People who eat yogurt that has expired sometimes suffer from nausea, abdominal cramping, diarrhea, and vomiting. These symptoms can range from mild to severe.
Eating spoiled yogurt will often provoke the same bodily responses as other foodborne illnesses. Abdominal cramping may be the first symptom and it could take a few hours to begin. This is usually followed by diarrhea and vomiting which happen as the body tries to rid itself of the harmful bacteria in the yogurt. Food-borne illnesses can last anywhere from a few hours to a few days and, if symptoms persist or continue to worsen, it is advised to seek medical treatment.
As long as the yogurt has been properly stored and remains sealed, it will usually last from seven to 10 days past its expiration date. It's pretty easy to tell when yogurt has gone bad. It shouldn't have an odd smell, be watery and be discolored in any way. If it smells off or tastes "funny," throw it out.
Yogurt should always be stored in the refrigerator and most can be frozen for up to two months in either its original packaging or in a airtight container. However, yogurt stored in the freezer loses some of the probiotic advantages, as some of its bacteria dies off in the freezer.