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The Science of Crispy Snacks
February 1, 2008

Do you know what makes a cheese puff puffy?

Sajid Alavi does. He’s an engineer and assistant professor with Kansas State University’s department of grain science and industry. He teaches and researches about a technology called extrusion processing that is used to make a variety of foods such as pasta, cheese puffs, breakfast cereals and pet foods. His recent research has involved running bran-enriched flour through an extruder to see if it could be used to make healthier versions of tortillas and cookies which taste as good as the original.
Prof. Alavi said extruders are machines that work by pushing dough through a narrow barrel using a series of turning screws.
“We can control the speed of the screws,” he said. “By controlling that, we can control the process. We can make a pasta, a snack or a cereal.”

The friction of the screws produces heat that subsequently raises the temperature in whatever dough is being pushed through the extruder. The extruder barrel can also be heated for foods that require a higher temperature. Prof. Alavi said pastas are created with a low-temperature process, while snacks like cheese puffs get their crunch from higher temperatures.

“When you’re heating the dough and there’s a lot of water in there, the water turns to steam,” Prof. Alavi said. “It pops like popcorn and puffs up. When the dough expands, it gives you the desired crunch.”

The type of die used when the dough is being pushed out of the extrusion extruder determines the shape of the product, such as that “O” shape for a popular breakfast cereal, Prof. Alavi said. The extrusion lab at K-State has die in about 50 different shapes, including the letters of the alphabet and even K-State’s own Powercat logo. He also was involved in a project that made a medicated goose feed in the shape of kernels of corn.

“You can process almost any grain-based material into a final cooked or formed product of a desired shape, size and mouth-feel,” he said.

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