Quick Mixing with Vertical Mixers
Oct. 1, 2011
by Shane Whitaker
Bakers who use spiral mixers generally make smaller batches, which can lead to a more labor-intensive process. However, automated carousel and robot mixing systems eliminate the manual handling disadvantages normally associated with vertical spiral mixers, and they can mix batches quicker to meet the needs of lines that are used to larger batches.
Also, by mixing smaller batches more frequently, spiral mixers can provide fresher dough to the production line, and that often allows the makeup equipment to work more smoothly, according to Stephen Bloom, vice-president, Allied Bakery Equipment, Santa Fe Springs, CA, the North American distributor and manufacturer for Sancassiano SpA, Roddi d’Alba, Italy.
Most doughs can run in a makeup line for 10 to 18 minutes without affecting product quality or production performance, according to Mark Rosenberg, founder and CEO, Gemini Bakery Equipment Co., Philadelphia, PA. However, some doughs and processing equipment have issues after exceeding as little as 10 to 12 minutes. “The dough becomes bucky and harder to handle due to dough type and processing requirements,” he said.
Gemini recently installed a spiral system at an Italian bakery that had ongoing problems with dough at the end of each mix cycle. The bakery would cycle each dough batch every 18 minutes, and toward the end of processing each batch, the bakery saw major increases in out-of-spec product because of dough stickage and product shape. The dual-tool WP Spiral Power Mixers reduced batch times to less than 12 minutes, and this dramatically reduced the number of cripples, according
to Mr. Rosenberg.
Some bakers may wonder if spiral mixers are robust enough to handle their doughs. Planetary-style vertical mixers have long been used by bakers, but when the vertical spiral mixers developed in Europe began crossing the Atlantic, questions arose. According to Mr. Bloom, European manufacturers did not understand the strength of American flour, thus the machines were not built to withstand the stress of mixing American doughs. “This, of course, has been addressed by now, at least by the serious manufacturers,” he said. “Vertical mixers are, in fact, appropriate for virtually any dough.”
Whether it’s Danish, bread, bun or donut dough, spiral mixers do a good job because they are versatile, easy-to-use and sturdy, according to Louis (Sonny) Avanzino, Western region sales manager, Belshaw-Adamatic Bakery Group, Auburn, WA.
Vertical mixers also provide flexibility and allow bakers to tinker with the process, according to Mikaël Roussière, sales director, VMI, Montaigu, France, with US offices in Atlanta, GA. Bakers can use a variety of mixing tools and scraping devices, change resting time and employ a sponge-and-dough process all with the same mixers, he said.
“The adjustable speed of the mixing bowl and/or tool gives more flexibility to work the dough very gently,” Mr. Roussière said.
For a couple of reasons, spiral mixers have played an important role in the growth of artisan bread in the US, according to Mr. Bloom. First, the mixers excel at developing highly hydrated doughs that are generally used in artisan bread processing. “Second, artisan bread is, in general, a product with European roots, and so the people trained to make artisan bread have learned from bakers who were using vertical mixers and, therefore, are comfortable with that solution,”
Mr. Bloom said.
Artisan breads such as baguettes, ciabatta and focaccia are made from soft, highly hydrated doughs that require gentle mixing action, according to Mr. Roussière. Gluten must be stretched carefully to obtain the final product volume, open cell structure and light, creamy color associated with artisan breads. “Reducing the speed of the mixing tool and using the speed of the bowl allow the elongation of the gluten in a very soft manner,” he added.
Several years ago, Sancassiano introduced the Hydra mixer, which Mr. Bloom referred to as “a completely different way of mixing.” It features two vertical bars that rotate within the bowl and meet in the center. The mixing action stretches and compresses the dough in a manner that closely mimics the way a baker would mix dough by hand, he said.
As a result, the mixer creates much less friction and binds more water. Less friction means much lower temperature rise during mixing than that of traditional spiral mixers. Because hardly any energy is wasted as heat, Hydra requires much less energy to mix dough, Mr. Bloom said.
