Stretch, fold and then repeat. These actions describe how bakers manually develop dough on a bench and also represent the process that equipment manufacturers try to duplicate inside triple-roller-bar horizontal mixers. Kneading, accomplished by all that stretching and folding, is especially critical.
“We should be calling them dough kneaders, not mixers,” said Damian Morabito, president, Topos Mondial Corp., Pottstown, PA. “After ingredients are incorporated, the purpose of the mixer is to knead the dough to get full gluten development and to get absorption.
“A lot of people fail to recognize that the dough has to knead in the bowl, not mix,” Mr. Morabito continued. “There’s a big difference. A mixer is just a high-speed bowl chopper, and bakers might as well put their ingredients in an oversized Cuisinart if that’s all they want. But to properly develop yeast-raised dough, bakeries have to get the correct kneading action. It also has to be done at the right speed, where kneading replicates the actions of a baker working on a bench.”
Through its research, he said, Topos, which sold its first new horizontal mixer in 2009, learned that many bakeries mix too fast. Therefore, Mr. Morabito stressed, bakeries often can slow down agitators, reducing RPMs, while at the same time decreasing mix times 10 to 30%. The relationships between mixing speed, bowl shape and agitator configuration are key, he added.
To this end, Topos made one of the roller bars in its horizontal mixers adjustable, so bakeries can move it either closer or farther away from the side of the bowl, depending on the dough type. The bar can assume eight different positions, and once the bakery finds the location that works for all of its doughs, then it can play with speeds to achieve proper absorption, Mr. Morabito said.
AMF Bakery Systems, Richmond, VA, developed adjustable shear gap profiles for different dough types, according to Bruce Campbell, dough systems product manager. “The shear gap is a critical factor in the efficiency of the mixing cycle,” Mr. Campbell said. “This combined with proper breaker bar placement and secondary agitator size can significantly reduce overall mix cycle time. Variable-speed agitators also provide the flexibility to use different speeds, accelerations and times to enhance mix cycles and development.”
Variable-frequency drives (VFDs) allow bakers to precisely adjust agitator speeds to optimize dough characteristics. Although VFDs have been around for years, they have now become the standard, according to Terry Bartsch, vice-president, sales, Shaffer Manufacturing, a Bundy Baking Solutions company, Urbana, OH. “Five years ago, less than 20% of mixers sold used a VFD,” Mr. Bartsch said “In 2011, 100% of mixers we sold utilized this technology. Benefits of this technology include less wear and tear on drive components and more flexibility with agitator mixing speeds and jog/discharge speeds. Spare parts are also more readily available and less expensive for VFDs versus 2-speed motors.”
Additionally, the cost differential between 2-speed motors and VFDs has become substantially smaller, according to Ed Fay, president of CMC America, Joliet, IL, which now includes VFDs in the base price for all of its mixers.
While bakers save energy costs using VFDs, Mr. Fay pointed out additional economic benefits. “When belt drives, sprockets and chains are shocked to life and to a stop with a 2-speed motor, there is wear and tear on mechanical components,” he said. “However, if you are able to ramp up speed or ramp down to a stop, it’s better for all the mechanical components.”
Most new high-speed bread and bun lines fully automate their horizontal mixers; therefore, bakers must know the process before, during and after final mixing, according to Mr. Campbell. “Dough Guardian from AMF gives the baker that data and control,” he said. This control system measures and records temperature of the dough, sponge, water and flour. It also monitors the energy consumed by the mixer, the glycol coolant’s temperature, and pressure in and out of the bowl.
Dough Guardian’s easy-to-use statistical process control (SPC) automatically generates all the tools used by high-volume bakers today. “Dough Guardian can also be easily configured to send automatic emails of data, graphs and even alerts to supervisors of potential process variations before the final mix is complete,” Mr. Campbell said. “Bakers can then easily adjust mix times or ingredients as needed. Final product variations can be compared using the time-stamped data from each mix so the root cause can be found if it originated in the mixer.”
The Peerless Group, Sidney, OH, offers a highly sophisticated integrated mixer control system, Dough Quality Control (DQC), to help bakers improve product quality and consistency, according to Sherri Swabb, the company’s business development manager. “The system monitors dough temperature and consistency from batch to batch, measuring and displaying the instantaneous mix cycle energy curve along with a target energy curve as the dough batch is mixed,” she explained. DQC’s warning system also notifies operators when conditions exceed the customer’s defined upper and lower curve limits.
