Mixers knead with intelligence
Sept. 1, 2015
by Charlotte Atchley
The further the baking industry delves into the science of dough development, the more control bakers can exert over the breads, buns and rolls they make. With the range of products diversifying from just basic white or whole wheat bread to include artisan, flatbread and other ethnic baked goods, this knowledge is crucial for bakers trying to consistently turn out a wide variety of products. Armed with intimate knowledge of how these doughs form, bakers can ensure quality and consistency. That quality and consistency is created, along with the dough, in the mixer.
“The understanding of the mixing process has made a great leap forward in the past 10 years,” said Jim Warren, vice-president, Exact Mixing, Reading Bakery Equipment, Robesonia, PA. “As products become more diverse and consumers more demanding, the mixing process has become more complicated. Terms like shear rate, hydration rate, hydration efficiency, energy input, and a long list of others have required mixer manufacturers to look closely at their designs.”
Mixing means more than just add ingredients and hit start. With the knowledge of how different doughs develop and what they need to come out just right, mixer suppliers have altered the design of their equipment, and bakers have altered their mixing strategies to get the best dough development in the most efficient way.
First, not all doughs are created equal. Various doughs have different requirements from the mixer, whether that’s changing roller bar positions, rpm speeds or cooling needs. “Inside the mixer, you want to make sure you’re kneading and not having the dough wrap around the roller and go for a ride,” explained Damian Morabito, president, Topos Mondial, Pottstown, PA. “You need to create a stretch, fold and knead action with the roller bar mixers.” Creating the proper kneading action to suit the dough being mixed requires proper bowl and agitator geometry.
Second, understanding about gas cell creation and sustainability has changed the way bakers and mixer suppliers view what happens in the mixing bowl. “The importance of the gas bubbles shows itself later on in the process, in the structure of the dough and how it stands up to downstream processing through dividing and rounding,” said Rob Francis, chief engineer for bakery, Baker Perkins Inc., Peterborough, UK. “The more gas bubbles you have, particularly for pan bread, the stronger the structure, and that reflects in final product shape, size, volume and crumb texture.” Those gas cells are created in the mixer, and by creating a better gas cell structure in the mixing stage, bakers can reap benefits in better processing and final product quality.
Better understanding of hydration has also contributed to more consistent product quality and improved shelf life. With the right controls, bakers can implement all these principles to maximum effect.
Different mix for different doughs
Every dough is different, and they should be treated as such in the mixer. As the types of products bakers make diversify, so must mixers diversify to handle each dough’s individual needs. “Mixers must account for hydration, mixing and development stages separately to remain as versatile as possible,” Mr. Warren said. “Changeovers must be quicker and sanitation easier. Future dough mixers must account even more for these demands.”
Each dough needs to be kneaded and stretched, but how a dough is best kneaded and stretched is determined by its absorption. The difference between a high-absorption, slack dough and a stiffer dough cannot be ignored, and they do not mix the same.
“High-absorption or slack doughs require a mixer cooling solution that will produce a dough that is more easily and accurately machined down the line,” said Terry Bartsch, vice-president of sales, Shaffer Mixing, a Bundy Baking Solution, Urbana, OH. These cooling systems can come in the form of a refrigerated bowl, bowl ends or a refrigerated agitator. “Conversely, stiff doughs, which we have seen with some high-gluten, wheat doughs, and bagel products require more power to mix properly,” he said. “Mixers for these types of doughs require increased horsepower.”
Matching the proper kneading to the dough’s stiffness and absorption is all in bowl and agitator design. “For different absorption doughs, the mixer should be configured differently and the mixing rpm should be different,” Mr. Morabito said.
This translates to roller bar positions and rpm speeds varying according to the dough absorption. For soft doughs, the mixer can knead and stretch the dough at a higher speed, but at those same speeds, a firmer dough will wrap around the agitator and be tossed around the bowl. “It’s very inefficient to go around three or four times and not really be mixing, stretching folding or kneading,” he said. “At slower agitator speeds, the dough can fall out of the center and get kneaded properly.” To accommodate these varying absorption levels and bakers’ ever-present need for flexible equipment, Topos Mondial’s mixers feature adjustable roller bar positioning and variable frequency drives (VFD) that give bakers control over agitator speed and the agitator to bowl geometry.
