If you’ve ever decided to take a look around yourself in the grocery store, you’ve probably noticed how extensive the dairy section is. There’s dairy, nut, oat, and powdered milk! How do you prevent your milk from spoiling, though? Is it the same for all types of milk?
Milk should never be stored at room temperature if it’s only pasteurized. Regular pasteurized milk is the most popularly treated milk in the United States and must be kept refrigerated at all times. However, other kinds of milk, such as ultra-high-temperature pasteurized milk, can be stored at room temperature before it’s opened.
Do you have to refrigerate canned milk? What about non-dairy milk? What happens to milk when left at room temperature? Keep reading to find out!
What Happens to Milk When It’s Stored at Room Temperature?
Milk will spoil after a few hours of sitting out at room temperature. Spoilage combines heat and bacterial multiplication as the milk becomes a more favorable environment for bacteria. This can cause the milk to turn sour as the lactose converts to lactic acid.
The simplest answer to “what happens to milk at room temperature?” is it turns sour and curdles. However, the process is more complex than simply turning sour and unpleasant.
Your milk has actually become a breeding ground for fungus and bacteria.
Milk must be refrigerated in the United States. This is because the United States only pasteurizes its milk versus other areas of the globe where they use ultra-high-temperature pasteurization (UHT).
Pasteurization kills most fungi and bacteria, but not all. When pasteurized milk is kept under 40 degrees Fahrenheit (4 degrees Celsius), it’s unfavorable to the reproduction of bacteria and fungi. The cool temperature prevents these bacteria and fungi from reproducing and spoiling your milk.
If your milk is kept at a warm temperature, these bacteria can start to reproduce. This can cause digestion issues and food poisoning if consumed.
Does Unopened Fresh Milk Need To Be Refrigerated?
Unopened fresh milk must be refrigerated. Unopened milk will last longer in the fridge than opened milk. You can keep unopened milk in the fridge for between 10-12 days, whereas opened milk can only be stored between 3-6 days.
Unopened milk can be stored longer than opened milk, but this isn’t due to the temperature of the milk. Both opened and unopened milk should be stored at below 45 degrees Fahrenheit and above 32 degrees Fahrenheit (7-0 degrees Celsius).
However, unopened milk doesn’t get exposed to as much bacteria as opened milk. Whenever you open a milk jug, you expose the milk to the bacteria and particles in the air. This can cause bacteria to multiply and spoil.
Every time you open your milk, it’s exposed to more bacteria. It’s important that you keep milk covered when not using it and avoid exposing it to air particles.
How Can You Protect Milk Without a Fridge?
There are several ways to protect your milk when it’s outside of the fridge. The best method is to keep your milk inside an insulated cooler with ice or freezer packs. Avoid opening it to keep the environment below 45 degrees Fahrenheit (7 degrees Celsius).
Some of the best ways to store your milk without a fridge include the following methods:
- Insulated ice bin with ice
- Freezer packs
- Dark bin with ice
- Sealed container with other cold foods
- Lunch box next to other cold foods
- Keep milk close to water bottles
- At the supermarket, store your milk next to frozen food
You might need to store your milk outside of your fridge for several reasons. If you’re bringing milk for lunch or a picnic, keep it stored inside the lunch box or insulated container. Keep ice and cold foods close to the milk to keep each other cold for longer.
However, in this instance, you should pour the milk you’ll need into an insulated cold bottle. Don’t bring the whole jug with you in your lunch box. Not only are these jugs bad for insulation, but if the milk gets warm while you’re out, you’ll have to throw away the whole jar.
If you lose power, don’t take your milk out of the fridge. Purchase a few bags of ice and avoid opening the fridge as much as possible. This should keep the milk cool enough until your power comes back on.
If your fridge breaks and you believe it will remain broken for several days, you shouldn’t keep your milk in the fridge. You should keep your milk in an insulated bin with ice and replenish the ice every day. This should keep your milk cool until the fridge is repaired.
You can learn more about milk storage and preservation in our article, Can you freeze milk?
What Milk Can Be Left Unrefrigerated?
Generally, dehydrated, canned, and ultra-high-temperature pasteurized milk doesn’t have to be refrigerated.
These kinds of milk have been treated for shelf stability and won’t spoil at room temperature. However, if they’re opened or prepared, they must be refrigerated and stored for ten days or less.
Ultra-high-temperature pasteurization is a sanitation process that flash heats milk to extremely high temperatures. UHT milk is heated to above 300 degrees Fahrenheit (149 degrees Celsius) for 1-3 seconds. This high heat kills almost all bacteria and fungi without cooking the milk.
This process sets it apart from pasteurized milk. Pasteurized milk is slowly heated to lower temperatures, killing many bacteria, but not all. This makes it much safer to drink than raw milk, but not shelf-stable.
UHT milk can be stored at room temperature for several years as long as it’s unopened. Once opened, it must be stored in the fridge.
Canned milk is also heated to high temperatures and sealed. This prevents oxidation which causes milk to spoil and degrade. Canned milk can be stored at room temperature for several years but must also be refrigerated after it’s opened.
Dehydrated milk has all the moisture removed through a heating process. Only the fat, sugar and other hard substances remain, leaving a powder. This milk can be stored at room temperature for several years unless it’s been prepared, Once you add water to this powder, you must refrigerate it.
Can Non-Dairy Milk Be Left Unrefrigerated?
Non-dairy milk must be refrigerated unless it’s been specially treated. Some non-dairy milk is shelf stable like traditional dairy milk if it’s been ultra-high-temperature treated. However, traditionally pasteurized non-dairy milk must be refrigerated like dairy milk.
Some people think non-dairy milk can be left at room temperature without spoiling because it doesn’t contain dairy. Although many non-dairy kinds of milk have fewer bacteria than dairy milk, they aren’t immune to spoilage.
Non-dairy milk contains fats, sugars, and carbohydrates. All of these components, combined with the moist, warm environment, make for the perfect breeding ground for bacteria.
The only ways non-dairy milk can be left out is for the following reasons:
- Dehydrated milk powder
- Canned non-dairy milk
- UHT non-dairy milk
This is not unlike dairy milk which can be stored at warm temperatures if properly processed. Keep these specially treated milks in their original, sealed containers in a dark, cool, dry place. Once opened or prepared, store in a sealed container in the fridge and date for 10 days.
Why Does Some Milk Not Need To Be Refrigerated?
The main reason some milk doesn’t need to be refrigerated is it’s heated to high temperatures. This process kills almost all bacteria. After this process, the milk is hermetically sealed to prevent any foreign bacteria from infecting the milk and spoiling it.
It’s very important that UHT milk gets sealed and stored properly. You shouldn’t keep your milk in a sunny area since the sun can damage the container your milk is stored inside.
Keep your UHT milk inside its original container until you’re ready to use it.
When milk is hermetically sealed, it means it’s impenetrable. This seal can’t be broken unless purposefully slit, cut, or opened. This helps guarantee there are no holes or punctures in the package that can damage the milk.
Other milk varieties are either canned or dehydrated.
Dehydrated milk has no moisture and thus is immune to most bacterial development. Most bacteria need moisture to propagate; thus, dehydrated milk won’t spoil until moisture is added.
However, if you live in a very humid environment, this moisture can get into the dry milk if it’s stored for several months unsealed. This can cause the milk to clump into hard balls which smell sour. You should not use this and should throw it away.
To prevent this from happening, keep your dehydrated milk inside a sealed container after you open the package.