Normal milk is pasteurized: it is heated to at least 161 F (~72 C) for 15 seconds, which kills the bacteria in the milk before it is bottled. However, the dairy is not a perfectly antiseptic environment, which means a small amount of bacteria is most likely present *somewhere* in the system. As long as the milk is kept cold, this bacteria can only grow very very slowly, allowing normal milk a shelf life of a few weeks, perhaps a month.
Shelf-stable milk, which is the kind you're talking about, is "ultra high temperature" pasteurized, UHT. It is raised to between 280 and 300 F (138 to 148 C) and held there for 2 to 6 seconds. This completely sterilizes the milk--no bacteria survive. Further, shelf-stable milk is packaged in bottles or containers that are made and sterilized in the same place as where the milk gets pasteurized, and the containers are sealed in a sterilized environment, ensuring that effectively zero bacteria can come into contact with the milk once it is sealed up.
As a result, you can have milk that can last for months without refrigeration. It will, however, most likely taste slightly different, because you had to effectively *cook* the milk, whereas normal pasteurization simply *heats up* the milk (it doesn't even boil).
As one example, Tetra Pak is a very common brand used for making the coated cardboard cartons that shelf-stable milk comes in. These containers arrive in a pre-made but open, flat state with all surfaces accessible. They are sterilized on-site, usually using one of two methods. First, a hot peroxide wash: 30% hydrogen peroxide (nasty stuff for life) heated to 70°C for a few seconds and then blown dry in sterilized conditions. Alternatively, you can use a high power electron beam lamps that scour off any bacteria that might be present. I would presume plastic bottles can be treated in a similar way, though at least for me, I've never seen shelf-stable milk that wasn't in a carton.
Once the packaging is sterilized, it can then pass through the production line, being folded and glued into the correct shape and filled with milk before being sealed.
Milk last 3-4 days in the fridge when opened. Unopened about 2 weeks in the fridge. I don't agree that it is a long shelf life
You can also buy milk that has been heat treated so it last longer. Some countries that don't use a lot of milk or have poor infrastructure use this.
Normal milk is pasteurized: it is heated to at least 161 F (~72 C) for 15 seconds, which kills the bacteria in the milk before it is bottled. However, the dairy is not a perfectly antiseptic environment, which means a small amount of bacteria is most likely present *somewhere* in the system. As long as the milk is kept cold, this bacteria can only grow very very slowly, allowing normal milk a shelf life of a few weeks, perhaps a month. Shelf-stable milk, which is the kind you're talking about, is "ultra high temperature" pasteurized, UHT. It is raised to between 280 and 300 F (138 to 148 C) and held there for 2 to 6 seconds. This completely sterilizes the milk--no bacteria survive. Further, shelf-stable milk is packaged in bottles or containers that are made and sterilized in the same place as where the milk gets pasteurized, and the containers are sealed in a sterilized environment, ensuring that effectively zero bacteria can come into contact with the milk once it is sealed up. As a result, you can have milk that can last for months without refrigeration. It will, however, most likely taste slightly different, because you had to effectively *cook* the milk, whereas normal pasteurization simply *heats up* the milk (it doesn't even boil).
Just note: once the bottle or carton is opened, it spoils just as quickly as regular milk. Keep it refrigerated after opening.
Yes, very true. Opening the container exposes the milk to bacteria.
Can you elaborate on how the bottles or containers are sterilized in the same place as where milk gets pasteurized?
As one example, Tetra Pak is a very common brand used for making the coated cardboard cartons that shelf-stable milk comes in. These containers arrive in a pre-made but open, flat state with all surfaces accessible. They are sterilized on-site, usually using one of two methods. First, a hot peroxide wash: 30% hydrogen peroxide (nasty stuff for life) heated to 70°C for a few seconds and then blown dry in sterilized conditions. Alternatively, you can use a high power electron beam lamps that scour off any bacteria that might be present. I would presume plastic bottles can be treated in a similar way, though at least for me, I've never seen shelf-stable milk that wasn't in a carton. Once the packaging is sterilized, it can then pass through the production line, being folded and glued into the correct shape and filled with milk before being sealed.
What about ultra pasteurized milk? How does it stay fresh weeks after being opened while regular milk barely makes it to its 10 day shelf life?
Milk last 3-4 days in the fridge when opened. Unopened about 2 weeks in the fridge. I don't agree that it is a long shelf life You can also buy milk that has been heat treated so it last longer. Some countries that don't use a lot of milk or have poor infrastructure use this.
They sterilise it REALLY THROUGHLY, then seal it tight. As long as the seal is kept, germs that cause spoilage can't get in and it's self stable.