Why plastic bottles widely used on milk storage
Keeping milk chilled is critical to keeping it fresh. Whether you are storing raw milk or pasteurized milk, you should always keep it in the refrigerator.
It should never sit out at room temperature. If all you plan to do with your milk is drink it, then store it in clean glass jars, 2-quart size or smaller.
Every time a jar is opened and exposed to air, there is the possibility of contamination.
For now, plastic container for raw milk storage is most popular in the world.
Plastic milk containers are plastic containers for storing, shipping and dispensing milk. Plastic bottles, sometimes called jugs, have largely
replaced glass bottles for home consumption. Glass milk bottles have traditionally been reusable while light-weight plastic bottles are designed for single trips
and plastic recycling.
Packaging of milk is regulated by regional authorities. Use of Food contact materials is required: potential food contamination is prohibited.
Strict standards of cleanliness and processing must be followed.
The most common material in milk packaging is high density polyethylene (HDPE), recycling code 2. Low density polyethylene (LDPE), and polyester (PETE),
are also in use. Polycarbonate had been considered but had concerns about potential contamination
Blow molded plastic milk bottles have been in use since the 1960s.   HDPE is the primary material but polyester is also used. A wide variety of milk bottle
designs are available. Some have a round cross section while others have a more square or rectangular shape. A special flat-top square milk jug was recently
developed to maximize shipping and storing efficiency but had some difficulties in dispensing. Many milk bottles have integral handles.
Milk bags are also in use. The milk is sold in a plastic bag and put into a pitcher for use.Small individual containers of milk and cream are often thermoformed
or injection molded and have a peelable lid. These are often used in restaurants.
The shelf life of pasteurized milk in HDPE bottles and LDPE pouches has been determined to be between 10 and 21 days when stored at 4-8 °C. Other factors
such as light and temperature abuse have effects. Shelf life can be extended by ultrapasteurisation and aseptic processing.
Milk containers for retail sale must contain the same amount of milk as indicated on the label. To be acceptable to consumers, the containers must also appear
to be completely full. Therefore, the volume of the container must be precisely controlled.
The designer of a die for a blow moulded bottle can never be completely sure of how much the finished bottle will hold. Shrinkage always occurs after the item
is released from the mould. The amount of shrinkage depends upon many factors, including cycle time, inflation air pressure, time in storage prior to filling, storage
temperature, and more.
A volume adjuster insert is one way to slightly adjust the volume of a bottle, without building a completely new mould. A volume insert attaches to the inside of
a mould, creating a circular indentation on the side of the finished bottle. Different size inserts can be used as manufacturing circumstances change,
for example mould temperature or cooling rate. The volume of finished bottles is periodically measured, and volume inserts are changed as needed.