Oven design, heat source, production management
and throughput are all factors for consideration in
striving for high quality and evenness of baking.
Baking conditions are inherently dynamic–a situation that makes baking consistent products from the beginning of a production cycle to the end a challenge. And as critical as the baking process is, it’s important to recognize that the process begins with dough mixing, says John Squire, district manager, Kaak Group North America, Lithia Springs, Ga.
“An inconsistent dough means the baker will never be able to have real process control in the bakery. Attention to the fl our quality from the mill during seasonal changes and the required adjustments during mixing will enable the baker to begin to control his process,” Squire says. “[Other] factors, such as proper water temperatures, monitoring fl our temperatures and mix times [also] are important. Seasonal adjustments in the bake process are often needed due to changes in seasons as the humidity in the air is different winter to summer.”
rough trial and error, bakers determine proper set points and controls for the baking process. But operators often must react to changing conditions, such as production stoppages and variances in load demands. Bakers also are faced with multiple changeovers. Unless the oven is emptied out completely between changeovers, product might end up overbaked or underbaked. That’s where production management plays a role. “ ere is such a thing as feathering, where you slowly increase the [conveyor] speed or decrease it, and you can change the temperature slowly,” says Geri Walker, president, Bake-Tech, Tucker, Ga. “Ideally, you have to empty the oven out.”
Bakers currently may bake their products in older-style ovens where there is limited opportunity to adjust to changing process conditions. But those in the market for a new oven may consider the multitude of technologies available for producing high-quality, consistent products based on the bakers’ product mix, desired throughput, available footprint, growth plans, available energy source and numerous other criteria.
Solving the lateral heat problem
“In the past, it was difficult to get consistent baking because as product moved through each of four zones in a typical 100-ft. oven, the lateral temperature, or temperature across the oven, would vary,” says Jim Diver, V.P. operations, Dunbar Systems Inc., Lemont, Ill.
“In other words, how do I get the same heat on this side where my gas is coming in, versus the far end where maybe I lost all my gas and used it across the burner,” Diver says. “[In newer oven models], you have an orifice that’s adjustable, which uses minimal gas [at one end], and opens up so you get more gas down at the opposite end. e issue that comes up with lateral heat is that you can look at [one] side and see it is dark brown, while [the other] side is light. at would be a direct-fired oven. You try to get balance. Various burner manufacturers have come up with different devices to adjust their lateral heat by adjusting the amount of gas flow that’s going through that tube.”
Commercial bakery ovens vary in construction design, footprint and method of heating, among other parameters. Energy sources used to heat ovens include electric, gas, thermal oil and infrared. Ovens also are heated by convection, or circulating hot air.
“Electricity is the most expensive fuel for baking. It’s convenient and easy for a small operation to use without the expense of a thermal oil system to pipe in,” Diver says.
Yet more bakers are turning to thermal oil as an energy source as concerns about carbon emissions increase. Thermal oil requires the least amount of energy for recovery. For instance, at Tasty Baking Co., Philadelphia, five newly installed Auto-Bake ovens use thermal oil that only require 5° F reheating on the return, Diver notes. Thermal oil gives consistent bake for all products. You don’t have to worry about light or dark product or lateral heat, he adds.
But Walker feels gas burners are the way to go. Gas responds immediately, whether it’s the beginning of a production run, the end or a line stoppage. “You have to be able to shut that heat off,” Walker says.
Flash heat, or a sudden burst of energy, can occur in ovens, particularly during short runs or large gaps in production. “Kaak’s MCS oven has a unique feature where it registers a gap in production so as not to create an improper bake. Often, bakers will load empty straps in the oven before and after a short run to absorb the heat and not flash the product,” Squire says.
In the old days, bakers would run pans with bricks or water in them to soak up the flash heat, Walker adds.
A wide variety of ovens exist for bakers, including tunnel ovens, rack ovens and deck ovens. But it’s the continuous oven that’s synonymous with consistent baking, Walker says. When a tunnel oven is loaded with seven pans on a 12-ft. tray, heat has to be applied evenly across all pans. In a continuous system, the width is not 12 feet, but three feet. “We group pans in groups of one as opposed to seven,” Walker says.
The continuous oven uses an endless type of conveyor system. Burners sit under the conveyor in the straight lengths. Air can be in the curves, straights, or recirculated via ceiling fans. The air blows consistently and helps even out the heat to the pan, he adds.
“Burners are parallel to the conveyor, and are typically 10 feet to 20 feet long. The burners run parallel under the pan and light the pan from right to left as it is conveyed down the oven. The front end of the burner may be on the right side of the pan and the tail end of the burner is on the other side of the pan. Sometimes there are burners on both sides of the pan,” Walker adds.
