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Q: Sometimes my yogurt container bulges at top even though it’s not past its expiration date. Is it safe to eat?

A: Expiration dates on packages assume the food has been stored properly. If the yogurt is a fruit-on-the-bottom type, it may have been inadequately refrigerated, perhaps at the grocery store or in transit, causing the fruit to ferment and release gases. This would cause the lid to bulge.

Fermented fruit is not harmful, but since you can’t really know what causes the swelling, it’s best to toss the yogurt. It may taste “off,“ anyway.

Discard other swollen packages as well, such as fruit juices, fruit packs, cheese, meat patties, and especially bulging cans; the last can harbor deadly Clostridium botulinum toxins, which aren’t destroyed by cooking.

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UC Berkeley Wellness Letter, June 2011