I had cereal for breakfast this morning, and I sniffed the milk and it smelt fine, tasted fine etc. So I used it, there wasn't much left in the carton at that point. About 30 minutes later I decided to make a coffee and used the last of it and opened a new one. I always heat the milk in the microwave for coffee/cocoa and I did that this morning. I drank 95% of the coffee and then noticed curdled milk in the bottom of the cup?! The old milk wasn't due to expire until the 13th and the other one was just purchased yesterday? It was my sisters lactose free milk so maybe it reacted differently to being heated? Either way I'm pretty concerned as I consumed a fair bit of it between the cereal and the coffee....I just really need some reassurance.