Sifting: Sift Away
October 01, 2009
by Shane Whitaker
Unless you ask to specifically see the sifters, you most likely will not encounter them in most bakeries. Sifters are generally tucked away in rooms between the silos and the mixers. Nevertheless, sifters serve an important quality control function in bakeries by removing foreign materials, impurities and agglomerated product from dry powdered ingredients.
Sifters increase expectations for quality control and food safety, said Bob Ricklefs, vice-president of sales, Great Western Manufacturing, Leavenworth, KS. In addition, he cited recalls, employee safety, reduced manpower and employee turnover as factors that have led to improved sifter designs.
Great Western has noticed an increased demand for sifters to handle receipt of raw materials at the plant. “It appears that some strategic vendors have shared in the expense and/or operation of the sifting equipment applied on receiving systems,” Mr. Ricklefs said.
The top trend regarding this critical quality control step is to increase quality while reducing costs, according to Henry Alamazad, president of Kason Corp., Millburn, NJ. “To this end, processors are purchasing ingredients in larger bulk volumes, automating production, reducing waste, containing dust and taking measures to prevent material contamination problems,” he added.
Bakeries want low cost, reliable methods of improving quality by sifting flour, sugar, salt, cornmeal, powdered milk and eggs and other bulk ingredients, according to Mr. Alamzad. Kason sifters are available in numerous sizes and configurations and have satisfied the entire range of applications in the baking and snack industry, with capacities ranging from small batches to in excess of 40 tons per hour on a continuous basis, he said.
Bakeries more often are sifting all materials, according to William Kearns, vice-president of engineering, The Fred D. Pfening Co., Columbus, OH. This includes bagged ingredients that previously were not sifted at all. Processors are more concerned about adhering to codes that mandate 30 mesh for flour, if it will pass 30 mesh, using the finest screen possible, if it will not, he said. “We also see more instances of local authorities, usually health departments, enforcing these codes,” Mr. Kearns added.
More minor ingredient systems are incorporating sifting, and with the greater demand for whole-grain products, sifters are being used on wide-ranging materials, according to Mr. Ricklefs.
“With the current decline in the economy and acrossthe-board budget cuts, bakeries are now relying on one sifter to do the job of more,” said Randy Williams, c.e.o. of Sifter Parts and Service, Wesley Chapel, FL. “In some plants, sifters are being run at the highest capacity possible by using screens with larger than recommended mesh sizes. The CS-1 sifter is expandable, which can improve capacity without sacrificing food safety.”
Bakeries depend on sifting systems to provide accurate product sizing and elimination of foreign particles and contaminants to prevent costly losses of the ingredients and/or final product, he stated. “Recent recalls have led to greater awareness about food safety, thus prompting many bakeries to switch to magnetic stainless steel screens and metaldetectable nuts, bolts and cleaner balls and cubes,” Mr. Williams said. “Other bakeries are now using nylon mesh screens exclusively to eliminate the possibility of metal in their products.”
Mr. Ricklefs also noted that metal-detectable screen cleaners are requested more often nowadays. “In addition, and although we are often concerned with its use, customers are requesting magnetic stainless steel screens rather than a more fatigue-resistant synthetic screen,” he said.
Bakeries also want a reliable sifter with adequate capacity that offers easy sanitation and low maintenance, according to Mr. Williams. “Reliability, good capacity, easy sanitation and low maintenance equate to fewer man-hours, less down time and more effi cient production, which all lead to a stronger bottom line for the bakery,” he said.
Bakers can choose from a wide variety of sifters, including gyratory, centrifugal and vibratory. The aforementioned CS-1 is a gyratory sifter, and it has been manufactured for more than 60 years with relatively few changes, attesting to the sifter’s dependability, according to Mr. Williams. “The gentle gyratory motion keeps the product in constant contact with the screen surface to provide maximum capacity, while eliminating foreign contaminates from ¼ in. in size down to as fine as 400 mesh,” he explained. “The CS-1 was designed to require as little maintenance as possible, and with the addition of the new optional inspection portholes, it is possible to perform a full visual inspection of the entire screening surface without the need to disassemble the sifter.”
Great Western Tru-Blance sifters also feature a horizontal gyratory motion using standard motors and V-belts to turn two counterweights positioned on the left and right sides of the machine. “These weights straddle the machine’s center of gravity and counterbalance the mass of the rotating sifter housing,” Mr. Ricklefs observed. “This unique drive mechanism, invented by Great Western, ensures a smooth, balanced operation and minimizes stress to the structure.”
