Will grapefruit mould and how long?

Yes, grapefruit can mold if stored improperly or kept for too long. Typically, if kept at room temperature, grapefruit may start to show signs of mold within a week or two. In the refrigerator, they can last longer, usually up to three weeks, but it's important to check for any signs of spoilage regularly. Proper storage in a cool, dry place can help extend their freshness.