I wanted to eat cereal at work so I poured some milk into an empty water bottle and brought it with me. It stayed in the refrigerator until quitting time. I put the bottle into my backpack and drove home. I tossed my backpack onto my bedroom floor and went to bed (I get off work at midnight). In the morning I remembered that I left the milk in my backpack so I thought the milk would be sour. I opened the bottle and took a whiff. It smelled ok. I cautiously took a sip. It tasted fine. I put the bottle in the fridge and will have some cereal later.