Milk Processing

The following topics in this chapter contain relevant information on milk processing:

At the Milk Processing Plant

What About the Packaging?

Recycling Milk and Yogurt Containers

At the Milk Processing Plant

Tankers transport the milk from dairy farms to the nearest milk processing plant. On arrival, milk from the tanker is tested again in a laboratory to ensure that it has been kept at or below 4 degrees Celsius during transport, and delivered within 24 hours of milking. The tests also monitor protein levels and check for the presence of bacteria and antibiotics. The milk is then pumped into large insulated vats at the factory.



What About the Packaging?

At the factory, milk is sent through a processing line to be packaged in cartons or bottles. Cartons are made from cardboard lined with a polyethylene plastic.

The cartons, in varying sizes, are flat and then are formed into their proper shape in a machine just before being filled.

Once the correct amount of milk has been put in, the carton is heat sealed, stamped with the use-by date and packaged in milk crates which are stored in a huge cool room until they are collected from the factory.

In the past, milk was always packaged in glass milk bottles (and some countries still have milk delivered this way).

Milk cartons first came to Australia in 1958, when the Model Dairy in Melbourne began packaging milk in 150 ml and 500 ml Tetra Pak tetrahedron-shaped cartons. At the time, 160,000 new glass bottles were needed in Melbourne alone every week to keep up the delivery of 1.3 million bottles of milk a day.

Fast facts

In 1968 in Victoria, only about 1% of milk was sold in cartons, but by 1972 milk cartons had 20% of the market.
In 1970, the blow-moulded disposable plastic milk bottle was introduced.
In 1987, only about 2% of milk was still being sold in glass bottles.

Recycling Milk and Yogurt Containers

Whether your milk comes in a plastic bottle or cardboard carton, the empty container is a resource that can be turned into new products.


Recycling Plastic Milk Bottles

High density Polyethylene
Plastic identification Code

Plastic milk bottles are made from high-density polyethylene (HDPE). After collection from your kerbside recycling bin, they are separated from other types of plastic at a materials recovery facility (MeRF) and then baled. The baled bottles are sent to reprocessing plants where they are chopped into small flakes and washed using recycled water to remove any residual milk, labels and caps. The flakes are melted and filtered to remove any other contamination and the molten plastic is then extruded into strands and chopped into pellets ready for re-moulding into new products such as outdoor furniture.

Recycling Yogurt Tubs

Empty yogurt tubs of all sizes can also be collected for recycling into new plastic products. Yogurt containers made from a range of plastics, such as HDPE, polypropylene (PP) or rigid polystyrene (PS) can also be processed into pellets for recycling. Look for a Plastic Identification Code (the universal recycling symbol with a number in it) on the tub to show the type of plastic from which it is made. HDPE is 2, PP is 5 and PS is 6.


The plastic pellets are blended and then heated to a molten state before being moulded into a range of recycled plastic products, including planking, signs, outdoor furniture, benches, bollards, bins and more. These products are coloured right through, so they do not require painting, and they are also graffiti proof. They will not split, rot or be eaten by termites and can last five times longer than the timber alternative, even in harsh coastal weather conditions. For this reason, the end product is sometimes referred to as ever-wood as it is a durable, long-lasting substitute for wood.

Pellets from recycled plastic milk bottles and tubs can also be mixed with virgin pellets and made into non-food containers for products such as detergent and shampoo. Recycled HDPE plastic cannot be recycled into packaging for food products because it has a low melting point and bacterial contamination is a possibility.

Recycling Milk Cartons

If you have an empty milk carton, think 'office-quality paper' and choose the recycling bin. Cartons containing milk, flavoured milk and custard are made from liquid paperboard (LPB). A one-litre LPB carton is made from the equivalent of five sheets of office-quality A4 paper.

LPB gets its strong card-like properties from a mixture of hardwood and long softwood fibres and this is what makes it so good for recycling. It is also bleached in the initial production process, so the recycled paper product requires no further bleaching.

After collection, the LPB is separated at the MeRF and baled for recycling. At the paper recyclers, the LPB is shredded and washed to remove any residual milk products. The cartons have a plastic/polyethylene coating to waterproof the paper, and this is separated from the paper and strained off for reuse by plastics recyclers. The shredded cartons are then reprocessed into a pulp, formed into sheets of paper, pressed and dried. The result is high-grade office-quality paper!

Benefits of Recycling

Recycling your milk and yogurt containers has enormous benefits for the environment. Not only are materials diverted from landfill when we recycle, but we also save natural resources and reduce our environmental impact.

Fast Facts 

  • When a product is made by recycling materials, it uses far less energy than if we were to make that same product from raw materials, such as coal, iron ore, oil and trees.
  • Every time you recycle 41 plastic bottles, enough energy is saved to run a refrigerator for one hour.
  • A 100% recycled plastic seat for two contains the equivalent of 680 two-litre milk bottles and saves six cubic metres of landfill.
    Every tonne of LPB recycled saves 2.5 barrels of oil; 4,100 kW of electricity; 31,780 litres of water; four cubic metres of landfill and 13 trees.

When we purchase products that are packaged in materials we can recycle, it is important to make sure that we follow through and recycle them.

For schools this means setting up a collection system for milk cartons, bottles, and yogurt tubs. If they contain residual milk or yogurt, they could become very messy and smelly, so here are some useful tips:

  • Use an open bin or tub for collection so that you can see what is going in and check that it is not contaminated by food scraps.
  • Put a bucket with water and tongs at the collection point so that students can rinse the container before placing it in the bin.
  • Empty the bin or tub every day, or every second day, so that mice, ants and other insects do not become a problem.

As technology improves, and more opportunities arise to capture materials for recycling, it is important to 'close the loop' and choose products with a recycled content. It is all about reducing the volume of valuable resources that are going to landfill and recognising the value of the containers we use every day.

Now go to About Dairy Products.