At some point in your life, you may have grabbed a container of yoghurt from the fridge and put a heaping spoonful in your mouth without paying attention only to discover to that it's inedible. If you're lucky, you haven't yet swallowed the spoiled yoghurt. If not, you may have some slight digestive trouble later. Avoid this problem by paying attention to what it looks and smells like.
Look at the expiration date on the yoghurt container. If the yoghurt is several days past the expiration date, it doesn't necessarily mean it is spoiled, but it's a good indication of how much longer you can safely eat it. According to the website Still Tasty, yoghurt in the refrigerator is generally safe 7 to 10 days after the expiration date on the packaging.
Look at the yoghurt. Open the container and look for mould or any other irregularities. Discard if you see any signs of mould, or if the yoghurt is starting to look lumpy like cottage cheese.
Smell the yoghurt. If the yoghurt smells like sour milk, discard it immediately. A bad smell is a sure sign of the yoghurt being spoiled.
To keep yoghurt for longer, place it in the freezer, where it an last for 1 to 2 months at best quality. For yoghurt that is expired but does not yet have a bad smell or appearance, use the yoghurt to make a moisturising face mask if you are concerned about consuming it. Blend a cup of yoghurt with one cup of puréed cucumber and a half a cup of honey for a homemade facial mask.
Discard yoghurt that has been left out at room temperature for more than two hours.