Ovens controlling consistency
Aug. 1, 2012
by Shane Whitaker
Baking brings out flavors and imparts color and vitality in pale, lifeless dough. Time and temperature represent the process’ two main variables that bakers must control to ensure consistency. However, bakers also have to monitor moisture and maintain constant heat across large expanses. Ovens often use turbulence to improve bake qualities and reduce bake times, yet this also has to be applied and controlled properly.
Ovens feature complex environments that can be difficult to manage. “Ideally at the operator level, the controls are simplified to selecting a product code and running or stopping product,” said Scott McCally, mechanical engineer of thermal products, Stewart Systems, Plano, TX. “Beyond that, the operator’s console should primarily serve as a monitoring station.”
However, he added, “every customer has a different theory about the level of control afforded to their operators, and our system allows for endless empowerment flexibility.”
At a minimum, ovens should have direct spark ignition (DSI), AMF’s standard burner control, according to Phil Domenicucci, executive product manager for thermal products, AMF Bakery Systems, Richmond, VA. “The cost of DSI is no longer prohibitive and should be on every oven for convenience and safety,” he said.
With DSI, each individual burner controller is wired directly or via quick disconnects to a distributed I/O connection box for each heating zone. Each connection box has an Ethernet connection to the control panel and programmable logic controller (PLC).
Bakeries manage the zone profiles using AMF’s Recipe Management System with product tracking. “This allows the baker to enter all the product parameters such as baking temperature, time, steam, convection, pan size and loading into one screen,” Mr. Domenicucci said. “Recipe management will automatically set up the oven parameters, providing consistency.”
Alerting when altered
Consistency — there’s that word again. Whether baking large wholesale orders or smaller production runs, bakers desire uniformly baked products. “Oven performance should be measured by the consistency of the baked product across the pan and from pan to pan, beginning at the first pan into the oven and ending at the last pan out of the oven, for any given product run on any given day at any given hour,” Mr. McCally said.
While that may sound simple enough, conditions within bakeries vary and change. “While ovens inherently perform best in a steady-state environment, such an environment is often short-lived inside a bakery,” he said. “Factors such as intermittent product throughput, inconsistent ingredient formulation and bakery HVAC operation can greatly impact oven performance.”
Line operators may need to tweak an oven’s settings to compensate for environmental changes to ensure consistency even when it’s tuned to the “golden recipe,” as Charles Foran, president of C.H. Babb Co., Inc., Raynham, MA, referred to the optimal baking profile for each product code set by R&D.
If an oven’s settings are altered greater than limits allowed by the bakery, the control system automatically sends email alerts to those who need to know these changes have been made, he said. While PLCs come standard on its ovens, today C.H. Babb offers a management data collection and custom report system, which gives bakeries the level of control they need for recipe management. Also, he noted that the system’s operator interface terminal (OIT) often includes a 15-in color touch screen.
Bakeries can operate more efficiently as they track oven data. “Trending oven variables captured by the PLC allow operators assistance in baking profiles, maintenance personnel troubleshooting tools to diagnose problems and supervisors to monitor product throughput,” said Travis Getz, director of engineering at Reading Bakery Systems, Robesonia, PA. “This data set can be viewed in real-time and/or stored for future review.”
Depending on the number of burners in an oven, he said, some bakeries will opt for individual burner control to improve performance and efficiencies. “For example, a direct-gas-fired oven may have 200 individual ribbon burners,” Mr. Getz explained. “The settings of these burners may be challenging for an operator to manage for various products. If individual burner controls are provided, the operator would manage these burner set points through the PLC recipe management system.”
Typically, Reading’s ovens include a PLC and OIT. “These devices allow the operator to control the oven through a series of screens as well as provide information about the oven,” Mr. Getz said.
The PLC manages the discrete and analog inputs and outputs, communication to the OIT, variable-frequency drives, and thermocouple cards for temperature control, he added.
Stewart Systems’ customers can select almost any interface and then manage their oven’s control functions by product code via a customizable OIT. Its controls optimize the oven to bake on demand using a derivative approach that best monitors and compensates for performance inhibitors, Mr. McCally said. “Measuring baking efficiency as unit energy per unit weight — Btu per lb — our ovens have produced field data under typical operating conditions that lead the industry in baking efficiency,” he added. “Efficiency, much like performance, is best achieved by maintaining steady-state conditions inside and outside of the oven environment.”
In addition, Stewart Systems’ ovens can feature a variety of optional equipment including steam tunnels, humidity controls or top Coloraiders based on the type of products bakeries bake and the level of product control flexibility that they desire, Mr. McCally said.
With AMF ovens, Mr. Domenicucci said, bakers can choose the level of control by adding options such as recipe management, chain management, quick disconnect, convection and Emisshield emitters.
Convection allows for versatility within the oven, according to Darren Jackson, COO of The Henry Group, Greenville, TX, because bakers can use different zone profiles depending on the characteristics of the product that they want to achieve. “And it can really speed baking times as bakers try to get more products through their ovens,” he said.
Opportunely, convection also lends ability to control oven temperatures, Mr. Jackson suggested. “If you have convection, you can control heat at the top and bottom and by zone,” he said. “By controlling convection, you have maximum control, and the oven can do just about anything you want it to do.”
Impingement adds versatility
Beyond convection, which moves air at speeds ranging from 0 to 1,000 ft per minute, ovens also employ air impingement. To rapidly transfer heat to the surface of products, impingement ovens move air through orifices at much higher velocities— typically 1,000 to 10,000 ft per minute.
Impingement ovens can bake nearly every baked food and significantly reduce dwell times, according to James Padilla, director of product development, Heat and Control, Hayward, CA.
With Heat and Control’s AirForce impingement ovens, bakers control air distribution patterns that deliver dry or a combination of dry and moist air to the surface of product. “You have independent control of temperature, moisture and dwell time,” Mr. Padilla said. “By manipulating those process parameters, you are able to achieve within one oven using the same base product a variety of different looks. You can really manipulate the cooking atmosphere around that product.”
With air impingement ovens, bakers can manipulate airflow within sections of the oven to achieve particular product characteristics.
In addition to tracking baking conditions in the oven, AMF offers a system to continually monitor oven chains for length and displacement during the baking cycle. “Each time the oven is started, the cold chain is measured and recorded,” Mr. Domenicucci said. “The chain length is continually monitored during the heat up phase and baking time. The difference in wear of the chain is reported at the end of the each day, and finally, each year to determine the total annual wear. In addition, the chain Guardian system has a predictive lubrication system with alarms.”
C.H. Babb’s advanced controls also monitor oven environments and alert operators if mechanical issues arise. For example, Mr. Foran explained how an email alert could be sent, warning of excessive vibration at a recirculation fan. The maintenance operator could pull up that alert as well as the maintenance manual explaining how to address the problem right on the line at the OTI. “He is then able to go in and fix the problem before the oven goes down,” Mr. Foran said.
If an oven isn’t running, the bakery isn’t making money. Oven uptime is key — so much so, in fact, C.H. Babb warranties its ovens based on availability, he said. If the company guarantees a new oven will be available 99% but the bakery says it was only available 96% of the time, C.H. Babb’s advanced control systems allow thorough examination to determine exactly why the oven’s uptime wasn’t greater.
Although it’s been said for years that baking’s two main variables are time and temperature, bakers can get a much greater picture of what is actually happening during the baking process using today’s advanced control systems.