blackbody radiation, which states that every object emits radiant energy and that the intensity of this radiation is a function of the object’s temperature. The sensor finds an object’s temperature simply by measuring the intensity of radiation.

An IR thermometer can be compared to the human eye. The lens of the eye represents the optics through which the radiation (flow of photons) from the object reaches the photosensitive layer (retina) via the atmosphere. This is converted into a signal that is sent to the brain after being compensated for ambient temperature variation (Figure 2, p. 45).

Every form of matter with a temperature above absolute zero emits infrared radiation according to its temperature. The internal mechanical movement of molecules causes this phenomenon, known as characteristic radiation. The intensity of this movement depends on the temperature of the object. Because the molecule movement represents charge displacement, electromagnetic radiation (photon particles) is emitted. These photons move at the speed of light and behave according to the known optical principles. They can be deflected, focused with a lens, or reflected from reflective surfaces.

Sensor Advancements

For its current oven designs, Casa Herrera employs the Raytek Thermalert TX infrared temperature sensor (Raytek Corp.; Santa Cruz, Calif.; Figure 3, right). This device combines non-contact temperature measurement with industry standard two-wire technology. The sensor provides digital communications and 4-20 mA output, allowing remote configuration and monitoring. If needed, multiple sensors can be installed on a single multi-drop network.

The smart TX sensor used in this application has a temperature measurement range of 0 to 1000°F (-18°C to 500°C), with an optical resolution of 33:1. It provides remotely adjustable temperature and output sub-ranges, adjustable emissivity, ambient temperature check, and a user-defined alarm output. Averaging and advanced peak/valley hold algorithms enable accurate measurement and control of process heating.

Using the IR system software, oven operators can set temperature and output ranges, emissivity, and alarm points and can then monitor temperature data from multiple sensors. Production data can be archived or exported to other applications for analysis and process documentation.

Casa Herrera’s Odyssey oven, which features a fuel-efficient combustion system for flour and corn tortillas and tortilla chips, employs a total of three IR thermometers—one for each product conveyor belt. Non-contact devices with extended optical resolution, the TX thermometers can be mounted outside the oven’s heating zone (Figure 4, p. 46).

The IR devices provide a precise measurement of belt surface temperature as tortilla chips go through the oven. Data is fed to a temperature controller, which, in turn, governs an actuator in open or closed position and maintains a constant temperature on the belts under all load conditions. This technique improves control of temperature set-point limits in the baking process and, ultimately, ensures a better final product.

Improved Products and Consistency

Thanks to advanced IR temperature measurement technology, factories producing flour and corn food products can monitor temperature levels in their production processes with increased efficiency. This results in higher quality products of greater consistency.

Improved methods for temperature detection and control also enable tortilla and tortilla chip manufacturers to reduce scrap—and increase their product yields. Prior to the use of IR thermometers, ovens had to remain idle during reheating after a production shutdown. Otherwise, a certain amount of product on the conveyor belts would burn during the restart period.

Now, with precise, direct conveyor belt temperature measurements supplied by IR sensors, process-heating cycles can restart immediately without any loss of product. Manufacturers have seen this technology improve their bottom line.

The traditional techniques for tortilla and tortilla chip production are optimized through the use of IR temperature measurement. Manufacturers of process ovens have switched from older thermocouple technology to modern infrared thermometers, and product quality and consistency have never been better.

Lowery is technical services manager for Casa Herrera, Inc. Schneider is worldwide product manager for all Raytek point sensor products; reach him at (831) 458-1175, ext. 225 or frank.schneider@raytek.com.

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