Keeping ovens consistent
May 2, 2016
by Dan Malovany
Maintaining the heat balance in a tunnel oven requires critical control of the temperature, both linearly — or length of the chamber — and laterally or throughout the width of an oven zone, according to Darren Jackson, COO and vice-president of sales and marketing, The Henry Group.
Many times, he added, bakers put too much emphasis on technological advances, especially when comes to baking bread, rolls, croissants and other similar panned baked goods. Rather, it takes old-fashioned baker know-how and sound mechanical ingenuity to ensure a consistent bake over the life of an oven — which often can be anywhere from 20 to 30 years or more. A superior oven provides the basis for quality control.
“When it comes to ovens, it’s all about heat, air movement and other factors that have been around a long time,” Mr. Jackson said. “You can have the latest whiz-bang PLC program, but if you don’t move air around, you won’t get your heat properly balanced throughout an oven. That’s typically done mechanically. Bakers need to remember to focus on the basics and what makes a good oven. Like they say, buying a great car with cheap tires doesn’t do you a lot of good.”
Like cars, ovens come in all styles. At the International Baking Industry Exposition (IBIE), which runs Oct. 8-11 in Las Vegas, bakers and snack producers will also see hybrid ovens that mix and match various technologies custom-tailored to achieve the desired finished product quality, according to Rick Parrish, director of sales and marketing, Franz Haas Machinery of America. Some hybrid or convection ovens can typically reduce bake times up to 15% from traditional direct-fired ovens.
Heat is transmitted three ways. “Conduction gives the fastest temperature difference, but the second fastest method is convection where the energy is being transferred to the products efficiently, and radiation represents a much slower method of transferring energy to the products,” he noted. The choice of transmission method determines baking action, and ovens can be designed to use multiple methods.
Ovens maintain consistent individual zone conditions by adjusting the distribution of top/bottom heat, controlling humidity in the baking chamber or varying the amount of convection and radiant heat. “Additionally, a humidity control system can be built into each individual zone,” Mr. Parrish said. “The system contributes to a residual humidity accurately balanced in the product. In this way, it is possible to optimize the baking process for each individual product and save these parameters within the PLC recipe management program for automated control for each different product.”
Those controls may have an HMI interface with stored recipes that automatically make adjustments between product changeovers, said Jeff McLean, sales manager, North America, Spooner Vicars Bakery Systems. Moreover, using a combination of convection with direct gas-fired, for instance, can help bakers consistently control the color and moisture to achieve tighter product specifications. “We also reduce energy and waste through the application of forced convection technologies,” he said.
From a programmable perspective, recipe management at the operators’ fingertips provides one tool for success. That’s especially true if such menu-driven system controls can provide quick adjustments inside the oven to control oven temperature in between product runs, according to Shawn Moye, vice-president of sales, Americas, Reading Bakery Systems.
“As soon as the last product enters the oven, we have an automatic system throttle back the oven, reducing the overall baking profile,” he said. “This helps the oven equilibrate before the next product enters it. By doing this, we reduce product waste and get the oven back to its ideal product profile as quickly as possible. The operators have access to all recipes at the operator interface terminal so that with a touch of a button, they can set the required number of burners, damper positions, oven exhaust, bake times, blowers speeds and anything else directly related to the baking profile.”
The Gemini/W&P menu-driven indirect gas-fired ovens provide stable temperatures and bake times and control of flash heat, said Ken Johnson, president, Gemini Bakery Equipment.
The company offers an oven with a unique turbulence system in which each blower offers variable speed to provide more precision to the baking process. “Airflow is reversible and can be from top-to-bottom or bottom-to-top,” Mr. Johnson said. “This is particularly important for panned product quality where a uniform product top, bottom and sidewall bake is desired.”
Likewise, targeted steam can be delivered directly to the products for minimal waste. “Steam quantity and steam flow direction are variable and manually adjustable,” Mr. Johnson noted. “Steam is supplied to both sides of the oven to assure uniform distribution.” At the same time, he added, moisture evacuation ducts and dampers in each oven zone can be adjusted to profile moisture retention or extraction for each product.
Enhanced durability is another attribute that oven producers will promote during IBIE. In its continuous ovens, AMF Baking Systems uses Emmisshield nano-emissive technology to reduce oven chain heat exposure, ultimately reducing lubrication needs by up to 50%, noted Phil Domenicucci, baking systems manager of the company. Nano-emissive emitter track shields are applied to new and existing ovens, reducing heat reaching the oven chains.
Meanwhile, Stewart offers chain monitoring systems that identify seized and improperly lubricated bearings, greatly increasing both chain and track life.
At the WP Bakery Group USA, advances in technology have resulted in energy savings of 30%, 20% reduction in baking time and 6% less weight loss in product during baking time, according to Patricia Kennedy, president of the company. “We are also integrating the use of artificial intelligence for process controls. One of the areas of efficiency comes with our new heat exchangers,” she said. “The heat continues to exchange above the oven and is brought back into the baking chamber when called for by the baker in the next recipe, usually after steaming. This shortens the temperature drop in the baking chamber, improves bake result with better steaming and saves time and energy.”
In addition to space-saving design ovens, Auto-Bake has engineered a 3-zone oven turbulence system for better baking control. “We pioneered this system within the oven mainframe to achieve more efficient airflows and to minimize heat and gas losses,” noted Paul Hicks, director at the company. “This results in improved baking flexibility and quality at lower energy costs per baked kilogram of product.”
At the Hostess Brands bakery in Emporia, KS, each of the two Auto-Bake ovens have their own thermal oil system to minimize downtime. “Should something happen to one of the thermal oil heaters, one of the lines will still be operational,” noted Jim Diver, director of sales, Dunbar Systems, which collaborated with Auto-Bake on the installation of the ovens. “This maintains individual operating systems and is common on multi-line installations.”
Of course, flexibility is another key factor that bakers will look for at IBIE, according to Franck Ellenbogen, area sales manager, North America, for Mecatherm. The company’s double-action oven with cyclothermic and impingement heat is designed to bake everything from panned bread, brioche, rolls and buns to pies, croissants, puff pastries, pizza and flatbreads.
In the end, the type of oven and the battle for control ultimately depends on bakers’ personal preferences and the type of operations they run. High-volume plants, for instance, tend to require more statistical process controls while many specialty bakers sometimes prefer a different approach.
“Artisan bakers still want to have human intervention,” said Damian Morabito, president, Topos Mondial. “They want to see the color of the product, then make the adjustments. Either way, the industry has made great strides in recent years. We’re giving them a lot more data to monitor the process than ever before.”
It’s just a matter of how they use that information to be better operators in the long run.