February 1, 2015
by Charlotte Atchley
Product quality drives baking innovation. In the quest to find the most efficient bake for the highest quality product, choosing the proper oven is critical. Armed with that knowledge, bakers can use different technology and techniques to achieve the best bake. Multi-zone and hybrid ovens offer bakers the kind of control and flexibility they need to bump up the quality of baked goods.
Tunnel ovens with multiple zones provide bakers a great deal of versatility as each zone’s temperature, air turbulence and even humidity can be adjusted during specific portions of the baking cycle. “A multi-zone oven allows the baker to create different heating profiles in each zone that should match the needs of product for proper and quality bake over the length of the oven,” explained Damian Morabito, president, Topos Mondial, Pottstown, PA.
For bread, a baker would set up the zones to create a temperature profile that achieves the optimal S-curve, said Phil Domenicucci, executive product manager for thermal products, AMF Bakery Systems, Richmond, VA. In the first zone, to get a greater oven spring without drying out the crust, a baker may choose to have a high bottom temperature. The second zone may also have a slightly higher but even bottom heat to achieve the proper yeast kill temperature. The third and final zone can have slightly lower temperature with more top heat to create color and crust.
A hybrid oven takes this concept a step further by combining various types of heat transfer technology into the same tunnel oven. These combinations typically are direct-gas fired with indirect fired; direct gas-fired and impingement; and indirect fired and impingement.
Where one type of heat may be great for one part of the baking process, it might not be able to deliver all the necessary characteristics bakers are looking for. “For instance, a baker producing crackers needs a substantial amount of radiant heat to develop the cracker flavor characteristics,” said Shawn Moye, vice-president of sales, Americas, Reading Bakery Systems, Robesonia, PA. “Once this is complete, they need to finish baking and drying the product. A hybrid oven offers the most efficient baking platform to achieve these requirements by using direct gas-fired ribbon burner oven zones in the first part of the oven to apply the radiant heat followed by direct convection zones to finish baking and drying the product.”
With this level of efficiency, bakers can achieve the exact finished product characteristics they want and often in less time. “In some cases, it’s possible to shorten bake times by using more efficient methods of applying these thermal characteristics at the right time and in the right proportion,” Mr. Moye said.
Inside the oven
A baking profile consists of three basic steps: the development, set in and final color. The length of time each product spends in each portion of the bake profile impacts the final product’s flavor and texture. In a multi-zone oven, this can simply be a change of temperature, airflow or humidity between each stage; in a hybrid oven, the type of heat can change.
In the first zone, a baker’s goal is to impart oven spring to the product, or for example, in the case of a cracker, begin to develop the cracker dough. It’s a gentler heat that also controls the spread of a wirecut cookie, explained Kevin Knott, technical sales manager, Franz Haas Machinery of America, Inc., Richmond, VA. For this process, direct gas-fired technology does the trick.
“What the bakers are gravitating toward are hybrid ovens, ovens that include a direct gas-fired section providing high-intensity radiant heat, which is great for product lift and blistering typically required for low moisture cookies and crackers followed by a length of convection oven which provides excellent control over final product moisture,” said Brett Cutler, technical services supervisor, Baker Perkins Inc., Grand Rapids, MI.
To prevent the product surface from cracking as it expands in this first zone, Mr. Morabito recommended that this zone can also have steam. This not only prevents cracking but also adds color and results in a less dry crust structure in the final bake.
If, on the other hand, the product demands a slow rise in the beginning of the oven, Charles Foran, chairman, Babbco, Inc., Raynham, MA, suggested indirect-fired or a dead-heat zone combined with convection in the second half of the oven. “It’s no longer a choice of all indirect fire or all convection,” he said. “Using our hybrid technology, you can mix and match multiple oven technologies to get the best results.”
As products move into the second phase of the oven to set up, air movement aids in uniformity. “Radiant heat gives heat from the bottom and top,” explained Stephen Bloom, vice-president of Allied Bakery Equipment, Santa Fe Springs, CA. “If you only have that static technology, it’s hard to get heat evenly to the sides of the product, especially the closer they are together or if they are tall products. If you have air movement, that will bring the heat in between the product.”
