Leaving milk in a car, especially on a warm or hot day, is not recommended as it can quickly spoil due to the temperature fluctuations. The time it takes for milk to go bad in a car can vary depending on factors such as the outside temperature, the temperature inside the car, and whether the milk was refrigerated before being left in the car.
In general, when milk is left at room temperature (around 68-72°F or 20-22°C), it can start to spoil within two hours. If the outside temperature is higher, say during a hot summer day, the milk can spoil even faster, potentially within an hour or less.
Bacteria can grow rapidly in milk when it's in the temperature danger zone, which is between 40°F (4°C) and 140°F (60°C). At these temperatures, harmful bacteria can multiply, leading to the spoilage of milk and increasing the risk of foodborne illnesses if consumed.
To ensure milk stays fresh and safe to drink, it's essential to keep it refrigerated at all times when not being consumed. If you accidentally leave milk in a car on a warm day for an extended period, it's best to discard it to avoid any health risks associated with consuming spoiled milk.