Although flour sifting often occurs at the silo, bakers shouldn’t think about this technology in a vacuum. Commercial baking is a process for which sifting is just one part, so it’s important to understand how it plays into the whole process.
“Location and usage will depend on the ingredient and manufacturing process,” said Ken Johnson, president, Gemini/KB Systems. For example, if a process calls for minor ingredients that easily clump, he suggested that the KB centrifugal system be located right off the discharge.
Whether it’s at a hand-add station or part of a pneumatic system, sifting all depends on the operation, types of ingredients and needs of the baker.
“You need to look at where the material goes into the process,” said John Hunter, sales account manager, bakery and ingredient handling, Bühler, Inc. “If we need to put screening systems in and if we’ve got an automated system, when ingredients go into the tipping station or point of transfer to a receiver above the mixer, then we’ll want to have the sieve — and the magnet — at that point.”
There are times when minor ingredients are sifted before they’re stored in silos, but that doesn’t mean it’s the end of the exercise.
“If it’s sifted upon receipt, it could then be done again when the ingredient comes out of its use bin,” said Jeff Seeger, technical sales engineer, Great Western.
Bakers who pre-scale minors before storing them often benefit from offline sifting in the ingredient prep area, said Jason Stricker, director of sales and marketing, Shick Esteve. And when it comes to automation, bakers may choose to sift as ingredients are introduced into the system.
“For example, a bag dump with an integrated screener would allow you to measure ingredients without the extra step of sifting, but it would also allow protection when it comes time to transfer into the mixer,” he said.
In an automated system, the sifter’s location can affect process efficiency.
“For pneumatically conveyed ingredients, inline sifting is most efficient where the product velocity is slowest, namely where it first enters the conveying line,” said Zach Turner, sales manager, AZO. “If you put a sifter 100 ft down the line, all that product has gained a ton of speed, and you’re going to force ingredients through the screens rather than actually performing the sifting task. When you have the most efficient sifting, you take full advantage of your machine, rather than sneaking product past the safeguards because it’s traveling too fast.”
Speed and efficiency come into play for Pfening as well.
“In a pressure system, ingredients will generally flow through just fine, but your system will need to be sized at a little slower feed rate to properly get through the sifter,” said Darren Adams, vice-president, engineering, the Fred D. Pfening Co.
In this case, Pfening typically calculates that time into the design of its ingredient handling systems.
“It’s not something someone feels or notices in the process, but it’s taken into account during the design phase,” he said.
Sifting doesn’t always have to occur at the beginning of the overall process, and a bakery doesn’t need to have an automated ingredient handling system to take advantage of this tool. In fact, Mr. Hunter said many bakers choose to sift minors at their specific points of entry, such as near the weigh scale.
Other bakers look point-by-point.
“Some customers ask us to sift wherever the ingredients are introduced because they want to make sure nothing goes into the process unsifted,” said Lisa Arato, regional sales engineer, Zeppelin Systems.
Some formulas call for a lot of minor ingredients that require bulk bags at multiple locations, and the size and type of the ingredient often determines how many machines are needed on the line.
“Different ingredients have different particle sizes, so you may need a dedicated sifter for specific ingredients,” she added. “Or, you could use a common sifter if the ingredients are of similar particle sizes.”
Ms. Arato also cautioned that sifting should occur before the weigh scale; otherwise the measurements could be thrown off.
Screen size, sturdiness
A bakery doesn’t have to house a behemoth operation to benefit from sifting. In fact, Great Western offers smaller systems to suit those companies.
“We have a smaller arrangement for people who don’t need 30,000 lbs per hour but maybe only need 50 to 60 lbs,” Mr. Seeger explained. “Maybe a baker is putting corn bran back into a product to raise the fiber content or other ingredients to boost nutritional value. These smaller units will fit more in line with those types of capacities.”
It wasn’t too many years ago that sifting was sifting, no matter what ingredient or product.
“As long as you had a screen, it was fine,” Mr. Hunter recalled.
But in today’s world of technological advances, customization is the status quo. And that carries all the way to sifter screens. Having multiple screen options can sometimes be an alternative to having multiple sifters on the line.
“You might make a product that has a grain in it, and you could sieve your sugar with a 1.5- or 2-mm screen, but the grains can’t get through a 1.5-mm screen,” Mr. Hunter suggested. “For the grains, you may need to have a large screen, but you want it to be as small as it can be. So, when you think about multiple points, it might actually be the same point, but in order to screen ingredients appropriately, you need different sieve sizes.”
When customizing its equipment, Bühler can design a sifter with very fine mesh sizes; in fact, the screen is often the basis for the custom design.
“A customer needs to first look at the sieve size; then you can think about the construction,” Mr. Hunter said. “‘What’s the screen made out of, and how do I make sure it doesn’t cause a problem?’ In centrifugal systems, they would be made of magnetic stainless steel because those screens will reduce the risk of them breaking.”
For larger bakery applications, Bühler typically avoids nylon screens because of the risk they could break.
“That’s why we choose sturdy materials like stainless steel,” Mr. Hunter said. “That really is a robust screen.”
Nylon screens usually provide a lesser throughput, Mr. Adams said, because the mesh is coarser to provide that tensile strength. Ultimately, there’s a screen to match any throughput requirement.
“For an easy upgrade, some people will switch to stainless steel temporarily until they can get their new sifters onsite and get the system ramped up,” he said.
While Zeppelin still offers polyester screens for its rotary sifters, the company also recently changed over to wedge wire screens for its strength and detectability.
“With the wedge wire, you can use a magnet in the process, so if there’s a screen breakage, you can detect it,” Ms. Arato said.
Mr. Adams said the screen is the sifter’s most vital organ.
“What we now know about sifters is that screens are the most important part,” he said. “I’ll even go a step further to say we built reinforced screens because higher-pressure systems can wear differently with additional force, so we have some material reinforcement in some of our screens, as well.”
This article is an excerpt from the February 2019 issue of Baking & Snack. To read the entire feature on sifting, click here.