When making yeast-raised donuts, each part of the process builds on the steps before it.

“Everything is important,” said David Moline, vice-president of sales and marketing, Moline Machinery. “If there’s a problem upstream in mixing or makeup, it’s very difficult to correct that downstream. Equipment can respond, but it should be noted that, especially with yeast dough, having a consistent process in delivering dough to the system is arguably as important as how the system itself is operated.”

Delivering consistent dough depends on creating a sheet without imparting tension. Then it all comes down to temperature control, whether it’s in proofing or frying or as donuts cool down for icing. With so much integration between systems, controls become crucial.

Consistently making up

Donut quality is determined early in the process, and makeup keeps that quality going down the line. For yeast-raised donuts, that means keeping tension out of the dough sheet.

“If the dough sheeting process is not optimized, therefore allowing for more tension in the dough, the result will be inconsistent product shape and quality,” said Nick Magistrelli, vice-president of sales, Rademaker USA.

WP Bakery Group USA

The company uses its DSS or LSS front ends to create the original dough band without any stress. An automatic dough flow program maintains the sheet with minimal tension as it moves through reduction stations. Rademaker selects the proper reduction components for the dough and integrates automatic controls to minimize opportunities for operator errors.

Consistent donut size also starts at the makeup section of a donut line, though it’s finalized in the proofer. WP Bakery Group’s Kemper donut line features a divider/rounder system that accurately portions and rounds dough pieces for consistent sizes. Flat-pressing stations then evenly press donuts for a round flat dough piece. Before entering the proofer, donut holes are finally stamped out of the dough pieces. The entire system is designed for consistent and accurate donut weights and minimum re-worked dough.

Automation and control

Yeast-raised dough is always developing throughout the production process until fried, which halts the yeast activity. To maintain consistency in the donuts’ size and quality — and avoid human errors — automatic controls monitor production and maintain constant conditions throughout the process.

“Due to the full automation and having a constant process, the products are equal in shape, size and color,” said Ken Weekes, international sales manager and product manager, roll lines, WP Kemper.

This is particularly important at the proofer and fryer, which are linked on high-capacity donut systems. When a change is made in one system, it’s going to affect the other.

“The ratio of proofing time to frying time becomes fixed,” Mr. Moline said. “Having extremely precise heat and humidity control in your proofer is critical.”

Dual-zoned proofers grant operators some of that control in large systems. Each zone can be set up for different temperatures, humidity levels and proofing time to meet the product’s needs.

“We’re able to offer accurate and flexible climate control with dual zone proofers that have completely independent heat and humidity control,” Mr. Moline said.

Topos Mondial’s dual-zone donut proofers can be powered with steam or electric heat and atomized water for the humidity.

“We have very close temperature sensing in the box to ensure we maintain the proper temperature by zone, and humidity control with proper circulation is very key in a yeast-raised donut proof box,” said Damian Morabito, president, Topos Mondial.

The proof boxes also circulate the air using variable speed rather than fixed. This also aids operators in controlling temperatures in both zones.

Temperature and humidity control are critical not only for a consistent proof but also for accommodating fryer adjustments. As fry temperatures or times change, so will the proof times, temperatures and humidity levels. An automated system makes those adjustments.

“If there’s an adjustment that has to be made like frying or proofing time, the entire system reacts in time,” Mr. Moline said. “For example, if the frying time is adjusted to be a bit shorter, the system is going to run a little bit faster, so everything from the very beginning of the dough former is going to speed up accordingly.”

Moline Machinery does this efficiently by supplying a single donut system. The sheeting, proofing and frying are all on the same PLC rather than integrating three different controllers. There are operator interfaces at each step; however, they are all working on the same system.


“In a yeast-raised donut system, we don’t view the sheeting, proofing and frying as three separate pieces,” Mr. Moline explained. “We view that as one single system, so that’s how we treat it.”

WP Bakery Group’s Kemper donut systems also allow operators to view all parameters on several displays throughout the line. Any necessary adjustments can only be approved by authorized personnel, and then the rest of the system automatically accommodates.

