|MadSci Network: Microbiology|
The holes in Swiss cheese are caused by gas formation during fermentation. The bacteria which are used in the production of the cheese produce gas (mostly carbon dioxide) as a by-product. The gas cannot escape from the interior of the cheese, and so collects in pockets or holes in the cheese itself. The starter cultures used for Swiss cheese are selected for their ability to produce this phenomenon, in addition to other important characteristics, such as the flavor that they impart to the cheese.
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