INTRODUCTION
Marco Polo in the 13th century reported that soldiers of Kublai Khan carried sun-dried milk
on their expeditions. In more recent times, milk has been dried in thin films on heated
rollers. The earliest patents for this process date from the turn of the century. Such roller
drying was the main means of producing milk powders until the 1960s when spray drying
took over. Milk powder manufacture is now very big business. New Zealand produced and
exported over 450 000 tonnes of milk powder during the 1993/94 dairying season, earning in
excess of NZ$1 billion.
Milk powder manufacture is a simple process now carried out on a large scale. It involves
the gentle removal of water at the lowest possible cost under stringent hygiene conditions
while retaining all the desirable natural properties of the milk - colour, flavour, solubility,
nutritional value. Whole (full cream) milk contains, typically, about 87% water and skim
milk contains about 91% water. During milk powder manufacture this water is removed by
boiling the milk under reduced pressure at low temperature in a process known as
evaporation. The resulting concentrated milk is then sprayed in a fine mist into hot air to
remove further moisture and so give a powder. Approximately 13 kg of whole milk powder
(WMP) or 9 kg of skim milk powder (SMP) can be made from 100 L of whole milk. The
milk powder manufacturing process is shown in the following schematic and is described in
detail below.