Question

reasons for milk being supplied in glass bottles later in plastic bags and now in tetra pack and through vending

Answer 1

     Long ago, milk was supplied in cans personally at homes by Dudhwalas - milk vendors.  Then milk was supplied in bottles from the distillation centers.  That was to keep the milk hygienic.  It was convenient and healthy to supply that way.  The bottles were re-used.

     The milk bottles were heavy.  Newly introduced plastic was very light, strong enough to hold milk, and cheap too.  As plastic was available abundantly and cheaply, it was used by the manufacturers.  There was no danger of milk bottles getting broken.

     Then the environment is getting polluted due to the non-bio-degradable plastic and polythene packing. So the manufacturers shifted to thick paper pulp packing.  The tetra packs are introduced to save packing space.  Their space utilization is 75% or more.  They are more efficiently transported that way.  The packing is strong.  They milk can stay fresh and unspoilt for a long time.  The tetra packing materials are bio-degradable.  They are easy to handle and can withstand weight on them.

The tetra pack is a tetrahedron shaped and plastic coated paper pulp material.  It is invented by a multinational company for packing beverages and foods.  It uses minimum amount of material for maximum volume capacity for sufficient strength.  The material is also very cheap.

The inventors of tetra pack have received awards for best invention in food and packaging industries and for the best application of mathematical principles.