Suiting the mixer design to the mixing action also improves efficiency. By ensuring that the mixing action occurring will properly develop the dough inside the mixing chamber, the mixing can happen quickly with minimal energy, heat and time. Improved bowl and agitator design improves efficiency and passes other benefits down the line. AMF Bakery Systems’ research into mixer designs has led the company to make its own improvements to its batch dough mixers. “This allows mixers to increase throughput, but even more importantly decrease mix times,” said Larry Gore, director of sales, AMF Bakery Systems, Richmond, VA. “The increased throughput allows the mixers to increase yield from the same production hours. The decreased mix time allows for product improvements as you can run smaller batches at more batches per hour. This can improve product quality by allowing the baker to supply fresher dough to the makeup equipment.”
Building the scaffolding
The structure of the dough, what is being developed in that mixing bowl, is of the utmost importance. Gas trapped by the gluten matrix woven together through the mixing action will ultimately give the final bread its shape and texture and even determine the batch’s volume. The control of atmospheric pressure in the mixing chamber can enable bakers to get the most from these gas cells.
“The mixer is the best place to create the best structure,” Mr. Francis said. A pressure vacuum in the mixing chamber controls the size of the gas cells by bringing in more oxygen into the chamber. This increases the functionality of ascorbic acid and other ingredients in the dough that may need oxygen, which will, in the end, impact the final product’s texture and crumb.
While the gluten matrix holds these gas cells together, the ascorbic acid strengthens those cells. “It’s like scaffolding,” said Andrew McIlwrick, process technologists for bakery, Baker Perkins. “The gluten matrix is strengthened by the ascorbic acid, so you end up with more cells.” That ascorbic acid needs the extra oxygen to improve its functionality. Baker Perkins’ pressurized mixing chamber draws extra air into the mixing chamber to help bakers take control of their dough’s structure.
To take advantage of the opportunities pressure adjustments and oxygen availability offer bakers, VMI, Montaigu, France, developed a kneader prototype on which bakers can conduct trials of different types of dough. By understanding the effects of pressure changes during kneading, operators can modulate the final dough aeration and volume of bread.
Of course, this all happens very quickly. “The entrapment of the oxygen is very rapid and the gluten matrix is also very rapid,” Mr. Francis said. Mix times happen between two and five minutes, with smaller batches being turned out more often to keep up with throughput.
While this process has been standard in the UK, continental Europe, South Africa and Australia for some time, the US relies on mainly horizontal bar mixers to mix large batches of straight doughs. Oxygen is still being drawn into the dough through the action of the roller bar, and the dough is still being developed. However, as the clean label trend continues, Mr. Francis expects US bread bakers may become more interested in the Chorleywood process. “If changes come to the ingredients that can be used, then that will force everyone to look at mixing in a slightly different way,” Mr. Francis said.
Hydrated to the max
Hydration is another key aspect of mixing that may lead to better final products. Fully hydrated doughs mean more homogenized doughs improve quality. This comes into play heavily with artisan breads and those baked goods made with a cleaner label, according to Stephen Bloom, vice-president, Allied Bakery Equipment, Santa Fe Springs, CA.
“Customers are asking for products with fewer improvers and conditioners without compromising flavor,” he said. This can be achieved through better hydration and dough development. The Hydra technology by Sancassiano, represented in the US by Allied Bakery Equipment, delivers such hydration and gluten development.
Hydration is the easiest way to increase yields, according to Denny Vincent, Advanced Food Systems, Columbus, OH. “Companies are looking at improving their yields, and one way to do that is by increasing your water levels in your dough because it’s the cheapest ingredient,” he said. Because of the amount of energy Advanced Food Systems’ mixers impart on the dough, formulations typically require more water.
Pre-hydrating ingredients can deliver benefits of improved hydration as well. “Pre-hydration of flour before the mixing process plays a major role in the dough quality,” said Stephen Marquardt, sales director, food, North, Central and South America, Zeppelin Systems USA, Odessa, FL. Pre-hydrating ensures the flour is fully hydrated and can meet its full potential in the mixer.
Zeppelin’s DymoMix moistens flour with centrifugal force and can vary between a baker’s percentage of 110 and 250. “Within seconds you will have a pre-
hydrated homogenized dough, which you can add either to a batch or continuous mixer,” Mr. Marquardt said.
Rapidojet, represented in the US by Bakery Concepts, Mechanicsburg, PA, hydrates any dry ingredient instantly from 50% to 350% or more. Instead of using mechanical tools to develop gluten and hydrate dry ingredients, a pressurized stream of wet ingredients is combined with free-flowing dry ingredients. The combination of these instantly binds the liquid and dry ingredients for maximum hydration. This not only cuts down on mix time, energy costs and dough conditioners but also increases hydration, yield, quality and shelf life. “Because the dries and liquids are more homogenously bound, we have much better shelf life because we’ve virtually stopped the starch retrogradation,” said Ken Schwenger, president, Bakery Concepts.
