Homogenised and pasteurised are probably words that sound somewhat familiar, appearing on the majority of milk and dairy products that you can buy today. But they’re big words and no description is given, so what do they actually mean?
Both are techniques of improving the safety and quality of the milk and I’ll discuss the process, benefits and costs of each.
The process of pasteurisation is named after the man who developed and patented it, Louis Pasteur. While scientists of the time had recognised that heating beverages could prevent them from spoiling, Pasteur demonstrated that it was bacteria that caused spoilage, rather than by a purely chemical process as was previously accepted. From this point, he went on to show exactly how hot the beverage had to be heated and for how long to prevent spoilage and bacterial diseases.
He originally had been commissioned to develop the process for use in wines and beers, and succeeded in 1862, concluding that the drink had to be heated somewhere between 40 and 100 degrees Celsius for several minutes in the absence of air. If it was heated a lower temperature (which better preserves the flavour), it had to be heated for longer, but if higher temperature was used, it did not have to be heated for as long … as the bacteria are killed more quickly at higher temperatures.
The application of pasteurisation for commercial milk sales did not occur until 1882, spearheaded by a doctor named Abraham Jacobi, who believed that raw milk was killing babies who consumed it. He introduced pasteurisation into the US and it spread to become common practice and then mandatory throughout the early twentieth century. Unsurprisingly, infant mortality rates also fell (from 240 per 1000 to only 71 per 1000 in 7 years) and the spread of tuberculosis slowed (a study done in 1895 found that nearly 25% of herds carried tuberculosis in their milk).
There were some hiccups in the process as the exact time and temperature required were discovered. Some producers were heating too low (leaving bacterial diseases active in their milk) and others were heating too high by boiling it for extended lengths of time (this caused albumin, a protein that makes up 60% of blood protein, to become indigestible and detrimental to the children who drank it).
But eventually they worked it out and today, milk is generally pasteurised at 72 degrees Celsius for 15 seconds. UHT milk (long-life milk) is Ultra-Heat Treatment, meaning that it is heated to 138 degrees Celsius for at least 2 seconds, killing bacteria so effectively that it has a shelf life of 6-9 months (before opening), instead of the 2-3 weeks for standard milk. However, as I’m sure you know, UHT milk does have a different taste due to this method of pasteurisation and so our normal fridge milk remains popular.
Is pasteurisation still necessary today?
Pasteurisation has many critics, found in promoters of organic foods, who claim that this process is not necessary and strips nutrients from the milk. In one such article, the author noted that 412 Americans had become sick after consuming homogenised and pasteurised milk, while only 116 cases of sickness had been reported from patients consuming raw milk. Initially, it sounds suspicious, but applying a little bit of critical thinking, it is easy to realise that far, far fewer people consume raw milk and the proportion of consumers who became sick from each milk type would be higher for raw milk consumers. Another sneaky case of statistics being warped to draw incorrect conclusions!
But using some other statistics, in 1997, researchers found up to more than a 1/3 chance of having some harmful bacteria in pooled bulk raw milk. Similarly, in 2006 another study found similarly high pathogen counts where the dairy farmers were often unaware of the risk.
To quote Professor H. Douglas Goff of the University of Guelph, “It’s possible to make pathogen-free milk on a very small and very clean farm … But scaling that up, that’s where it falls apart.”
So people who believe that raw milk is far better than pasteurised can be safe getting milk from small, clean farms, but if 1/3 of commercial milk is contaminated once pooled together, we can’t safely sell raw milk on a large scale. Additionally, raw milk supporters claim that compounds such as Vitamin C are deactivated during pasteurisation. That’s true, but milk is not a major source of any of these compounds and can generally easily be gained in sufficient quantities from fruit, vegetables or other foods.
So there is diminished nutritional quality, but at the benefit of not getting sick from nasty bacterial diseases, when you should be getting sufficient other nutrients anyway. So pasteurisation is probably the best way to go!
Unlike pasteurisation, homogenisation has to do with the aesthetic value of the milk … making it smooth and allowing separation into full cream, skim and lite milk types.
It is a purely mechanical process where the milk is forced (with very high pressure and often heat) to go through tiny tubes or mesh grills. This breaks up large fat globules and evens the consistency of the milk. This stops it forming layers with cream rising to the top, as you often read about in farms in older books. This process also allows extra cream/fat to be removed from the milk in order to create skim and lite milk with reduced fat content.
Raw milk advocates loudly proclaim that this is not a necessary process. In some ways they are correct. The cream can be siphoned off the top, as has been tradition, or drunk with it slightly separated. However, large-scale milk processors far prefer homogenisation because it ensures a consistency between milk of different herds and also makes it far easier to separate the different milk types.
So pasteurisation kills disease-carrying bacteria and homogenisation gives the milk a smooth and nice consistency!