Q How does Swiss cheese get its holes?

A Wisconsinites love their cheese, but what’s fascinating about Swiss cheese is what’s missing.

In the manufacturing world, these holes in the staple cheese are referred to as “eyes.” The eyes form during the ripening stage when a bacteria nicknamed “props” is inserted into the cheese. The props then consume the lactic acid in the cheese and convert it into carbon dioxide, which is a gas.

As pressure grows within the cheese and more gas is produced, it pushes the curd apart. So, in short, it is gas bubbles that create the eyes in the shape of circles. Since the cheese is not a liquid, Fromagination cheese monger Sam Smith said that the bubbles can’t reach the top and will go as far as they can until the cheese firms up.

Swiss cheesemakers encourage the cheese to open its eyes even further by transferring the cheese to a warm room for a few weeks, said John Lucey, director of the UW-Madison Center for Dairy Research. The cheese is softer at higher temperatures so it’s easier for the curd to form bubbles. The size of the eye depends on the amount of gas produced.

According to Lucey, Swiss cheese should have large eyes and not too many of them. Lots of small holes is not a traditional characteristic of Swiss cheese. When the cheesemaker sees the block start to swell and bulge as the holes form, they can bring it into refrigerated storage to halt any further development, he said.

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The props give the cheese a unique taste as do many different properties during production, Smith said.

However, the eyes have gotten smaller over time with cleaner processing centers, according to the Agroscope Institute for Food Sciences. In previous years, barns and older production centers let larger hay particles into the process which leads to bigger eyes.

The U.S. Department of Agriculture feared that cheesemakers might take advantage of these growing eyes and have regulated their size. In 2000, eye standards were adjusted from 11/16ths of an inch to 3/8 of an inch.

Smith said if there were no regulation, cheesemakers would throw in a ton of bacteria so there would be more eyes and less cheese in the blocks that they sell. “So they’d be selling less cheese for the same price.”

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Send questions to: justaskus@madison.com; Just Ask Us, P.O. Box 8058, Madison, WI 53708.