“Our systems are largely autonomous with only the need for operator surveillance, filling flour dusters and tool changes when the product is changed,” Mr. Weekes said. “This reduces the human error factor dramatically.”

Belshaw fryers are also recipe-controlled, so operators don’t have to remember every setting.

“An operator taps a product image on a touchscreen, the frying program changes, and the rest of the donut line synchronizes speeds immediately,” said Mike Baxter, product information and marketing coordinator, Belshaw.

PLC controls on Heat and Control’s fryers can interface with upstream or downstream equipment to make sure production is running in sync.

“Signals can be provided for proper transfer timing and communicate with host systems to provide real-time process data for data collection and other uses,” said Doug Kozenski, sales manager, processing, Heat and Control.

Temperature sensors on Topos fryers keep track of the surface temperature of the oil — where donuts will actually cook — and PID-type controllers will use that information to maintain the oil temperature.

“They’re self-adjusting controls,” Mr. Morabito said. “All the operator has to do is set it and forget it.”

The fryer controls also communicate with the proofer to automatically adjust to any changes.

Heat and Control also relies on automated controls to maintain oil level and temperature.

“Proper and effective temperature control is a key component of maintaining oil quality,” Mr. Kozenski said.

Fully modulated burners keep cooking oil temperature within 1˚F of the set temperature.

Oil level is maintained within 1/8 inch of the set point by routinely adding small amounts of oil.

“This ensures an adequate amount of oil in the fryer for proper transfers and processing and avoids temperature variances that can affect product consistency,” he said.

Protecting the environment

The proofer and fryer, two of the most critical points in donut production, are all about providing the perfect environment for donuts to accomplish a just-right proof and the perfect fry.

“If a dough is under-proofed or over-proofed, that has a lot of effects that you’ll see in frying,” Mr. Moline explained.

These can include a poor donut shape or excess oil absorption.

WP Bakery Group’s Kemper final proofer is not only automatically controlled but also built with 3-inch insulated walls to ensure constant temperature and humidity. The company’s fryer also is insulated to minimize heat loss.


At the fryer, incorrect oil temperatures can cause a breakdown in oil or result in a less than acceptable product quality. While automatic temperature monitoring and controls can help the fryer reach the proper temperature and maintain it, even if the fryer is open, the bakery’s environment can counteract all those automatic measures.

“You have environmental concerns like drafts and airflow in the plant makeup air,” Mr. Morabito said.

If an air-conditioning duct is blowing directly onto the fryer, it will not only cool off the oil’s surface where frying happens but also blow smoke throughout the bakery instead of pulling it through the fryer’s hood.

Heat and Control features a fully enclosed hood over the frying kettle, which seals the fryer pan.

“This closed environment greatly reduces the infiltration of air into the fryer and significantly reduces the oxidation rate of the oil,” Mr. Kozenski said.

From one process to the next

Because yeast-raised donut dough is ever-changing before it hits the fryer, transfers can be a point of contention.

“Take the proofer-to-fryer transition as an example,” Mr. Baxter said. “You want it to be as seamless as possible, but the donuts may have a tendency to stick to the proofer basket instead of dropping off cleanly.”

Without a clean transfer, yeast-raised donuts can lose some of their shape and excess dusting flour can enter the fryer, causing more fines. Belshaw developed its Active Release system to assist in a clean transfer into the fryer from the proofer, and its proofer baskets are coated in Teflon, reducing the amount of dusting flour needed.

Topos’ transfer between proofer and fryer features an automatic aligning system.

“The product will present into the fryer flight perfectly each time, so we eliminate waste,” Mr. Morabito said.

This prevents donuts from getting stuck on a flight bar or entering the turner incorrectly.

The turn can also be a tenuous transition. This is the moment the donut is flipped to fry the other side and is dependent on the donut’s size. Topos’ uses a gentle turner that allows operators to adjust to the height and width of the product and prevent splashing.

This article is an excerpt from the November 2019 issue of Baking & Snack. To read the entire feature on donuts, click here.