Mixers: Developing Dough
April 1, 2010
by Shane Whitaker
Mixing, the first processing step in making yeast-raised baked foods such as bread and rolls, is the act of combining ingredients into a homogeneous mass. The mixer initiates the interactions between water, flour, salt, fats, sweeteners, yeast and a host of other diverse components, and the development of the dough plays a major role in making a quality loaf of bread.
Bakeries can use more than a half dozen methods for creating doughs, including straight dough, sponge-and-dough, liquid sponge and no-time dough, and they can use continuous or batch systems. Numerous innovations in the design, efficiency and flexibility of mixing equipment have been made in the past year. Many of these and more will be on display at this year’s Baking Expo.
Normal operating procedures are seldom seen in bakeries, according to Matt Zielsdorf, vice-president, sales and marketing for The Peerless Group, Sidney, OH. Accordingly, the equipment manufacturer has designed its latest systems to account for anomalies that occur in operations. “When we sell a 2,000-lb mixer to mix 1,800-lb batches of bread dough, we realize that in the real world the customer might run an occasional 900- to 1,000-lb batch of a different bread type, thus putting undue stress on the mixer,” he said. “To meet the ever-changing needs of bakers, we redesigned our already strong mixing bowls to be even stronger, using our patented z-profile designed channels.”
Finite element analysis demonstrated that the new bowl decreased bowl stress/deflection by 42%, and computational fluid dynamics analysis resulted in a 40% reduction in pressure drop of coolant and a 60% reduction in flow recirculation in the jacketed bowl, according to Mr. Zielsdorf. These new features allow Peerless’ mixers to assist bakers in creating better-developed and colder doughs, he added.
Peerless manufactures triple roller bar mixers with capacities ranging from 300 to 3,200 lb. What makes these mixers unique, according to Mr. Zielsdorf, are its patented bowl designs, sanitary designs including all-new shaft seals and a variety of cooling options such the patented refrigerated triple roller bar agitator.
Horizontal mixers from Oshikiri Corp. of America, Philadelphia, PA, feature a redesigned framework to minimize distortion and deflection during mixing, according to Tim McCalip, national sales manager. Also, it made design changes so that its mixers have better seals on the doors, thoroughly locking in ingredients and minimizing leakage for a more hygienic operation, he added.
AMF Bakery Systems, Richmond, VA, is starting to make its horizontal agitator bar mixers in smaller sizes, including 400- and 600-lb capacities, and the reason for this is twofold, according to Larry Gore, vice-president of sales and marketing, AMF. First, it meets the needs of bakers in emerging markets such as China and the Middle East, which are starting to make more Westernized products. Second, bakers want fresher doughs rather than have large batches sit in the hopper for a longer time. “Even in the sponge-and-dough situation, they will use a single sponge mixer and generally two final mixers to produce fresher doughs,” he said.
In addition to stationary bowl mixers, AMF also offers tilt and offset tilt bowl mixers to allow for a totally automated mixing system. Its offset tilt bowl mixer tips 140° toward the front, dropping the finished dough in a dough distribution system, whether it be an AMF dough pump or dough chunker that automatically transfers the dough via a conveyor belt to the makeup equipment without human involvement, according to Mr. Gore. “Bakeries want to reduce ‘hairnets’ in the mixing area because there is no added value,” he said. “You must have a certain level of production to justify automation, but most high-speed bakeries are going for total automation instead of semiautomatic or manual operations.”
To automate the mixing process, Kaak Group North America, Lithia Springs, GA, offers bottom-discharge spiral mixers from Diosna. These mixers are available in sizes up to 1,000 kg (2,200 lb) and can feature single or double spirals or the Wendel tool for mixing, according to Bob Marraccini, vice-president, Kaak Group North America.
Topos Mondial, Pottstown, PA, offers new horizontal mixers with 90, 110 and 140° tilting options. The overtilt design features heavy-duty hydraulic actuators.
Topos mixers include the J.H. Day bowl design that is proven for fast and efficient mixing of yeast-raised doughs, according to Louis Doleac, sales manager of new equipment. It also has adjustable roller bar positioning with the improved 4-position UHMW bushing block. “This allows for maximum mixing performance for your particular dough mixing needs,” he added.
MIXING BY ENERGY.
Another trend with horizontal mixers involves the drive systems and how they tie into the electronics, according to Mr. Gore. Whereas horizontal mixers have traditionally used 2-speed motors, today most bakeries opt for a single-speed motor with an AC inverter, which allows for a variable-speed drive system. “This gives bakeries the capability to run at an infinite number of speeds to optimize the mixing profile for the dough they are making,” he said. “It also allows them to maximize energy efficiency because they only need to run the mixer at an optimum preset RPM instead of either slow or fast. The RPM of the agitator affects the amount of energy it consumes.”
AMF unites the drive system and electronics using its Dough Guardian system, which analyzes the energy consumption necessary for each mixing profile, according to Mr. Gore. Mixing generally has been performed for a set period of time, but with the Dough Guardian system, bakeries will be mixing by energy, using energy profiles of the mixer to tell when a dough is done. When a bakery has variability in raw materials such as a flour batch that is either weaker or stronger in protein, it may want to increase or decrease the mix time so it can produce the same product time after time, according to Mr. Gore. However, he pointed out that it is difficult to have a floor operator who is used to running a 12-minute dough to run it for 11.5 minutes.
