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Question of the day: When does cheese go bad?

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A friend of a friend mentioned at lunch recently having to pitch some cheese she had been planning to use for eggplant parmesan because it had gone bad, raising the private question: "When exactly DOES cheese go bad?" ... followed by the even more private one "Cheese goes bad?"

We put the issue before St. Paul Cheese Shop Manager Benjamin Roberts. It turns out these questions aren't all that embarrassing after all. Roberts said attendees at a cheese class he hosted just this week brought up the question of when to know when your cheese has turned.

There are two main things to consider, Roberts says.

1. Smell. If the cheese has a pungent, ammonia aroma that's a good indication it's no longer suitable. Roberts says a little bit of an ammonia scent is ok, but any type overwhelming scent is not.

2. Taste. If you can detect any type of bitterness to your cheese, it's probably a sign that its days are numbered. If it tastes wrong, it probably is wrong.

To a lesser extent, Roberts says, a quick visual inspection can tell you something about whether a cheese is past its prime as well. Any type of drying out is a good sign that the cheese has seen better days. This doesn't necessarily mean the cheese is inedible but Roberts says, "If it's drying out, then not going to be as delicious."

With some softer cheeses (Roberts mentions Humboldt Fog) -- which are gooier toward the outside when fresher -- the expansion of the gooeyness toward the more flaky, crumbly center is a sign the cheese is overripe, though this is more difficult thing for amateurs to discern.

These rules of thumb apply moreso to blue cheeses and soft cheeses, like brie, and to a lesser extent some harder cheeses. As a rule of thumb, soft cheeses go bad quicker than hard cheeses. "The clock is ticking slower on harder cheese than on soft," Roberts says.