Mixing with precision
Nov. 1, 2013
by Shane Whitaker
Like an artist mixing colors before painting a masterpiece, bakers must properly combine dry and liquid ingredients to create dough that will yield quality finished products. Mixing represents the crucial first processing step in converting raw materials into breads, buns, rolls, sweet goods and more. There is no turning back once mixing begins. The process’ physical and chemical actions play a vital role in determining the final quality of the products made from the dough. That’s where process control comes in.
PLCs and computer systems connected to mixers play an integral role in giving bakers control over this process. These systems can track ingredients usage so bakers have the necessary documentation for pending food safety regulations. They can ensure the dough reaches its optimum development at the right time to maintain a production schedule.
Dough mixing is about consistency in the development process, and that’s how computerized controls give bakers big advantages. “Finishing a mix too early or too late can cost a bakery in quality or efficiency,” said Bruce Campbell, executive product manager, dough processing technology, AMF Bakery Systems, Richmond, VA. “So there is a huge responsibility for PLCs and software monitoring to ensure the dough is right, at the right time.”
Because knowledge of the process before, during and after final mixing is critical, AMF developed Dough Guardian, a statistical process control (SPC) tool for data analysis, quality control and troubleshooting. The system tracks the critical variables in the mixing process such as flour and water temperatures, sponge temperatures, energy input, glycol temperatures, pressure in and out of the bowl, and final dough temperature. These data are kept in a batch file, which can be presented graphically in SPC charts.
“For example, a histogram of final dough temperatures for the third shift can be automatically displayed for the production manager when he comes in at 8 in the morning,” Mr. Campbell noted. “With one glance, he can tell if his mixing process was under control the previous night.”
Such recipe management systems make the operator’s job much easier. For example, the Dough Guardian system displays in real time the conditions of the mix. “This offers the operator insight into what is going on inside the bowl without having to open it up and look at the dough,” Mr. Campbell explained.
Computer-controlled systems are critical, according to Jim Warren, director of Exact Mixing, Reading Bakery Systems, Robesonia, PA. Flow meters connected to the closed-loop control system ensure liquid ingredients are accurately delivered to the mixer and properly coordinated with the dry materials. Each ingredient stream is monitored in real time to confirm that the formula is correct. In effect, the computer-controlled mixer guarantees the correct formula prior to mixing.
Computers detect any deviation from the target prior to the forming stage. “The mixing process is carefully monitored, and the operator is alerted if any issues arise,” Mr. Warren added.
The Codos continuous mixing and kneading system from Zeppelin Systems USA, Odessa, FL, includes a complete dosing unit for the blending and homogenization of dry ingredients as well as liquids. This results in gentle handling, energy savings, constant dough temperatures and increased line efficiencies, according to Stephen Marquardt, the company’s food sales director.
These mixing systems can be used for a single line or flexible production lines making a variety of products. A well-functioning continuous mixing system relies on the preparation, handling and continuous feeding of raw materials — the focus on Zeppelin’s business for many years, he noted.
PLCs play an integral role in automating the Advanced Batch Mixer series, a line of high-speed, high-intensity systems from Advanced Food Systems (AFS), Columbus, OH, according to Denny Vincent, president. The control systems manage the scaling of all dry and liquid ingredients. The mixers’ controls also deliver chilled water at exactly the right temperature to achieve the desired final dough temperature, he noted, because dough is not in the bowl long enough to be chilled by a jacket.
Integration with the sponge, fermentation and pumping systems is critical to making sure operators kick out dough at the correct time, temperature and development level. AMF offers single-point controls to integrate the entire mixing and makeup system to run fresh dough accurately, according to Mr. Campbell.
If you prefer a mix-to-energy approach for assuring proper dough development, consider a control system capable of governing that operational aspect. For example, AFS’s high-speed mixers offer this function. “By using a PLC, you can monitor the energy that goes into the mix, thereby ensuring that the dough has reached an optimum level of development,” Mr. Vincent said.
Getting a clear view of how a dough comes together — measured by energy input, agitator speed, ingredient consumption or other variable — is the function of a central operator interface terminal (OIT). In the case of the Exact Mixing system, the entire process is controlled by just such a terminal. “The operator can view the details of the mixing process at any time at the OIT,” Mr. Warren said. “Statistical data can be reviewed in table or graphical form to show the efficiency of the mixing process over any period of time.”
Such data is useful to managers as well as operators. “This information can be transmitted to quality control offices, manager offices or to offsite devices so everyone is always up to date,” Mr. Warren observed. Having a history of the mixing process also is important for traceability.
The touchscreen operator interfaces with PLCs on Shaffer Mixers’ triple-roller-bar horizontal mixers feature push buttons with universal labels for frequently used functions. The Urbana, OH-based company, which is part of Bundy Baking Solutions, offers enclosed, hybrid and open-frame roller bar mixers, and all three styles include the interface in a Watershed operator panel enclosure.
Controls also improve security. Password-protected PLCs and recipe control systems on mixers from Topos Mondial Corp., Pottstown, PA, prevent operators from changing the formulas; only the supervisors have that access, noted Damian Morabito, the company’s president.
Highly hydrated dough
Because force and friction can heat dough during the mixing process, cooling via glycol, CO2 or ice is often required. A different approach was described by Ken Schwenger, president of Bakery Concepts International, Mechanicsburg, PA, which represents Rapidojet mixers in the US. This mixing system, which injects high-pressure liquids into dry materials as they fall, relies on incoming water temperatures to control the dough-out temperature.
“The normal mixing process consumes a tremendous amount of energy and labor,” he noted. The Rapidojet, however, consumes a low 1.5 kilowatt-hour (KWh) per ton of dough, he explained and pointed out that this technology repeatedly produces consistent and homogeneous dough at measurably higher hydration levels.
High-absorption doughs characterize today’s popular artisan-style breads and rolls. For baked foods not covered by a federal Standard of Identity, elevating the water content of the dough also minimizes bowl costs while maximizing shelf life. This happens, Mr. Schwenger explained, because the Rapidojet process yields homogeneous doughs with little, if any free water. “Therefore, the baker can add more water to the product to gain the same dough characteristics as from normal mixers,” he said.
Likewise, high-speed, high-intensity mixing, a feature of the AFS systems, can increase the amount of water incorporated into the dough and cut overall mixing time to two to three minutes for full dough development. These units employ both a center-mounted high-speed agitator, operating at 600 to 1,200 rpm, and a side scraper tool turning in the opposite direction at about 24 rpm.
The slower-speed scraper circulates dough back into the mixing tools in order to reduce mix times and improve hydration. “If the mixer just had high-speed tools and no scraper, it would not be able to mix as quickly or as thoroughly as it does,” Mr. Vincent said.
Drive motors for more conventional mixers are changing, too. By equipping the Topos Mondial horizontal roller-bar mixer with a variable-frequency drive, the equipment manufacturer added a dynamic brake on the agitator drive system. This design change prevents the agitator from coasting — a potential safety concern. “This brake stops the agitator immediately after the operator removes their hand from the jog controls,” Mr. Morabito said.
Topos Mondial recently launched an open-frame horizontal roller bar mixer. The company focused its efforts on designing a heavy-duty open-frame machine with a D-shaped bowl to assist with dough development. Mr. Morabito said bakeries can slow down the agitator speeds to better knead the dough while also reducing overall processing times.
The process of blending ingredients to make dough represents a key first step in making quality baked foods, and by taking control of this process using computers and PLCs, bakeries can better manage the final quality of their products.