Turbulence not only helps create a uniform bake but it also speeds things up. “The air movement strips away the cooler surface layer on the product allowing it to bake quicker,” said Jim Diver, director of sales, Dunbar Systems, Inc., Lemont, IL. By speeding up the bake, the oven can get more throughput.
The last step of the oven imparts the final color onto the product and controls the final moisture content. For this, bakers can rely on indirect-fired or impingement technology. “An indirect-fired baking oven with air turbulence in the end of the oven cycle [in the back end zones] will also give the product a more controlled and uniform bake with the desired color control,” Mr. Morabito said.
Spooner Vicars Bakery Systems, Plano, TX, builds moisture and color control in the design of its hybrid ovens with the direct force convection part of the oven being an impingement design. Air nozzles bring the hot gases closer to the products. “Other convection style ovens use a heat source and fan that moves the hot air into the baking chamber and not directly to the product,” said Jeff McLean, sales manager, North America. “We move the hot air through a series of nozzles to bring it directly to the product, breaking the air barrier around the product.” The low velocity combined with high volume of hot air enables bakers to get control of the final moisture and radiant dampers control color on their baked foods.
While the heat from direct gas-fired ovens may be great for the initial oven spring, a more high-intensity drying heat is necessary for removing the final moisture from a product such as crackers. With some products it can be difficult to remove the moisture without over-coloring. “In many cases, the oven operator has difficulty balancing the correct product color with the correct final moisture content,” said Tim Clark, president and CEO, Radio Frequency Co., Inc., Millis, MA. “The lighter the desired color, the more difficult it is to reach the correct dryness.”
Radio Frequency’s Macrowave dryers address this by preferentially heating directly where the moisture is. This eliminates the need for an excess zone in the oven while bringing uniform moisture levels to challenging products.
Multiple zones provide bakers the ultimate level of control in their ovens. In each zone, the baker can control temperature, humidity and air movement to achieve the perfect baking curve for the specific product.
In the Gashor tunnel oven, represented in the US by Cinch Bakery Equipment, Clifton, NJ, each zone is controlled by a different burner tower instead of one tower for the entire oven. The baker can control each burner tower for the perfect temperature changes throughout the oven.
The PU Integral oven from Koenig Bakery Systems USA, Ashland, VA, features independent baking zones that can be controlled as if they were several single ovens. This allows the baker to establish and follow precise baking curves every step of the baking process. With servo driven technology guiding the oven’s mechanics, each step is fast and controlled, which enables a wide window of possible bake times.
With different types of oven technology combined into one oven, bakers benefit from the controls afforded by both.
“There’s a certain amount of flexibility built into a standard direct gas-fired oven already,” said Geoff Hawley, vice-president of sales, Baker Perkins. “You can control all those burners, the air movement and the exhaust as well as the bake speed. On the convection portion, there’s flexibility to adjust the exhaust, air flow and temperature as all as where do you put air inside the oven.” With Baker Perkins controls, a baker can position air upstream or downstream of the heat source, giving a baker flexibility to adjust for color and moisture as well as improving bake times.
On top of this precision, today’s recipe management systems enable bakers to program their ovens to change the baking profile from product to product. With this level of control, bakers can make a plethora of different baked goods all at specific baking profiles.
The number of zones in a tunnel oven is determined by the size of production as well as the baking parameters, which include temperature, baking time, steam flow, exhaust flow, convection and humidity, according to Mr. Domenicucci.
“The parameters are programed into the recipe to create the best profile for the baking process of a specific product,” he said. “Also, zones might not all be equal in length. In this case the number of parameter changes is governed by the number of zones.”
By adjusting certain aspects of the oven, bakers can control all these variables, according to Jerry Barnes, vice-president of business development and marketing, for both Baker Thermal Solutions and Stewart Systems, subsidiaries of the Middleby Corp., Elgin, IL. Baking time is determined by the conveyor speed while temperature is controlled by heat input. Bakers can set humidity with exhaust speed. Forced convection rate is established through recirculation speed and is useful to set top and bottom color. To manipulate crust characteristics, bakers can use modulated steam injection. They can also control burner selection to optimize heat load with heat input.
