Different doughs work best at certain temperatures. Therefore, bakers attempt to control the dough’s temperature during mixing, which is a function of adding energy to dough that, in turn, generates heat.
In fact, just adding water to flour liberates heat of hydration — 6.5 Btu per lb of flour. Yes, heat is also generated by the friction of ingredients in contact with one another and the bowl surfaces. However, as Terry Bartsch, vice-president of sales, Shaffer Mixers, a Bundy Baking Solutions company, noted, heat also comes from warm ingredients and ambient temperatures. The mechanical input of the mixer’s motor and agitators also contribute to the dough’s heat level.
Desired final dough temperatures depend on the product and process. Generally, the acceptable final temperature for most bread and bun dough ranges between 75 to 80°F. With less developed products such as pizza and frozen dough, bakers aim for exit temperatures in the lower 70s or even cooler. Cookie and pie bakers need even lower temperatures. In fact, Denny Vincent, president of Advanced Food Systems, Columbus, OH, noted some processors want cookie doughs as low as 45°F.
“On the other extreme, high-intensity mixing and developers on bun doughs can kick out a dough near 90°F that will process fine,” said Bruce Campbell, vice-president, dough processing technologies, AMF Bakery Systems, Richmond, VA, “Flour tortilla dough is often sent to the divider around 90°F to make the press operation easier.”
Dough-out temperatures play an important role in the dough’s quality and machinability. “The key is to find a dough temperature that makes the proper dough for the finished product and allows the dough to be machined properly,” said Jim Warren, director of Exact mixing at Reading Bakery Systems, Robesonia, PA.
Bakers want dough at the target temperatures to control yeast activity. “When dough is too hot, it becomes ‘bucky,’ or too gassy, and it will not go through traditional divider/rounders,” said Ken Schwenger, president of Bakery Concepts International, Mechanicsburg, PA. “If the dough is too cold, it will be too stiff to flow properly through the makeup machines, resulting in poor shape and scale weight.”
Fortunately for processors, as Mr. Campbell pointed out, “If the mixer’s cooling system is properly designed and in automatic mode, the dough should always come out right on target temperature.”
Cooling options abound
Bakers employ a variety of methods to control dough temperatures. They can introduce chilled water, flour and other ingredients to the mixer. Glycol cooling jackets help regulate dough temperatures inside the mixer, as do refrigerated breaker bars, bowl ends and agitators. Bakers also can add ice to their mixers or use snow horns, which blast liquid carbon dioxide (CO2) into a mixer to lower dough temperatures.
Shaffer generally proposes bowl jacket and agitator cooling for this purpose. “These two technologies have the greatest dough cooling capability,” said Mr. Bartsch, who spoke about “Controlling Dough Temperatures” during a breakout session at the American Society of Baking’s BakingTech earlier this year. “The jacket accounts for most of the cooling; however, adding a refrigerated agitator has been shown to decrease final dough temperature by 5 to 6 F°.
“The refrigerated agitator has had a big impact on dough cooling,” he continued. “In the past, bakers also used bowl end and breaker bar cooling; however, those technologies only offer an additional 0.5 to 1 F° decrease in dough temperature each.”
In addition, Shaffer’s refrigeration monitoring systems measure the glycol flow and mixer inlet and outlet temperatures and send this information to the mixer control panel. “This can help bakers fine-tune their refrigeration system to get the desired final dough temperature and allow them to monitor these parameters to prevent undesirable final dough temperatures,” Mr. Bartsch said.
AMF offers glycol cooling jackets as well as refrigerated breaker bars, bowl ends and agitators on all its mixers. The company’s Cooling Calculator takes all of the projected inputs and provides a model of the Btus, or energy, that will be generated during the mixing process. “We then compare that to the cooling circuit capacity and make sure there is enough heat transfer capacity to dissipate all this mixing energy,” Mr. Campbell said. “Once this equation is balanced, you can be sure you will kick out doughs that are at the desired temperature.”
Designing sponge-and-dough or straight-dough systems with extra capacity can help ensure consistent temperatures. “By using multiple final mixers with extra capacity and predicting when the dough will be needed at the dividers, the final mix can wait until the exact time needed to start mixing the dough,” he explained. “This means at the end of the mix, the dough will have to be immediately kicked out. There is no wait time in the mixer where the temperature can change.”
