Focusing on oven fundamentals
April 25, 2016
by Dan Malovany
It’s not only that there are “smart” ovens these days that can run a production line on automatic, but intelligent operators who understand the thermodynamics of baking and adjust their product flow accordingly. “We advise to schedule wisely,” said Russ Garland, BakeRite president. “Increasing the temperature of the oven is easier than decreasing it.”
That’s because some burners are so powerful that it’s easier to throttle up the temperature than lower it. Over the years, oven designers and engineers have improved insulation and bake chamber seals to make them more energy efficient and provide consistent baking. As a result, during baking, a burner in a direct-fired oven may run at just 50% capacity to maintain the temperature in a specific chamber or zone. During a changeover to another product, that burner can jump to 100%, hit the new set temperature and drop down to 50% capacity to maintain the actual conditions.
“It’s like having the biggest motor on your bass boat so that you can get to the spot on the lake and troll for the big fish,” said Bill Grutter, vice-president, BakeRite Systems.
Changing temperature on indirect-fired or cyclothermic ovens isn’t quite as quick as direct-fired, mainly because the radiant heat comes from tubes or ducts that recirculate air and reheat it to provide a consistent bake. However, by combining the optional forced air convection feature and adjusting the volume of airflow in the tubes or ducts via the dampers, bakers can adjust the conditions inside a zone or chamber within a matter of minutes.
“With the optional Duotherm air convection feature, we can toss a little more air or a little less air on top, or a little more or a little less air on the bottom — or even the front or back of the oven,” observed Damian Morabito, president, Topos Mondial. “If a product is coming out somewhat light, the operator might adjust the dampers to get more heat in the final zone. If the product is getting too much color, the operator can cut back on its convection because that’s the easiest way to instantly adjust the amount of heat the product gets. However, if you make a damper change, it’s going to take a few minutes or even a full bake cycle to adjust the heat in that zone of the oven to where you want it.”
With some systems, such as large open spiral conveyorized ovens, the maximum gap created by a changeover is one baking cycle, although changes in design have made it much easier to tweak temperature to fine-tune product quality.
“Due to the nature of a large open oven, products of dissimilar characteristics cannot bake in the same environment,” said Scott McCally, product manager, thermal group, for Stewart Systems and Baker Thermal Solutions. “The oven is designed to react quickly to parametric changes; however, one parameter that is difficult for most ovens is to move from a high temperature to a significantly lower temperature quickly. When bakers can settle on product bake temperatures that are all ±40°F of each other, they find that they can cut the gap significantly and run products through the oven simultaneously without any compromise in product quality.
“Furthermore,” he continued, “our oven control system moves heat within the chamber by zone control in specific recipe proportions. The total amount of heat supplied at any given moment is determined by the product load requirement. This system greatly reduces the impact that flash heat can have at the beginning and tail end of production gaps.”
Controlling flash heat can be done in several ways. “You certainly improve your success if you schedule similar products baking one after another,” explained Darren Jackson, COO and vice-president of sales and marketing, The Henry Group. “If you’re jumping around with products with various bake temperatures and profiles, you’re only making your job more difficult.”
A good rule of thumb? Look at running similar products and pounds per hour flowing through the oven, Mr. Morabito advised. The more consistent the poundage and oven loading pattern, the fewer adjustments that need to be made.
Moreover, make sure to maintain proper spacing and matrix control. “If you’re going from Kaiser rolls to 12-in. hoagies to 4-in. rolls, as long as you are placing them on the baking hearth in the same pounds per square foot or pounds per hour, you don’t have to play with the temperatures as much to adjust to different products,” Mr. Morabito explained. “Keeping the pounds per hour equal will even work for different product weights and sizes. You need to space out a 3-lb rye loaf a lot further than if you are running hoagies or dinner rolls.”
Computer controls can monitor gaps in the baking process and even reduce changeovers using new auto-cutback routines that continually modulate heat output to the highest possible turn-down and then begin shutting down burners or opening exhaust dampers, noted Phil Domenicucci, baking systems manager, AMF Bakery Systems. “For lower production items such as fewer pounds of dough per hour, the baker can adjust specific burners for less heat output on a per item basis,” he said. “The system is monitored by product tracking and recipe management programs.”