CMC America’s Batch Quality Control (BQC) systems assist with automating cycles on its horizontal mixers. BQC monitors power input as well as dough temperatures and alerts bakers if these are out of spec, so they can compensate for changes.
Reducing the cooling load on the mixing bowl represents the biggest advantage to mixing dough at slower speeds, Mr. Morabito said. “We have mixers that actually eliminated ice altogether and cut way back on glycol flow and usage,” he said. This approach affords twofold savings of energy. First, the mixers operate slower, using fewer amps to perform the same mixing action, and second, the dough requires far less cooling.
Reducing mix times even by a couple of minutes per batch can result in significant savings. “Depending on the price of energy per kilowatt-hour, a bakery could save $40,000 to $50,000 a year in electricity,” Mr. Fay said.
Many people in the industry mistakenly believe that dough character qualities are the exclusive result of formulation, Mr. Fay said. However, he observed, the type and speed of the agitators applied to doughs give different cell structure and aeration characteristics. “No matter what type of dough you making, the aeration characteristics that you impart to the dough are important and are a factor of the mechanical design of the mixer,” Mr. Fay said. “These can either increase or decrease mix times. We want our mixers to efficiently and quickly as possible get a dough to the right character, and then get it out of the mixer so that we can start the next cycle.”
CMC America’s most recent design changes to its horizontal mixers help bakers save energy as well as labor and operating costs, he said.
Labor figures into adding ingredients and helping discharge doughs, thus eliminating workers at the mixer is difficult, according to Mr. Bartsch. “There are options available that help to overcome the need for human intervention such as tilt options, including overtilt and programmable jog and discharge cycles,” he said. “Custom frames also improve automation of discharge. Purchasing a frame that allows proper discharge tilt can decrease the amount of human intervention needed.”
Mr. Campbell said that the easy automation of 140° overtilt mixer discharge systems into pumps or chunkers translates to labor savings and process consistency. It is possible now to implement a fully automatic system for sponge preparation, fermentation, final mixing, pumping, conveying, dividing rounding, moulding and panning from AMF for bread and/or buns with all of the process variables monitored from one SPC station and only one operator, he added.
DESIGNED FOR CLEANLINESS.
Sanitary design continues to be a major focus for all bakery equipment, and horizontal mixers certainly fit this trend.
Sanitary design represents the most critical current issue for horizontal mixers, according to Mr. Fay. “We must design systems in a way that saves operating, maintenance and sanitation costs,” he said. “You should be investing in a mixer that is the most versatile and the most cost-effective on long-term, indirect expense issues such as labor, sanitation, maintenance and utilities. That is what we have worked hard to do with our product line, and I know we are not alone with this issue.”
Improving seal designs and eliminating harborage areas are just a few of the things manufacturers have done to improve the cleanability of their machines. Mr. Morabito also claimed sanitary design was top of mind for Topos when developing its new horizontal mixers, and to that end, it constructs them of 100% stainless steel. “We don’t use any mild steel in fabrication,” he said. “Where a lot of other manufacturers have a mild steel base or a mild steel superstructure that is wrapped in stainless, we are 100% stainless steel.”
To improve sanitation and maintenance of its horizontal mixers, Peerless now offers new rotary shaft seals that eliminate the daily tasks of disassembly, cleaning and reinstalling seal shafts, according to Ms. Swabb. Low flow air pressure keeps ingredients out of the seal, preventing bearing failure or shaft damage caused by migrating abrasives.
Shaffer also developed positive-pressure bowl seals that have significantly reduced or virtually eliminated flour leaking from the mixing bowl during mix cycles, according to Mr. Bartsch.
Since introducing its horizontal mixer a couple years ago, Topos redesigned the drive line and how it compensates for deflection, according to Mr. Morbito. “We improved on that drive shaft and how the intermediate shaft is designed,” he said. “It now allows more deflection for greater longevity of the equipment.”
Topos, which builds new and rebuilds used bakery equipment at factories in the US and Europe, decided to start manufacturing new mixers after deciding there was still room for another manufacturer in this arena. After years of remanufacturing virtually every brand and type of horizontal mixer, Mr. Morabito said, the company used what it believed were the best proven features and technologies to develop its horizontal mixers.