For the past 50 years, the basic design of donut fryers has largely remained the same. Build a large vat for heating oil and install a conveyor that flips the donuts and removes them from the fryer. What has changed about donut frying technology, however, is oil care.

“Frying technology is all about how to increase the life of shortening because that’s an expendable item and an expensive item,” said Roger Faw, president, Belshaw Adamatic Bakery Group, Auburn, WA. “The more we can do to enhance the shortening life, the better payback the bakery gets.”

Everything about donut frying contributes to damaging the quality of the oil, which, in turn, degrades donut quality. Heating the oil inefficiently breaks it down. Fines and particulates in the oil can speckle the product. Even oxygen deteriorates oil quality. Through filtration systems, new heating methods and equipment design, donut fryer manufacturers have placed the tools in bakers’ hands to take care of their oil and produce quality donuts. 

Filtering out floaters

Caring for the oil or shortening is a top priority for donut manufacturers. The oil is the heating medium through which donuts cook, and its quality directly affects the characteristics of the finished product. Keeping the oil clean and fresh is a good first step.

Whether frying cake or yeast-raised donuts, inevitably some particulates and fines are going to come off the batter into the oil. Too many of these floaters can cause problems in the finished product.

“As you build up fines, it directly affects your oil quality because all that material is starting to carbonize and react, and it makes maintaining a uniform and stable oil quality exceedingly difficult,” said Doug Kozenski, sales manager for processing systems, Heat and Control, Inc., Hayward, CA. “In our opinion, you need to filter and remove fines as quickly as possible.”

As particulates settle on the bottom of the fryer, a sediment removal conveyor pulls them to where they can be filtered out of the oil. Then, these continuous filtration systems return the clean oil back into the fryer, which saves bakers precious dollars on this hot commodity. Returning clean oil to the fryer can be delicate too. “That oil is added back to the fryer in a controlled manner because we don’t want to stir the oil up too much and create more fines and particulates that can cause dark spots or speckling of the product,” Mr. Kozenski said.

Constantly removing floaters lengthens the oil life and cuts down on how often the fryer needs to be cleaned. By removing them continuously, bakers can drastically reduce buildup on the fryer. The Libra fryer from Moline Machinery, LLC, Duluth, MN, comes with a sediment removal conveyor and continuous filtration system that drastically reduces sanitation downtime. “People who needed to clean twice a week, now may only have to empty their fryer maybe once a month or once every two weeks, so they get that much more uptime,” said David Moline, the company’s sales and marketing manager.

Filtration is so crucial to maintaining oil quality that when Belshaw Adamatic was developing its partnership with JBT FoodTech, Chicago, IL, to deliver large industrial donut fryers, JBT’s filtration system was a major selling point. “They have a filter system that is by far the best filtering system for shortening that I’ve ever seen, so we wanted to include that in our package,” Mr. Faw said.

Designed for oil care

Beyond adding a filtration system, certain design aspects of a fryer encourage long oil life. Cutting out oxygen degradation and improving oil turnover can all be addressed by simple design changes in the kettle.

Exposing the product or oil to oxygen can cause oil to break down. Traditionally, frying kettles for donut production have been open and exposed to the air with an area hood and exhaust above. Heat and Control brought the hood down to the fryer to create an enclosed unit. This minimizes the amount of oxygen that interacts with the oil.

While some frying kettle designs may be getting longer or wider, Belshaw Adamatic kettles are becoming shallower. This leads to faster oil turnover and fresher oil for better quality donuts. With its new shallow kettles, oil turnover happens at least once for every 8-hour shift. According to Mr. Faw, reducing the depth out of the kettle was the company’s biggest challenge in addressing oil life.

Moline Machinery also made its Libra kettle shallower because, according to Mr. Moline, turnover is critical to maintaining oil quality.

These seemingly simple changes can make a baker’s oil or shortening go further in donut production.

Heating efficiently

The most basic element to frying — heat — is also one of the most harmful to oil. Temperature control not only prevents thermal degradation of oil but also ensures a better finished product. Wild temperature swings and overheating both damage oil, so bakers need frying systems that maintain an even temperature.

Offering bakers greater control over the oil temperature spurred Moline Machinery to develop its Libra hybrid fryer. A variation of its original Libra electric kettle, the new fryer is a dual-fuel fryer using both gas and electricity to heat the oil. Gas cross burner tubes can heat up the vat of oil, while the electric element allows bakers to fine-tune the temperature with control not normally found in a gas fryer. “You’re able to do the heavy lifting with gas if you want to and the fine-tuning with the electric,” Mr. Moline said.

Dual heating also can optimize operational costs. The fryer can be adjusted to draw more of its heating capability from either natural gas or electric, depending on which energy source is less expensive.

While most donut fryers use direct heat, thermal fluid can provide a more uniform temperature throughout the fryer. Direct heat fires flames inside a series of tubes submersed in the oil that run the length of the frying kettle. This provides some challenges in temperature balance and uniformity.

Looking for a more efficient and uniform method to heat oil, Heat and Control developed a thermal fluid system about five years ago. The company’s U-tube design runs longitudinally in the fryer instead of across. Thermal fluid circulates throughout the tubes, heating the oil. According to Mr. Kozenski, there is no variance in temperature across the fryer width, which has become important as fryers have gotten wider throughout the years.

JBT also uses thermal fluid to heat the industrial fryers it builds with Belshaw Adamatic. Mr. Faw agreed that thermal fluid is a much healthier heating process for the oil and limits degradation.

In direct heat systems that Belshaw Adamatic uses for its smaller fryers, keeping the flame hot enough in the tube is also a challenge. The company recently transitioned all of its mid-level fryers to premix gas instead of atmospheric burners.

Premix gas offers more balance and control in the oxygen-to-gas ratio than atmospheric burners. This ensures the hottest flame stays hot. However, because of the efficiency and uniformity of JBT’s thermal fluid system on its larger fryers, Belshaw Adamatic is considering adapting its smaller fryers to that as well, Mr. Faw said.

With all these design advantages and systems in place to ensure oil quality and lengthen oil life, bakers still have do their part. Bakers have to keep the fryer clean and free of debris, either by implementing a continuous filtration system or batch filtering the oil at regular intervals. As Mr. Faw said, “You can provide all the tools to do that, but it’s up to the bakery to make sure it happens.”