Ovens: A battle for control

by Dan Malovany
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While a little bit of knowledge can be a dangerous thing, not having enough of it can be a costly lesson. That’s especially the case when it comes to ovens. Despite all of the advances in technology, knowing too little too late in the baking process continues to happen today. All too often, by the time operators stroll over to the oven discharge and discover something’s out of spec, the over- or under-baked goods are filling the cooler and even entering the packaging department at an alarming rate.

To take a proactive approach to controlling waste and improving the yield throughout the baking process, a growing number of bakers now rely on proportional-integral-derivative (PID) loop control programs. With this statistics-based technology, a programmable logic controller (PLC) continuously calculates an error value or variances between the desired baking set point against the actual baking temperature throughout the oven. If the actual temperature swings beyond the acceptable, or green, zone and curves into a yellow or red area where it’s too hot or too cold, the oven or its various zones can be adjusted — often automatically — to ensure proper baking conditions.

During the initial set-up of the oven, bakers and snack producers often rely on oven profiling units to balance the oven-heating methods to control consistency and reduce waste, according to Shawn Moye, vice-president of sales, Americas, Reading Bakery Systems. The operators are then given constant feedback at the operator interface terminals by monitoring the PID loop through the PLC via thermocouples located throughout different areas of the oven. “This process can be further enhanced by controlling the oven gas flow as it relates to the volume of product being produced, thus ensuring a consistent BTU input to the oven,” he noted.

The key to the latest in advanced auto-tuned PID programs involves their ability to continuously monitor the temperature curves to maintain an even temperature throughout the baking chamber. 

“Product tracking of each pan in the oven, working with independent zone control, allows the oven to automatically adjust required heat — even with skips, gaps or dwells,” explained Phil Domenicucci, baking systems manager, AMF Bakery Systems.

In many cases, when the oven heats up too much — a situation that can happen especially during gaps in production — automatic cut-backs, or reductions, in the burner ribbons on direct-fired ovens can ensure even baking while reducing energy consumption, noted Ken Hagedorn, vice-president of sales and partner, Naegele Bakery Systems, which represents The Kaak Group in the US.

Having real-time PLC control of the oven is critical in multi-zone ovens where products require a specific baking curve, such as setting the structure for bread or buns in the first zone, establishing the internal texture in the second and determining the final color of the crust in the third zone. “[Controllers] can also document the history of the production runs,” Mr. Hagedorn said, allowing a bakery to track the consistency of the bake cycle per shift and search for ways to achieve continuous improvement of the process going forward.

In addition to using PID loops to bring greater accuracy to baking, closely monitoring baking temperatures has become even more important under new Food Safety Modernization Act (FSMA) regulations. Bakers must validate that their ovens actually kill off harmful microbes by authenticating the kill step in the baking process. AIB International is currently in the process of validating the kill step for baked goods.  “In anticipation of what research AIB International is doing on the kill step, if the industry decides to use it as a part of their food quality assurance protocol, we’re already making that data available to our customers as a standard feature — whether they are using it now or need it in the future,” said Bill Grutter, vice-president, BakeRite Systems.

To provide even greater control while reducing labor, a vision system can be placed at the oven discharge to provide feedback regarding product shape and color. “The vision system can be tied into the oven control system to eliminate the need for an oven operator,” suggested Charles Foran, chairman, Babbco Inc.

“The system can provide a warning or alarm when products are outside of the allowable limits,” he added. “The system has the ability to maintain a library of product photos that can be reviewed in the future. It can also be tied into a product dump or reject conveyor, which also helps eliminate the need for an oven operator.”

WP Bakery Group USA’s recipe management function in the systems’s controller allows for up to 200 recipes with 20 baking steps, according to Patricia Kennedy, president of the company. The function control includes time by step, temperature by step, steam, fan speed and damper control.
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