French fries are beloved around the world, but the cooking method that gives them their signature crispiness also allows them to absorb significant amounts of oil.
Now researchers at the University of Illinois Urbana-Champaign say a different approach to frying could reduce how much oil ends up inside the final product.
In two new studies published in the Journal of Food Science and Current Research in Food Science, scientists examined how combining conventional frying with microwave heating might lower oil absorption while maintaining the taste and texture people expect from fries.
The research helps explain a basic challenge of frying: why foods soak up oil in the first place.
During the early stages of frying, potato tissue is filled with water. As the fries cook, that water begins to evaporate, leaving behind tiny pores where oil can enter.
Principal investigator Pawan Singh Takhar, a professor of food engineering at the University of Illinois, described the process with a simple analogy.
“Think about a straw in a drink. If you push air into the straw, it creates positive pressure and any liquid will be pushed out,” Takhar said. “But if you suck on the straw, the liquid moves upward. Now imagine food materials have lots of tiny straws. When there is positive pressure, the oil stays out. But if there is negative pressure, the oil starts moving in.”
According to the researchers, much of the frying process occurs under negative pressure, which encourages oil to move into the food.
Microwave heating may help counteract that effect.
Unlike conventional frying, which heats food from the outside inward, microwaves heat water molecules throughout the food. This can produce vapor more quickly and increase internal pressure inside the potato.
“The microwaves oscillate water molecules, causing more vapor formation and thus shifting the pressure profile towards the positive side. The higher pressure in microwaves helps reduce oil penetration,” Takhar said.
In laboratory experiments, the team prepared potato strips that were peeled, rinsed, blanched and salted before frying them in soybean oil heated to 180 degrees Celsius. The researchers monitored changes in temperature, pressure, moisture, texture and oil content during the cooking process.
They compared conventional frying with microwave-assisted frying using two microwave frequencies similar to those used in consumer microwave ovens and industrial equipment.
Overall, microwave frying produced faster moisture loss, shorter cooking times and lower oil absorption.
But there was a tradeoff. When microwave heating was used alone, the fries tended to become soggy rather than crisp.
To address that problem, the researchers proposed combining microwave heating with conventional frying in the same system. Conventional heat would maintain the crispy exterior, while microwave heating could reduce oil uptake inside the food.
The team also used mathematical modeling to simulate how factors such as pressure, temperature, moisture and oil movement interact during frying. These models allow scientists to explore how different conditions influence food quality during cooking.
While the research focused on French fries, the findings could apply to other fried foods as well.
The scientists suggest that industrial fryers used by food manufacturers could potentially be modified to include microwave generators, which they describe as relatively inexpensive and widely available.
Such changes could allow producers to reduce oil absorption while maintaining the texture consumers expect from fried foods.
The two studies offer new insight into the physics of frying and how food engineers may be able to adjust cooking methods to produce lower-oil fried foods without sacrificing taste or texture.
The research was funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture.