Advances in industrial frying

quality, according to Kane.

“The oil turnover rate is the time (hours) taken to replace all the oil in the fryer and its systems.”

Filtration systems are very important in maintaining oil quality and are either active, in which negative components created by frying are chemically removed; or passive – when fines and particulars are physically removed by mechanical action.

“This is the most commonly used method for potato crisp frying.”

In a full volume oil filtration system, the oil filter is selected based on particle size; particle buoyancy; the volume of particles; the system oil volume; and the filtration cycle rate.

“In most of our systems, we try to put the whole volume of oil at least once every minute through physical filtration,” Kane said. “Fines that are not removed from the fryer can be a major cause of oil degradation.”

Fryer heating

There are essentially two classes of heating systems to heat a fryer.

Direct heating where the heating system is installed inside the fryer.

“This is used less and less within the industry as immersion tubes in the fryer pan below the cooking zone are more difficult to control,” Kane said.

In indirect heating, the heating source is external to the fryer, utilising different systems to heat the oil.

Gas-fired external heat exchangers use gas combustion to heat the oil. Steam external heat exchangers have a shell & tube heat exchanger using steam as the heating method. Thermal fluid external heat exchangers use an externally-heated thermal fluid to heat the oil.

Market trends

Key trends of today include a focus on health, energy efficiency, sustainability, pollution control, low carbon emissions and energy savings, Kane said.

“All efforts and money are being driven towards how to have carbon neutral energy costs.”

Kane said up to 90% of carbon produced in a plant could be from energy used to heat oil but deep fryers could create positive change with the right equipment and control of their process environment. “Raw potato, for example, is 77-80% moisture.” This was a lot of moisture and, consequently, steam that could be captured to heat oil, thereby reducing energy usage.

“A 3,000kg potato crisp fryer, for example, needs up to 6MW of energy. If we generate this using electricity, the costs can be four times more than using gas.”

A system that compressed steam and created energy to heat thermal fluid could reduce carbon, but at a cost. As an example, a carbon neutral heating system could cost five to six times more than the current standard system.

New technology

Multi-stage frying offers cooking at varying temperatures for different products, using recovered energy, according to Kane. It utilises two, three or more fryers in tandem, each with its own heating source (see Figure 1, right).

Advantages include the ability to achieve a final moisture content using a separate fryer where a low finishing temperature of less than 1200C is used to inhibit the formation of acrylamide.

“Considerable temperature profile flexibility provides the ability to produce hard-bite style chips and regular chips on a single system.”

Air frying at home is another growing trend, popular because it uses less oil and heats food evenly and quickly.

On an industrial scale, industrial frying equipment supplier Heat & Control offers an air fry system (AFS), where oil is sprayed on a product before pressurised cooking in an impingement oven.

“Air fryers create food products that have a reduced oil content compared to submersion-fried products,” Kane said. The systems could be sized to meet production requirements, and worked with standard batter and breading application systems. The AFS system was not suitable for potato crisps as too much surface area was needed for oil spraying, but would work with coated and non-coated products such as chicken breasts, strips, nuggets and other boneless chicken pieces. It could also work for:

• Breaded seafood such as popcorn shrimp

• Breaded vegetables such as onion rings

• Non-breaded products such as baked taquitos and egg rolls

“Although, industrial air-fried products do not taste the same as their traditional fried counterparts, they do match or exceed what is being produced by home air frying systems that are becoming more prevalent in kitchens around the world,” Kane said. “The consumer can now have an off-the-shelf healthy alternative they can purchase at their local market.”

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