Certain kinds of yogurt - organic and probiotic varieties that contain live and active cultures or “good” bacteria, have a very long shelf life. These kinds of yogurt will just continue to ferment and the healthful bacteria will produce increasing amounts of lactic acid that will simply make the yogurt more tart, but certainly not harmful. As a general rule, if kept undisturbed in the refrigerator and the seal is unbroken, organic and probiotic yogurts can be kept for several weeks beyond their use-by date. “However, the more traditional and conventional kinds of American yogurt that are made from milk, pectins, fillers and other compounds that add texture, will spoil quite quickly because they contain a certain type of protein that’s prone to spoilage,” says Shelke. “Where these are concerned, consumers should abide by use-by dates, as they’ll taste very bad and smell terrible once past their best.”
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