The Dough Guardian system monitors the energy input of the agitator bar and, using wattage graphs, can determine when mixing is completed. One of the most important advantages of the system is product consistency, he said. Dough Guardian gives bakers scientific data to analyze performance. It also allows them to analyze energy usage in other mixes, so they can download a history to a companywide system for analysis.
CMC America Corp., Joliet, IL, offers triple roller bar mixers with Batch Quality Control (BQC) systems for automating mixing cycles. BQC accurately monitors the power input, according to Ed Fay, director of sales, CMC. It is unique in the fact that it monitors power input every second on all three cables that power the mixer. “We make a fingerprint, and you see the power go up and down and can understand fully what is happening with the dough,” he said.
In addition, to monitoring the power, BQC also plots the temperature of the dough throughout the batch, and if the dough exceeds its target temperature, it will alert the baker so he or she can bring the dough back into conformance. “Most importantly in our systems is the interest and ability to make a mixer reduce and optimize the speed of dough development,” Mr. Fay added. “There are many challenges in getting a dough mixed correctly and doing it in the least amount of time.”
Accordingly, the company has applied for patents on its agitator, bowl configuration and jacket designs. Oftentimes, people at look triple roller bar mixers and think they are all the same, he said. However, Mr. Fay pointed out that there are differences and that the relationship between the agitator and bowl shape of CMC mixers help to better aerate doughs. “We want to increase turbulence of flour and water in the first 30 seconds of mixing so we can get the highest possible hydration into the flour,” he said. “We get to the ‘pickup’ stage in about 30 seconds with our mixers, but then you have to transition into a gentle folding action so you don’t rip the gluten matrix being developed.”
Mr. Fay said that most industrial bakers are embracing the benefits of variable frequency drives because of the versatility and performance they provide, as well as their benefits for energy efficiency.
Mr. McCalip also observed the trend to use inverters on motors. In addition, Oshikiri is installing more direct drives on its horizontal mixers and moving away from belts and gears within the drive system. With a direct drive system, there are fewer parts to wear out, he added.
Shaffer Manufacturing, a Bundy Baking Solution company, Urbana, OH, uses direct drives on its open-frame horizontal triple roller bar mixers because they offer reduced maintenance and quieter operation, according to the company. Its enclosed-frame mixer features either single- or double-end chain or belt drive options. Both mixers are available with either dual-speed or variable-frequency drive motors for agitator operations.
Shaffer also developed a new exclusive bowl design that provides reduced mix times, allowing for greater throughput in the bakery, according to Terry Bartsch, vice-president, sales, Shaffer.
Many features on WP Group mixers help bakeries improve consistency, according to Michael Eggebrecht, bakery consultant for the WP Bakery Group, which includes Kemper Bakery Systems, Shelton, CT. For example, he noted that program controls make production more simple, and in conjunction with a frequency inverter, it gives the baker ultimate control of the mixing process, by varying the speed of the bowl and the spiral rotation. “This knowledge can be used by all operators even when the head baker is not there,” he added.
Bakers are demanding greater dough consistency in the form of colder doughs and a desire for greater throughput in the bakery, according to Mr. Bartsch. “To meet the demand for colder doughs, we enhanced dough refrigeration options in our roller bar mixer,” he said. “We have redesigned our bowl jacket cooling to provide better coolant turbulence for greater heat transfer, and we offer refrigerated agitator bars for an additional 3 to 5°F cooling compared with standard jacket cooling.”
AMF is working to optimize the cooling capabilities on its mixers, thus it redesigned the cooling jackets to take advantage of the performance of glycol or chilled water. “A lot of jackets designed for Freon were not optimal for glycol or chilled water, so we redesigned them to ensure we get maximum cooling from these coolants,” Mr. Gore explained.
In addition to jackets, the mixer manufacturer also offers bowl-end, breaker bar and agitator cooling as options. “We have the capability to cool the entire interior of the mixer,” he said.
Besides the cooling jackets, the most common options are bowl-end cooling followed by chilling the breaker bar. Cooling the agitator is the most costly and also the least requested of the options, according to Mr. Gore.
Shaffer’s open-frame mixer design offers easier sanitation along with simplified maintenance procedures for some components, according to Mr. Bartsch. Its triple roller bar mixers also include maintenance- and lube-free bowl mounting bearings and agitator shaft bearings.
Oshikiri has improved sanitation of the butterfly area where flour is delivered into the mixer. The valve is now wiped clean as the bowl tilts back up, whereas previously the dead area could not be cleaned effectively until the mixer was shut down, according to Mr. McCalip.
Topos offers both butterfly and slide gates at the flour inlet, as well as a sanitary design for easy cleaning with full access to all surfaces, according to Mr. Doleac.
Because hygiene is a growing concern for bakeries, the Titan double-tool spiral mixer from the WP Bakery Group has been developed in two versions. “The standard version with computer controls and automated lubrication, and the professional version with a washdown capability and automatic monitoring of motors, bearings, etc.,” Mr. Eggebrecht said.
Since mixing is the first process in creating yeast-raised baked foods, it is an extremely critical step in determining how the final product is going to turn out. If a bakery is inconsistent with the doughs it produces, it’s going to have a hard time making reliable product again and again.