Great Western offers both in-line or gravity flow sifters that can sift hard wheat bread flour on a 30-mesh screen at rates from a few hundred pounds up to 1,200 lb per minute. The in-line sifter is by far most preferred by bakers and mix plants because of system simplification. “Gravity flow sifters are not designed to accept air flow that will influence the sifting action,” Mr. Ricklefs said. “When properly applied, many systems require two blowers along with associated filter receivers, airlocks, surge hoppers and dust control to enable the product to reach its destination.
“In contrast, in-line sifters are inserted directly into pneu- matic conveying systems,” he continued. “Eliminating the need to go from one conveying state to another and back again saves a great deal of extraneous equipment.” The initial system investment and installation costs are substantially lower for in-line systems, and the on-going operation, maintenance and sanitation expenses over the life of the system are reduced. In addition, he noted that the in-line concept does not require as much costly equipment after the sifter.
Pfening sifters also employ gravity flow and gyratory motion of the screens to achieve gentle, effi cient sifting action without using spinning blades or other means to move the product, according to Mr. Kearns. “This is in conformance with BISSC and other codes,” he noted. “Pfening sifters are capable of sifting most dry ingredients commonly used in the baking industry, including all types of flour, granulated sugar and starch. We offer three different sizes — the difference being in the screening area. The capacity of each machine varies widely by the type of product. We offer free product testing to determine the optimum screen mesh and capacity for our sifters.”
What sets Pfening sifters apart from others is the fully field-replaceable screens, which reduces maintenance time and costs, according to Mr. Kearns. The lightweight aluminum sifter decks are separate from the housing and do not require heavy lifting or special tools to remove or inspect, according to Mr. Kearns.
Great Western sifters feature sanitary 304 stainless steel construction on all contact surfaces and offer easily maintainable sieve frames with sanitary screen attachments. Its nest-together sieves enable the sifter to be opened quickly and completely for inspection, cleaning or maintenance, according to Mr. Ricklefs. “The sifters feature a unique pneumatic sieve clamping system,” he added. “The upper and lower components stay in the machine. Only the sieves are removed. The machine can be quickly, easily and completely opened in just minutes for inspection, cleaning or maintenance.”
The all-metal CS-1 from Sifter Parts is capable of providing two, three or four separations of any dry free-flowing product from ¼ in. in size down to as fine as 400 mesh. It is expandable and can provide from 10 up to 35 sq ft of screening area, all in a 4-ft-by-4-ft footprint simply by adding additional screen decks. The sifter has the capacity to screen up to 50,000 lb per hour of white flour on a 30 mesh screen, according to Mr. Williams.
The CS-1 has recently been upgraded to include optional screen inspection portholes on new screen decks, and worn decks can also be retrofitted with this modification when sent in for rebuild. In addition, to meet consumer demand, the company now offers standard and magnetic steelcore polyballs and cubes that can be detected in the event of a screen failure.
Sifter Parts also manufactures a new portable reclaim sifter that is handy for sifting small batches or reclaiming product normally lost through tailings or dusting overflow, he said. It sifts up to 600 lb per hour and operates sitting on top of a heavyduty plastic container or drum.
Kason manufactures circular vibratory and centrifugal screeners for baking and snack food ingredients, and each type offers a range of advantages depending on the size and nature of the application, according to Mr. Alamzad. These screeners are offered in gravity-fed and in-line pneumatic models for batch or continuous operation and in all-stainless steel construction.
Its Vibroscreen circular vibratory screeners use multiplane, inertial vibration to causes particles to pass through the screen or travel across the screen surface in controlled pathways. These systems range in diameter from 18 to 100 in. and are available with single to multiple decks, separating particles in one to five predetermined sizes ranging from 2 in. to 400 mesh (37 micron). “A wide range of models, including low-profile configurations, and specialized options satisfy a broad range of applications from the most simple to the most challenging, in capacities ranging from several pounds or kilograms to more than 30 metric tons per hour,” Mr. Alamzad said.
Material is fed into a inlet in Kason’s Centri-Sifter centrifugal sifters and redirected into the cylindrical sifting chamber by a feed screw. Rotating helical paddles in the chamber continuously propel the material against the screen, while the resultant centrifugal force on the particles accelerates the materials through the apertures. The paddles never make contact with the screen help to break up soft agglomerates, which makes it an ideal choice for continuous scalping of dry or moist materials that tend to ball or agglomerate. Oversized particles or trash are ejected via a discharge spout.
The company’s latest introduction is a twin centrifugal screener that sifts dry bulk materials and reduces soft agglomerates within a smaller footprint than two individual screeners. Cantilevered 3-bearing shafts allow quick removal of internal components from the shaft ends for quick washdowns, according to Mr. Alamzad.
So whether used only when products are delivered to processing or when materials arrive at the bakery, sifters and screeners play an integral role in food safety and assist the baker to produce high quality foods free of contaminants.