In this article, we will answer how long can milk go unrefrigerated, and how to store it properly to preserve its freshness and extend its shelf life.
How long can milk go unrefrigerated?
Milk is perishable and should not be left unrefrigerated for more than 2 hours at 4°C and 1 hour if the temperature is above 32°C according to the FDA, or else the milk will spoil quickly. The crux is to never leave your perishables for long periods of time in the ‘danger zone’.
The extent of spoilage of the milk, that has been left on the counter, depends a lot on the milk quality. Raw milk tends to spoil quicker than pasteurized milk. Milk with a higher initial microbial load will be more prone to spoilage even after pasteurization.
How to store milk correctly?
- Preferably, pasteurized milk should be kept at 3-4°C in the refrigerator.
- Avoid keeping the milk carton in the door to prevent temperature fluctuations.
- Freeze storing milk extends its shelf life for up to 6 months but it is recommended to consume within a month. Frozen milk has a grainy texture and some separated fat. It is best to use in cooking or smoothie/shakes.
How to tell if that milk has gone bad?
Sour milk develops a slimy and grainy texture due to the curdling of casein protein. If the appearance has not changed yet, give it a sniff. If the milk smells sour and acidic, it has gone bad and is unfit for consumption
Drinking spoiled milk in large quantities can result in food poisoning that reflects in the form of diarrhea, vomiting, and nausea.
What should you do with spoiled milk?
If your milk has gone bad and you do not want to waste it, there are plenty of options for recycling it. If the milk has started to turn sour, add a little acid, and make cottage cheese from it. The leftover whey water can be used to cook pasta, soak grains to make them more palatable, or use as an alternative to liquid when baking cakes, muffins, or cookies.
It can also be added to your broth, marinades, or smoothies to get a protein boost.
What is pasteurization?
Pasteurization is a mild heat treatment that is used to kill the non-vegetative forms of bacteria and inactivate enzymes that cause spoilage in fluids like milk, wine, and fruit juices.
The pasteurization of milk is done at 62.8°C for 30 minutes in a batch type process. For the HTST. milk is heated at 71.7°C for 15 seconds.
These are the minimum temperature and holding time requirements to pasteurize milk to kill Coxiella burnetti, responsible for Q fever. Pasteurization does not kill vegetative spores of bacteria, hence, it is important to refrigerate milk after pasteurization to prevent spoilage.
What is UHT milk?
Ultra-High Treatment, also known as Ultra pasteurization is a high heat treatment that sterilizes milk by heating it above 135°C for 2-5 seconds to kill the vegetative spores.
UHT milk has an extended shelf life than HTST milk. It can last 6 to 9 months at room temperature.
Effects of heating on milk quality
Pasteurization reduces the levels of vitamin A, B12, C, E, and folate. However, milk is not a prime source of these vitamins so the reduction in the levels is considered insignificant.
Pasteurized milk results in a considerable decrease of B2 vitamin. Cattle milk is considered an important source of this vitamin.
Pasteurized milk has a more milky white color as compared to the cream-colored or buttery appearance of raw milk. This is because pasteurization involves the homogenization of milk fats prior to heat treatment.
Ultra pasteurization causes Maillard browning of the milk sugars and protein that results in a golden hue and a burnt or cooked flavor.
UHT reduces vitamin C, folate, B12, and thiamine levels in the milk.
Why does milk spoil?
The two species of bacteria that spoil milk are lactobacilli and streptococci. Both of these species are thermostable, hence, they survive during pasteurization and multiply when the environment is favorable. When the milk suffers fluctuations in temperature, streptococci starts to multiply and produce acid by fermenting the milk sugar, lactose. This results in a decrease in the milk ph that inhibits the further growth of streptococcus.
After this, the lactobacillus takes hold and continues to make acid until it cannot multiply anymore due to low acidity. This low ph denatures the casein protein structure and causes it to curdle up leaving behind the hey protein liquid and the casein is filtered to make cottage cheese.
In this article, we answered how long can milk go unrefrigerated, and how to store it properly to preserve its freshness and extend its shelf life.