While most industrial baking ovens have at least three zones with top and bottom settings for each zone, the more zones the oven has the more discrete the heating control can be during the baking cycles, Mr. Morabito said. “It is all about giving the baker control,” he added. In indirect-fired and air-impingement ovens, the zone controls are adjusted by top and bottom slide dampers. Direct gas-fired ovens offer more finite controls as each individual burner on the top and the bottom can be turned on or off or set as a group to the desired temperature.
One of the biggest advantages of multi-zone and hybrid ovens is the flexibility they offer to precisely bake a variety of products. While bakers can set parameters within each zone, they can also program the oven to remember and automatically set those parameters per the product with the advent of micro-processor based digital and programmable systems, according to Mr. Morabito. This ensures that every product is baked accurately and makes the oven easier for operators to use.
“All settings are preprogrammed and locked in memory of the oven PLC,” Mr. Diver said. “With this said, anyone familiar with the oven controls can operate it.” Auto-Bake’s Wonderware software controls the temperature through sensors in the oven. This program can be linked through the Internet, which enables technicians to troubleshoot electrical issues from remote locations.
Stretching across applications
By employing parameter settings in different zones and multiple types of heat, multi-zone and hybrid ovens offer bakers a new level of flexibility.
For example, by giving the Thermocar combination rack/deck oven the ability to add convection heat to its already radiant heat, Cinch Bakery Equipment gives bakers the ability to produce a wider range of products at a higher quality bake, just with those two types of heat. Toss in more, and the opportunities grow.
These capabilities make it possible to bake the same product differently as well as completely different products, according to Cyril Munsch, director of sales Mecatherm SA, Barembach, France. For instance, lidded tin bread needs convection heat from the top at the beginning of baking. When baked unlidded, the bread needs limited top convection heat as to not dry out. In the same oven, a pizza can take on high convection heat and high temperatures, and puff pastries will require low temperatures and a combination of radiant heat with low convection heat. All of this is possible when technologies are combined.
“A multi-zone oven is a very good investment for a baker,” Mr. Domenicucci said. “It will allow him or her to create different baking profiles for all products from bread, buns, rolls and bagels to sweet goods, cookies and cakes. It offers flexibility and consistency.”
With many bakers wanting to make par-baked, as well as hearth-baked and pan rolls and breads in one oven, Gemini Baking Equipment, Philadelphia, offers the Gemini/WP Thermodor indirect-fired tunnel oven, which allows bakers to quickly change the oven profile to suit either pan or hearth products. The vertical turbulence system enables bakers to change the oven profile quickly. This system can adjust bottom and top heat quickly during the bake cycle and can be used in all zones, according to Mark Rosenberg, CEO, Gemini Baking Equipment.
Each zone also has a manual or automated moisture release/removal feature that comes in handy when baking either fully or par baked hearth or pan products. “It allows an adjustable product-by-product moisture control when baking a wide range of products,” said Ken Johnson, president, Gemini Baking Equipment/KB Systems.
With this level of flexibility, however, comes great responsibility. Bakers must know what products they want to bake and what they need from their oven before moving forward. “You have to make sure your scope has been clearly identified, that the limitations have been identified,” Mr. Knott said. “You also need to know how much capacity you need.” For example, if an oven is 30% direct gas-fired and 70% convection, the bake time on the direct gas-fired is fixed, which with some products may slow down capacity. “To adapt to a different product, the baker may have to bake longer, which could mean a loss of capacity,” he explained.
With its combined range of multi-zone ovens, Baker Thermal Solutions and Stewart Systems can bake panned bread products including hamburger and hot dog buns, 3-lb loaves, slider buns and breadsticks. “The versatility of these ovens allows the bakery to abandon the need to build specialized production lines that do not run at full capacity nor generate the required ROI,” said Scott McCally, product manager, thermal group, Stewart Systems.
With multiple zones and different types of heat, these ovens offer bakers the opportunity for greater flexibility and precision and, as a result, better quality, but it’s important to anticipate the products that will be baked in the oven and what those products’ needs are so the baker and supplier can match the right technology to the baked good.