If left in a chilled mixer for too much time after mixing, dough can become too cold, resulting in less ovenspring unless the proof time is adjusted. “It will impact makeup adjustments and create irregularity in the process, reducing product consistency, especially in a facility where multiple final mixers are being used,” Mr. Campbell said.
Configured for less heat
Although virtually all 3-roller-bar mixers from Topos Mondial Corp., Pottstown, PA, come with cooling jackets, Damian Morabito, the company’s president, noted, the mixers often run without the use of the bowl jacket. “If the dough is being properly kneaded and not ‘mixed,’ then it will not get too warm in the first place,” he said.
Too much emphasis has been placed on trying to make the bowl and agitator colder instead of designing the bowl and agitator in a way to knead the dough properly and not get the dough too hot, Mr. Morabito said.
“Spiral dough mixers have been, and continue to be, used for many years to mix all types of yeast-raised dough,” he observed. “They do not have any cooling jackets and rarely do the formulas require ice to keep the dough cold ... just chilled water. This goes to prove that you can get proper kneading without getting the dough too hot. When a 3-roller-bar horizontal mixer bowl and agitator are properly configured to work together and when the mixing rpm is proper for the absorption of dough that you are trying to mix, you will knead the dough and not mix it.”
This way, bakers have successfully cut mixing time using Topos’ mixers, according to Mr. Morabito. For example, the Topos mixer reduced mix times for a popular fast-food restaurant bun by about half. The mixer requires 1½ to 2 minutes in low speed and 5½ minutes in high-speed to achieve a fully developed dough at or under 78°F.
“We accomplish this mixing at slower speeds than normal and while using little or no bowl jacket cooling and at a much lower horsepower and amp draw,” he added.
Additional opportunities to reduce mix time and energy exist. For example, AMF demonstrated that its Y-T agitator can shave the energy needed for mixing by more than 10%. “One recent major installation on a North American bread line resulted in 1 minute reduced high-speed mix time and improvement in bread quality to the point that the production supervisor said, ‘We are mixing the best dough I have ever seen on this line in 20 years.’ ” Mr. Campbell recalled.
While bakeries may want to decrease mix times, they do not want to reduce development of the dough. To get the final desired baked characteristics of a dough, bakers typically cannot cut mix times or development using traditional mixers, according to Mr. Vincent.
However, high-speed mixers such as Advanced Food’s ABM 1000 can prune mixing time by 50 to 60% and still achieve the desired development, he said. In fact, mixing times are usually less than 2½ minutes, with complete cycle times for loading ingredients, mixing and automatic discharge of less than 5 minutes. Mixing chamber thermometers monitor dough temperatures in all the company’s high-speed mixers that typically bind up 5 to 10% additional water for higher absorption doughs.
Control with continuous mixers
Continuous mixing systems provide three opportunities to control exit dough temperatures, according to Mr. Warren. First, continuous systems require less energy for mixing than most traditional mixers. Because ingredients are added at the same time instead of separately, continuous mixers eliminate the need to pre-blend all the ingredients. “This typically reduces the required energy by 20%,” he observed.
Second, continuous systems increase the surface area per pound of dough mixed for more efficient cooling. Cooling jackets are much more effective because the dough touches the chilled wall more often.
Third, the mixer reduces the cross-sectional area of dough mass. “Because the dough is produced in a cylinder, the core can be cooled more efficiently,” he said. “In other words, thin pieces are easier to cool than thick.”
Downstream processing can sometimes be changed to accommodate temperatures that are not on spec; however, as Mr. Warren noted, “This generally leads to sacrifices in product quality.”
The Codos kneader from Zeppelin Systems USA, Inc., Odessa, FL, is a 2-stage continuous mixing process that stretches the gluten structure without shearing or cutting, according to Stephen Marquardt, the company’s North and South American sales manager. “We control the complete process from raw material handling and conditioning until jacketed cooling,” he added.
Bakers can achieve desired dough temperatures without using CO2 or ice using the Codos system, which also requires less energy. “The Codos process reduces the energy demand by a minimum of 30% compared with batch mixing operations,” Mr. Marquardt said.
For the best results, bakeries need mixers that ensure consistent and specific dough temperatures time after time.