The hazards of spoiled milk depend on the kind of milk it is. Spoiled pasteurised milk and raw milk are completely different dangers. The smell of ruined milk is usually enough to warn you that you do not want to drink it. If you accidentally swallow raw milk, the very thought of it may make you sick to your stomach.
In the 1800s, Louis Pasteur made life safer and easier for all of us. He developed a process for heating milk (or wine or beer) to just below the boiling point and rapidly cooling it. This process kills many of the bacteria that are harmful and potentially fatal. This process makes milk safer and keeps it fresher longer. When pasteurised milk spoils, it is not likely to be fatal but can be dangerous to young people and those with compromised immune systems, according to Healthline. The first symptom is usually diarrhoea. It can then cause nausea, abdominal cramps and vomiting similar to other food-borne illnesses. Many recipes use spoiled milk as an ingredient. The spoiled milk is heated, killing bacteria. Most milk bought in a grocery store is pasteurised, and this is clearly indicated on the label.
Milk that has not been pasteurised is called raw. This milk may contain salmonella, Escherichia coli, campylobacter and the bacteria that cause illnesses such as tuberculosis, diphtheria, streptococcal infections, typhoid fever and other illnesses, according to the Centers for Disease Control. Though many foods carry food-borne illnesses, raw milk is one of the most dangerous. Drinking contaminated raw milk, at a minimum, causes several days of severe cramping, diarrhoea and vomiting. At the worst, contaminated milk causes kidney failure, paralysis, several chronic conditions and even death. Raw milk is especially dangerous to young children, pregnant women, elderly people and those with weakened immune systems, such as a transplant recipient, cancer patient or someone with AIDS/HIV. Raw milk is found in many farmer's markets and organic food stores. If the word "pasteurised" is not printed on the label, it probably is not pasteurised. If in doubt, ask the farmer or market owner. If you are not able to verify it has been pasteurised, it is not worth the risk to drink it.
Raw milk is never completely safe. Keep pasteurised milk in the refrigerator, and keep the refrigerator at 2.78 degrees Celsius. Watch the expiration dates and throw it out when the date is passed. Pasteurised milk begins to spoil at 7.22 degrees Celsius. For every -7.78 degrees C rise in temperature, the spoilage rate of milk doubles. Milk spoils even faster if left uncovered. Even if milk is well within the expiration period, it spoils quickly if left out. The warmer it is, the more quickly it spoils. If you encounter milk that has been left out and allowed to warm, toss it out to be on the safe side.
The first thing most people notice is the sour smell of ruined milk. This is usually enough to deter an adult, but children may go ahead and drink it anyway. It pays to be vigilant about tossing old milk and food if there are young people in the house. If the milk is allowed to spoil further, it forms a solid crust on the top while the liquid in the bottom becomes clear. The milk eventually curdles, forming solid lumps similar to cottage cheese. If an adult ingests a small amount of spoiled pasteurised milk, he probably may not need medical attention unless he has a compromised immune system. If a child, elderly person or someone with a weak immune system ingests spoiled pasteurised milk, contact a doctor. If stomach pains, nausea, cramping, vomiting, diarrhoea or any other unusual symptoms occur in any person after ingesting raw milk, seek medical attention immediately.