All of this higher understanding of dough development grants bakers the ability to better control different aspects of the process. Temperature control, energy and ingredient scaling all play a role in the final dough’s structure, which will have ramifications down the line.
“Adjustments need to be made automatically to control energy input in various stages of mixing, dough temperature, variations in flour quality and other factors,” Mr. Warren said. “This will be a trend that will be critical to product consistency and quality.”
Temperature and energy, those are the most important parameters in Mr. Vincent’s eyes. Monitoring allows bakers to exercise control on both of them. “There are ways to monitor the progress of a dough batch as it’s mixed,” he said. “That’s had a big impact on baking.”
As dough is mixed by an agitator, friction and energy raise the dough’s temperature. To preserve quality and machinability, that temperature needs to be regulated. If the mixer is designed to efficiently mix the dough, temperature control should become less of an issue. “When you optimize the kneading action through speed and roller bar gap, you can drastically reduce your cooling needs, which saves a lot of energy,” Mr. Morabito explained. “You’re not beating it up or taking it for a ride. You’re not putting heat into it, so you don’t have to worry about getting it out.” Jacketing the mixing bowl or chamber is the most standard way to control the dough temperature, but agitators can also be cooled to deliver temperature control.
Sancassiano’s Kyros technology is a vertical mixer cooled with a jacketed bowl. This mixer works best with laminated doughs, which require low temperatures, as well as frozen baked goods or straight doughs for white bread.
The most important aspect of control, however, has to be the mixing speed, which bakers manage with the use of a VFD. “Now, instead of having just one or two mixing speeds preset, bakers can customize mixing speeds to provide their optimal product and potentially shorten mixing times,” Mr. Bartsch said. VFDs also save energy with a built-in soft start feature, which eliminates sharp energy draws when a mixer starts or changes speeds, he continued.
Bakers can use the VFDs to their advantage by programming different mix speeds for different times with each individual product. They can even go so far as to program what is meant by the low speed rpm or high speed rpm. To get an even, more consistent dough more efficiently, which will cut down on energy usage, smart controls can mix the dough to an energy curve instead of by time. The mixer will mix to a certain energy level, and when reached, it will know the dough is properly kneaded. “The controls can monitor energy usage and stop mixing so you don’t overmix or undermix,” Mr. Morabito said.
Mixing up speeds
Being able to use a variety of mixing speeds from the VFD and program them into the recipe on the PLC is important in this environment of developing multiple kinds of dough. “Depending on the protein levels and hydration rates, we can determine a specific mixing profile to create that development in the optimum time,” Mr. Francis said of Baker Perkins’ VFD capabilities. “You are mechanically developing that gluten structure, so you want to put the energy you’re using from the mixer drive into that dough as efficiently and rapidly as you can.”
This also cuts down on energy usage and costs. AMF implemented high-efficiency AC drives and efficient drive designs, which have allowed for better mixing control and therefore reducing power usage.
Mr. Bloom noted the benefits of being able to monitor energy absorption. “Metering the energy absorption during the mix is a very effective way to control quality and, especially, consistency of the product,” he said. Sancassiano designs its mixers with this feature, which allows operators to store mixing data on USB drives or the bakery computer system for quick feedback.
Recording this information is also important in managing the bakery’s performance and making notes of how production can improve. Oshikiri USA offers dough development monitors that show and log all the mixing characteristics. “This will allow records showing that the quality is maintained,” said Tim McCalip, general manager, Oshikiri USA.
A uniform dough starts with proper ingredient scaling, and PLCs can help with that, too. “You want a consistent dough, and you’re only going to get that if all the ingredients coming into the mixer are consistently measured and weighed,” Mr. Francis said.
Baker Perkins offers an ingredient weighing system with its mixer. This integrated control measures ingredients based on percentages to ensure that the ingredient scaling is always proportional to the flour being used.
Topos Mondial’s mixer controls can coordinate with bulk ingredient handling systems as well as the dough delivery systems on the other end of the mixing bowl. “It can either take control or handshake with those controls,” Mr. Morabito explained. The mixer can request ingredients from the ingredient handling system through a simple Ethernet connection.
Zeppelin Systems uses PRISMA management system to document every recipe change and track every batch and raw material. “This provides a maximum of security as it enables production managers to react quickly if necessary,” Mr. Marquardt said. “In continuous mixing systems, constant control of all raw material infeed is crucial to guarantee a consistent quality in the final product.”
By automating this process, bakers can be sure that the ingredients coming into the mixer are always in exact measurements.
As knowledge of dough development expands, bakers and mixer suppliers can use those findings to better understand what exactly is happening in the mixing bowl and make adjustments to achieve the best product possible.