“Another point about a continuous system is you don’t have a lot of mass to heat. You have the conveyor system, while in a tray or tunnel oven, you have trays that are massive. The trays hold a lot of heat, so they take a while to heat up and take a while to cool off. They’re slow to change,” Walker says. “Basically, the product goes in and the burners respond to the load. The consistency you get out of a continuous system is superior to what is physically possible in a tray or a tunnel oven, just because of the mass.”
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Auto-Bake’s continuous solution is its Serpentine tunnel oven, which has the unique advantage of having one-tenth the footprint of an equivalent tunnel oven. “The Auto-Bake line is as versatile as any other line would be,” Diver says. Bakers can use Auto-Bake’s standard “contained pan” model or its “free pan” transport interface, which allows bakers to use their own standard pans–whether they’re cake pans, loaf pans or cupcake pans.
As Diver points out, "One of the benefits of using the captured pan with the Auto-Bake oven, is I can [produce consistent product at] very high speeds and I don’t have the issue of pans being separated from the system; meaning I don’t have accumulation issues and I don’t have pan damage issues, when the pan is now part of the system. I’m really set for high-speed cake production."
In an article entitled “A comparison of deck oven designs,” by Stephan Wechsler, president, Empire Bakery Equipment, Hicksville, N.Y., Wechsler states that the major differences between the five gas/oil-fired stone hearth deck ovens he describes are how heat is distributed and the type of construction materials used.
In the cyclothermic oven, hot gases move between and around decks through a heat exchanger or a burner. A powerful fan circulates air. These ovens are typically constructed with steel and a mineral wool-type insulation, Walker says. Some cyclothermic ovens can regulate one temperature on the top one or two decks and another on the bottom decks, which can accommodate a varied product mix.
“These ovens aren’t usually recommended for baking heavy products. As with a hot air heating system in a home, when the burner shuts off, there is a tendency for the oven to cool down rapidly until the thermostat calls for more heat. Then when the burner reignites or goes back to high flame, the temperature will rise again quickly. This produces more temperature fluctuation than might be desired for baking larger breads with longer bake times, especially if you are using steam and desire a good crust,” Wechsler explains.
Because cyclothermic ovens can cause more water to be baked out of free-standing products than thermal oil ovens, it is more suitable for pan breads, Squire says.
Wechsler also discusses vapor tube ovens including all steel “ring tube” models; steel and cement construction and cement lined vapor tube ovens “for the ultimate in brick oven baking”; and thermal oil ovens.
In vapor tube ovens, for instance, no moving parts or fans are used to distribute the heat. Thus, baking consistency is achieved from deck to deck and side to side. Yet, differences exist among the three models because of the construction materials used. All-steel construction vapor tube deck ovens, which circulate steam through a series of tubes that surround the oven and run between decks, were installed in the United States for many years. “As demand for hearth breads has increased, however, many bakeries find that an all-steel oven has less ability to maintain the best heat necessary for high production baking and steaming. This can result in a greater change in baking properties or unevenness of baking after six hours or so of heavy production,” Wechsler says.
Vapor tube ovens made steel, cement and brick, commonly used in European bakeries, “offer the best balance between heat retention, efficiency and flexibility of temperature, Wechsler adds. “These ovens utilize brick and cement in the fire chamber, which acts as a ‘heat sink.’ …When the oven is loaded with bread and steam is introduced in the chamber, absorbing the chamber’s available heat, the brick and cement supply a continuous, smooth flow of heat without the burner having to try and play ‘catch up.’”
Bakers have much to consider when striving for baking consistency. When it’s time to purchase a new oven for your bakery, bakers should work closely with their supplier to ensure they achieve their goal in producing high-quality, consistent products from the beginning to the end of each production run.
Heat versus temperature
To a certain extent, product is baked with temperature from the surrounding air, which heats up the pan, says Geri Walker, president, Bake-Tech, Tucker, Ga. To another extent, product is baked with a flame from the burner. The tip of the flame is about 1500° F. Air in the oven is about 400 F to 500° F. Therefore, a lot more heat value comes out of the burners. Separate heat zones within the oven are dependent on what the burners are doing– if the burners are full flame, low fire or in some cases, if they’re off. Most of the baking process depends on heat generated from the burner, not the air temperature. For all ovens, temperature can be read, but not the heat, Walker adds.
“In continuous ovens, we have a method of measuring heat. Our method is to put burners on under the pan, heat the pan up and whatever’s leftover we’re measuring as temperature. But the pan soaks up a lot of heat. We don’t see that part. We’re only measuring what the air took on. We have to use temperature to tell us when we’ve got too much heat and when to throttle back the burners. For example, [when there’s a production gap], the thermocouple will detect a rise in temperature indicating [an absence of product] soaking up the heat, so then you’ll throttle back the burners. The use of temperature to control the oven is valid, it’s just not the whole picture.”