Finding a cure for blind Swiss cheese
Swiss cheese is one of the precious few items on my kindergartner’s list of preferred foods that does not qualify as either a dessert or a pastry. The dry, somewhat nutty cheese seems slightly incongruent with her usual tastes, although perhaps some of the appeal is the unique shape of the cheese with its signature holes, or “eyes” as they’re known to fromagers. The value of these eyes can’t be overlooked for most turophiles (lovers of cheese!), especially after a brief crisis of eyeless, or blind, cheese cropping up in Switzerland around 15 years ago.
There are a number of ways the eyes in Swiss Cheese can go wrong, ranging from streuble, wherein too many eyes near the outer surface of the cheese wheel, to frogmouth, where the eyes are the wrong shape. These issues are all tied to the source of the eyes, which is carbon dioxide bubbles expelled by Propionibacterium freudenreichii bacteria, which is also responsible for the cheese’s key flavors. Many of these other issues were already tied to conditions affecting the performance of the P. freudenreichii, but the wave of blind cheese was something else entirely. There was a fundamental hole in cheese maker’s knowledge of what caused the eyes to form where they did in the first place.
The cause of the carbon dioxide clusters
One possible clue was a seasonal pattern in the blind cheese turning up. Cheese made in the summer, when cows grazed out in fresh grass, was more likely to be blind than in the winter, when the cows ate dry hay in the barn. It turned out not to be an issue with the cows diet though, as much as those shifting environments. When the cows were milked near the hay, some particulate would get mixed into the milk. Those tiny bits of hay would then act as seeds for the carbon dioxide bubbles cluster around, forming eyes as they grew large enough. The cows eating fresh grass didn’t have as many “seed” particles for the bubbles, and so the eyes weren’t as consistent.
The reason for the spike in blind cheese 15 years ago was then that the milk being used was suddenly too clean. As part of European Union regulations, cows were no longer being milked in the hay barn into open pales, instead being milked with automated, closed pumps. This really reduced the amount of hay particulate present, which then needed to be reintroduced after the milk was processed. With this new understanding and workflow, the eyes have actually become more controllable. For markets like Italy, less hay is added so the carbon dioxide makes fewer but larger bubbles, and thus larger eyes. For delis, the opposite formula is used to created smaller eyes, which are easier to slice.
Source: How Does Swiss Cheese Get Its Holes? by Nicola Twilley, The New Yorker
