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Engineering professor devises cutting-edge way to cut cheese better

Xiaochun Li and HongSeok Choi

Xiaochun Li, assistant professor of mechanical engineering, left, and HongSeok Choi, research assistant, use a cold laser to cut slices of American cheese into computer-generated shapes. (large image)

Slices of American cheese cut into computer-generated shapes by a
                        cold laser.

Lasers do everything these days — from removing tattoos to playing music on compact discs. Now, in the great dairy state of Wisconsin, lasers have been harnessed to an entirely new purpose: slicing cheese.

Xiaochun Li, a University of Wisconsin-Madison mechanical engineering professor and laser expert, along with graduate student Hongseok Choi, has become the first to adapt a so-called "cold laser machining" technique, primarily used in laser eye surgery, to the task of cutting cheddar. Not just a cheesy idea, Li, contends that the advance holds real promise as a clean, precise and cost-effective way to cut cheese commercially, especially into very thin slices.

"The fast-food industry wants cheese that is still nicely shaped, but is cut very thin so that customers consume less fat," says Li, who began the project at the request of a Wisconsin manufacturer of cheese-processing equipment. "But when you cut cheese thinner and thinner, mechanical systems have trouble. The cheese tears or sticks to the blade."

Li has applied for a patent on the technique through the Wisconsin Alumni Research Foundation (WARF), the patent and licensing organization for UW-Madison.

Lasers are devices that produce tight beams of light energy in units called photons, each traveling at the same wavelength and in the same direction. Laser light deposits large amounts of energy in a very small area; in most of today's commercial lasers, this causes extremely rapid, localized heating that cuts a material by melting or even evaporating it, Li says. But when he tried cutting through thin slabs of cheddar with a traditional laser, the cheese did what you might expect: it cooked. "The burning was severe and the smell was bad," Li says, with a laugh. "To make laser cheese processing acceptable to industry, we knew we had to find a cleaner process."

Li turned next to a relatively new class of lasers that emit light in the ultraviolet (UV) range. Unlike conventional lasers, which produce light of longer wavelengths and cut purely by heating, higher energy UV lasers cut through a process called photoablation.

Photoablation occurs when a laser produces photons whose energies exceed the energies of the bonds holding molecules together, Li explains, so that a photon striking one of these bonds immediately breaks it. The millions of photons emitted by a UV laser smash all the bonds in a material, obliterating it molecule by molecule with little or no heating.

In a series of experiments, Li and Choi optimized the parameters of a 266-nanometer UV laser to make exceptionally smooth cuts in cheese without causing burning. To demonstrate the dexterity of the system, the pair has made CAD (computer aided design) drawings and used them to guide the laser in creating intricate slices of mild cheddar.

The main drawback of Li's laser technique is its speed; his current research laser cuts at a relatively slow pace of one inch every 25 seconds. So, although it can carve complicated shapes in thin cheese much more quickly than a mechanical system, the laser loses in a race of straight-up slicing.

At this point, the method is also limited to cutting cheese one-tenth of inch or less in thickness. Both of these limitations can be addressed by employing faster and more powerful UV lasers, which, Li says, are already under development and should reach the marketplace in the near future.

Given their potential benefits — lasers are smaller, cleaner, more accurate, and possibly cheaper and easier to maintain than cutting systems fitted with mechanical blades — Li believes UV lasers eventually could assist in the processing of many other foods, such as meats and vegetables.

"Engineers usually only think about high-tech applications of lasers, such as semiconductors," he says. "One major point of this research is that the use of lasers is possible for processing food. I hope my work will help build a bridge between laser technology and the traditional food industry."