Hot Oil Filtration Improves Profitability of Fried Food Operation

Drum filtering for hot oil

Hot oil filtration is important in any food processing area that uses fryer oil to create the finished product, such as convenience foods like chicken and French fries, snack foods like tortilla chips, and elements of ready-made meals. When oil is effectively filtered from a commercial deep fryer, it improves the profitability of the food processing and the quality of the food to the consumer.

By using a hot oil filter, the fryer oil does not need to be replaced as often, reducing the expense of purchasing new oil while improving the fried food’s profitability. The filtered oil is also darker than fresh oil and, when used for frying, provides a more appealing end product.

The quality of a commercially fried food product can depend on many things, but most importantly, the quality of the oil it is fried in. That balance of moisture, flavor, and crunch is the experience consumers enjoy and that commercial fried food processors try to achieve. Besides providing heat to cook in, the fryer oil becomes part of the end product, as much as 40% in the case of potato chips. With good oil, food tastes better, is healthier, has an improved shelf life, and the oil lasts longer.

Evaluating Oil Quality: Crumbs, Color, and Free Fatty Acids

One of the challenges of long term oil use is the chance that chemical reactions cause changes in the oil, which can affect food quality. Things that might be left in the oil include batter, breading, or even proteins. These solids, crumbs, and fines continue to cook, and they can turn into burnt and denatured organics, known to affect taste.

An oil filtration system can remove these solids and more while integrating smoothly into the industrial frying operation, which often includes the frying unit, a heat exchanger to heat the frying oil, circulation pump, tanks for dirty and clean oil, a control system, and the oil filtration equipment. Fresh oil is continually added to the system, as there is some inherent drag-out of oil in the product leaving the fryer and integrated into the food product.

Of the three key ways that oil quality is evaluated – the crumbs, the color, and the level of free fatty acids (FFAs) – the color and crumbs are more often addressed by common filtration processes. However, these solutions do not often address a crucial issue: the level of FFAs in the oil, a key indicator of the overall oil quality and contributor to the oil’s useful life.

Reducing Solids Through Filtration

Conventional filtration uses gravity, pressure, or a vacuum to create a driving force necessary for the slurry (oil and solids) to pass through different kinds of medium, such as woven wire, cellulose filter papers, glass fiber filters, or granular material.

Other, less common mechanical methods include membrane filters that rely on media with much smaller pores and temperature limited operations.

Many of these systems require high maintenance and significant periods of down time. Filter paper systems, in particular, require frequent down time as the paper gets saturated with contaminants and needs to be changed, sometimes multiple times a day. They also have capacity issues, as ultrafines can limit filtration throughput.

WesTech’s Vacuum Drum Filtration Removes Solids and FFAs

WesTech has decades of experience in filtration, successful for the food processing industry.

That expertise has helped the company adapt its outstanding water filtration technology to hot oil filtration in the food processing industry. For example, a customer with a large poultry processing plant in the South used our Vacuum Drum Filter technology to apply precoat filtration to its hot oil frying filtration needs.

The customer targeted removal of suspended solids and reduction of FFAs to a level of 0.5 – 1.5 ppm. If the FFAs are higher than 1.5 ppm, then a scorched taste and smell become apparent. It is difficult to achieve an FFA less than .5 ppm. The customer was considering a filter paper technology but recognized it could not meet its FFA requirement, so the customer contracted with WesTech for a Vacuum Drum Filter instead.

Vacuum Drum Filter Panel Installation

The Vacuum Drum Filter has a porous, screened drum cylinder, ranging in size from 18 inches to more than 8 feet in diameter. The outside surface is precoated with an FFA absorbent and a pearlite diatomaceous earth media. The hot oil is sucked by the vacuum through the precoat bed on the drum’s surface to the inside drum piping and sent on its way to the clean oil tank.

There are two processes of filtration as the oil passes through the filtration bed on the drum. First, the suspended solids are captured on the outside of the drum. Next, the clean oil passes through the absorbent portion of the drum coating, where the soluble FFAs are absorbed. When the drum turns, it passes an advancing knife that cuts off the particulate solids and a very thin layer of the filter media, part of a sacrificial filtration media bed. This allows a fresh filter surface to be re-immersed in the dirty oil as the drum continues to rotate.

Illustration of vacuum drum filter in operation

The filter is simple to install in the production line, and it easily adapts to filtering high temperature oil. WesTech adapted the technology, usually used for wastewater, for use with hot oil, adding high temperature equipment safeguards, ensuring the critical oil quality, and allowing for redundant controls.

The WesTech filter was installed in a new plant where the owner wanted to incorporate a filtration system to keep from having to discard spent, high FFA oil. Choosing WesTech’s vacuum drum filtration for the plant introduced a one-step operation to clean the oil, both removing the FFAs and addressing the oil’s color and crumbs. Using this system, the company could recycle its oil nearly indefinitely, with make-up required only for the product drag-out, thus improving the economic value stream.


Commercial food processors who produce fried food can sell used fryer oil and recover a little money from their outlay cost that way. However, it is more economical to sell drag out oil with the high-value fried food product. Companies need solutions that allow effective reuse of the oil so it can continue to be used for frying.

WesTech’s Vacuum Drum Filter is an option that includes both mechanical and chemical processes with demonstrated success in the hot oil filtration market. At this Southern U.S. processing plant, the FFA level was tested on a sample a few months after installation, and the results showed the oil in the clean range, a win for processors and consumers.

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