Hydra’s mixing action allows the gluten web to develop more completely and absorb more water. Thus, Mr. Bloom said, bakers can “sell more water” by making higher-
hydration doughs. Also, making bread with more moisture extends its shelf life.
During the past three years, Sancassiano invested heavily in R&D to develop its Genesi series of mixers. Using computer analysis and scientific tests, the equipment manufacturer updated the construction principles used to build its mixers, according to Mr. Bloom. For example, the company measured and recorded stresses to the mixer during dough development and then analyzed those results to redesign mixer frames to be 30% lighter yet 60% more rigid than in the past.
Gemini’s Power Mixer bottom-discharge system comes standard with a 2-speed motor, but optional infinite variable-speed mixing tools and bowl are available. The mixer comes standard with computerized controls. Stainless steel dual-spiral mixing tools help the mixer produce dough with shorter mixing times, increasing hourly output. In fact, Power Mixer can output six 529-lb dough batchers per hour, for a total hourly capacity of 3,000 to 6,000 lb.
Sancassiano’s Kryos mixer combines the advantages of the Hydra and horizontal mixing, according to Mr. Bloom. “The Kryos is essentially Hydra technology but with a static, oval bowl,” Mr. Bloom said. “If the mix is not too highly hydrated, we found that in an oval bowl the dough would circulate between the tools on its own without bowl rotation.”
The static bowl helps solve what is often seen as one of the main disadvantages of vertical mixing: the inability to jacket and cool a rotating bowl. When required, vertical mixers will generally use ice or carbon dioxide for cooling dough, but the Kryos can be jacketed to achieve the temperatures needed for frozen doughs or in extremely hot environments, Mr. Bloom observed.
A bottom-discharge option allows mounting the Kryos mixer on mezzanines or platforms to release doughs directly into existing trough systems. “If a plant is already built around the presence of horizontal mixers, this feature eliminates the issue of having to reconfigure infrastructure to accept the new technology,” Mr. Bloom said.
Vertical mixers require perfectly round bowls and a breaker bar in the middle of the bowl to avoid dead spots, Mr. Roussière said. Also, the mixing tool’s shape must provide a good combination of stretching, shearing and aerating, he added.
Consistent bowl construction is essential to mixing performance. “Because of the way the bowls have typically been made, most manufacturers have had difficulty guaranteeing a tight tolerance in bowl roundness and inside dimensions, bowl to bowl,” Mr. Bloom said. “The implication of this is a lack of repeatability or consistent dough quality from batch to batch because the mixing tool could be closer to the side on one bowl than another and produce different mixing results in development and in dough temperature using the same mix time and tool speed.”
Sancassiano manufactures its own bowls, using a new technique that allows accuracy five to 30 times more precise, depending on which aspect the company talks about, than previous bowls, Mr. Bloom said. “This leads to predictable and repeatably consistent dough temperature rise and batch-to-batch mixing times,” he noted.
AUTOMATION AND SANITATION.
Certain design features enable full automation of vertical mixing systems. For instance, when working with highly hydrated or stickier doughs, vertical mixing bowls can be automatically scraped on a bowl elevator, Mr. Bloom said. Also, scrap dough and ingredients can be automatically integrated into doughs into a carousel or robotic vertical mixing system.
Sanitation is another essential. “In a modern bakery, mixer design must accommodate easy and thorough cleaning,” Mr. Bloom said.
The latest advances in vertical mixers from VMI have concerned construction and materials. “The market is demanding low maintenance equipment that is easy to clean,” Mr. Roussière said.
VMI Expert mixers feature tubular structures and smooth outer casings. They are made using hydrophobic materials without any retention areas, which simplifies maintenance and keeps the mixer clean longer, he noted.
Bakeries that may have dismissed vertical mixers in the past, thinking their operations were too large, may want to take new look at them. The ability to supply fresher doughs more frequently to the divider merits consideration.