Humanity has been making flour out of seeds since ancient times. Archaeological evidence for making bread by crushing seeds into flour has been found in what is now Jordan, a site used by hunter-gatherers over 14,000 years ago. Ancient Mesoamerican cultures used corn flour in their cuisine since ancient times, while the Romans were the first to use cone mills for grinding seeds into flour. Rye flour is still prevalent throughout northern and central Europe, and the French are famous for their light and fluffy baguettes made from wheat flour. Yet the process of making flour changed in 1786 with the development of the first mechanized flour mill in London, which was powered via a steam engine.

Today, rotary sifters are an integral piece of equipment used in the mass production of various flours. Capable of processing free-flowing and fine materials at a high rate of speed, rotary sifters are part of a cost-effective mechanized solution to process all types of flour. Rotary sifters efficiently and effectively sift and scalp material to remove foreign substances and oversized particles during the flour production process. Further, they’re capable of handling materials containing significant amounts of moisture. In fact, modern flour-making methods depend on rotary sifters to mass-produce flour that’s used to feed the world.

Equipment Used for Processing Wheat Into Flour

Flour can be made from just about any plant containing edible starch, including acorns, barley, buckwheat, corn, hazelnuts, lima beans, millet, oats, peanuts, potatoes, quinoa, rice, rye, soybeans, and wheat. However, most flours are made from grains, and wheat is by far the most common constituent in flour production. Wheat grains can be milled into different types of wheat flour. White flour uses only the seeds’ endosperm. Whole Wheat flour uses every part of the grain, which includes bran, endosperm, and wheat germ. All these flours are produced similarly, but for simplicity’s sake, we’ll concentrate on how grains, particularly wheat, are made into flour using rotary sifters.

Rotary sifters are typically used for scalping away foreign particles and those that don’t meet specifications during large-scale flour production. They’re used for ensuring quality prior to the blending process, commonly placed at the point of use - in industrial bakeries, for example - to screen incoming flour. Rotary sifters are part of a larger system that includes equipment for grinding, sifting, and purifying the seed and flour, along with systems that remove dust. This equipment will often include pneumatic mills, impact mills, blenders, bran finishers, purifiers, and rotary sifters, or some combination of these machines. 

Importance of Rotary Sifters in Flour Milling

Rotary sifters – also known as rotary sieves, rotary screeners, or centrifugal sifters – work on the principle of centrifugal force. They screen material by using paddles to impart this centrifugal force, which accelerates particles across the screen surface. Rotary sifters help classify and filter flour particles and remove impurities. Their ability to screen fine powders with extreme precision makes them a very useful tool in any flour production system. Rotary sifters are primarily composed of a motor, mesh screen, inlet for feeding, discharge hoppers, access doors for inspection/ maintenance, and support base.

Benefits of rotary sifters in flour production include:

  • Highly efficient
  • Quiet operation
  • Runs continuously without problem
  • Screens are easy to change, clean, and maintain
  • Suitable for a wide variety of materials

Rotary sifters are perfect for producing flour and are useful for other products within the food and agricultural industries, along with construction, medical, recycling, and other sectors.

How Rotary Sifters Work

Rotary sifters use a centrifugal motion to create movement horizontally, vertically, and in an inclined position. This delivers flour particles to the rotary sifter’s screen surface, where it’s classified. Material then either moves through the screen and onto the next stage in the process or returns to be reground. 

Flour milling operations will utilize differing systems for breaking down and reducing the wheat. This requires classifying the grain once ground with plansifters. During the sifting process, flour particles are separated based on size, with the smaller ones falling through the screen’s holes. As such, rotary sifters play an integral role in the efficiency and output of a flour mill, along with the quality of the flour it produces.

This sifting process depends on the size of the openings on the screen, size of the area allocated to separate flour particles, material load on the rotary sifter, and how quickly particles are moving in relation to the screen’s surface, If these factors aren’t optimal, inconsistency in particle size could result, which would then affect the quality and yield of the flour produced. Rotary sifters also prevent bran contamination and irregular granulation.

Maintaining Regulatory Compliance

In addition to the quality of the flour, rotary sifters help food processing plants that use the flour comply with all necessary rules, regulations, and legislation, including the Food Safety Modernization Act (FSMA). The most comprehensive food safety law passed in over seven decades, FSMA helps ensure the safety of the US food supply, focusing on preventing contamination. As noted earlier, a key role that rotary sifters play in flour manufacturing involves removing contaminants. This additionally involves compliance with Hazard Analysis and Critical Control Points (HACCP), which has become recognized internationally as a system that can be utilized to identify and manage risks associated with food safety.

When used appropriately, HACCP handles food safety concerns for customers, the public, and regulatory agencies. It also shows that there’s a well-managed food safety program in place. The system addresses food safety by seeking to control physical, chemical, and biological dangers resulting from flour production and any issues regarding consumption, distribution, handling, and manufacturing. Through maintaining HACCP compliance, today’s flour manufacturers and grain processors can certify the quality and safety of their products.

Prater Rotary Sifters

Prater Industries manufactures a range of rotary sifters, including our trademarked Rota-Sieve®. Designed for sieving operations like flour production, our rotary sifters help remove foreign substances like rocks, plastics, strings, or insects. Its lightweight, simple design makes cleaning, inspections, and maintenance easier, ensuring compliance with both FMSA and HACCP.

Prater rotary sifters offer numerous other advantages.  Prater’s design offers higher throughput per unit of screen area, meaning more capacity in a smaller, more compact footprint. Prater sifters also offer greater efficiency, up to 99.99%, meaning a higher percentage of good flour is recovered and used in the process.  For example, this means that for a throughput of 20,000 pounds of flour per hour with a machine with a waste stream of 1 percent, that's 100 pounds of useable flour wasted every hour. With a price average of 50 cents per hour, this translates to $1200 per day of wasted material for a continuously running operation or $438,000 annually!  

To learn more about Prater’s Rota-Sieve® or other rotary sifters, we invite you to contact our expert team today.