Ever wanted to know what happens to milk between the farm and your glass? This lightly edited story from the Gippsland Murray Goulburn newsletter explains it all really well.
Separation and standardisation
Separation of animal milk, be it goat, sheep or cow is a naturally occurring phenomenon, which has been observed and tinkered with by man for many centuries. Indeed, as recently as the mid-1900s, milk was separated on farm and consigned as cream in cans to the dairy processor, with the whey by-product being fed to the farm’s pigs (MMM note: We had cream cans until the early 1960s when power finally arrived here and a refrigerated vat took their place).
These days, separation of cream from skim milk is done via multi-level centrifugal force separators in a process refined in 1879…Cream, which is lighter than milk, is driven by centrifugal force (MMM note: the same “spinning” force that pushes water out of clothes during the spin cycle of your washing machine) to the surface of the milk and flows off to a holding vessel. Standardisation of milk involves the adjustment of the fat content by addition of cream or skim milk as appropriate.
Along with correct cooling, pasteurisation is one of the most important processes in the treatment of milk. If carried out correctly, this process will supply milk with a longer shelf life. Simply, the process of pasteurisation is to heat milk to 70-75 degrees C but for only five to seven seconds, upon which most bacteria will be killed.
Ultra High Temperature (UHT)
Like pasteurisation, UHT treatment is heat treating milk for a given time at a given temperature…UHT takes the temperature to 135-140 degrees C but only for five to seven seconds. Importantly, the UHT process for milk is a continuous, aseptic (fully enclosed and sterile) treatment and packaging process. Shelf life of six months or more can be obtained if the milk is of the highest quality.
Homogenisation is a process invented in 1899 to stabilise fat emulsion against gravity separation. Essentially, milk is forced through a small passage at great velocity, causing the fat globules to fracture into much smaller ones. The newly-created fat globules will stay free and more stable and be less likely to separate out. This process will also enhance whiteness, flavour and mouth-feel of the milk. The downside of homogenised milk is its restriction in other processes such as cheese making. Also, the product is more susceptible to light damage.
There’s a bit more to the article, including a discussion of ghee, milk powder, casein and yoghurt – topics for other days!