processing methods

by nutritionist Maxine Sheils BSc (Hons) 

In part 1 of our dairy series, we delved into the differences between organic and non-organic cow’s milk, explored different forms of dairy intolerance and looked at the differences in plant-based milk alternatives. The second part of this series will explore the different forms of dairy processing including pasteurisation, homogenisation and the pros and cons of raw milk.  

Where does milk come from? Whilst we would like to think that the local farmer has personally milked Daisy the cow, with the milk going straight from the udder, into a bucket and then into the lovely glass-bottled milk that ends up on the doorstep, this is not an accurate reflection of reality. Smaller farms may still milk by hand but most farms automate the process, using a milking machine which pumps the milk directly into a tank where it is cooled. It is interesting to note that there is practically no bacteria in milk produced from a healthy cow; sources of contamination can occur, however, including mastitis (udder infection), passage from blood to milk, faecal and skin contamination and environmental sources, bringing us on to the use of pasteurisation.  

Remember your history lessons? Louis Pasteur invented the process of pasteurisation during the nineteenth century for the use of beer and wine. He discovered that heating food would kill many of the bacteria present and therefore prolong what we nowadays call ‘shelf life’. For milk, this process allows you to purchase dairy products to keep it in your fridge for up to a week without risk of spoilage. There are many ways to pasteurise milk but the most commonly used practice is to heat the milk to 72 degrees celsius for 15 seconds, with UHT milk being subjected to temperatures as high as 150 degrees Celsius for up to 15 seconds to allow a longer shelf-life.

Pasteurising milk eliminated many sources of illness in the early 1900s, such as typhoid fever, scarlet fever and diphtheria, but is this still necessary today? There is an increasing trend towards the consumption of raw milk with claimed benefits including more bioactive components, live enzymes including lactase which helps with the breakdown of milk, and beneficial bacteria that is otherwise destroyed during pasteurisation. Whilst these definitely appear to be attractive properties, it leaves the everyday dairy consumer confused about what the best and safest form of milk is, and made more difficult by the rules on distributing raw milk. If relying on purchasing your dairy produce from the supermarket, you will be restricted to pasteurised milk as producers of raw milk must supply it directly to consumers and not via a distributor – e.g. a shop. So let’s look at some of the health claims of raw milk in more detail before you decide whether to source and travel to your local raw milk distributor.  

1. Raw milk is more nutritious?

One of the arguments against pasteurisation is the nutritional value of raw milk, with many believing that there is a loss of nutrients once it is subject to heat. Whilst many nutrients withstand the heating process, one review focusing on the risks and benefits of milk pasteurisation suggests that levels of vitamin B1, B6, B9, B12 and vitamin C are reduced (although marginally), with trace minerals shown to remain unchanged (1); however, another review focusing on the effects of milk pasteurisation on vitamins confirmed that pasteurisation reduces the content of vitamins E, C, B2 and B12 as well as folate, but increased vitamin A.(2) Whilst milk does contain many vitamins it’s not a predominant source of these vitamins in the diet, except for vitamin B2.

2. Raw milk is anti-microbial

It is argued that raw milk contains enzymes and proteins that have antimicrobial properties and support immune function but that they are lost during pasteurisation. Studies suggest that these antimicrobial properties are, in fact, mainly present in colostrum (the first secretions from an animal during pregnancy, prior to birth and present in early milk), and naturally deplete throughout the lactation period. Therefore, unless you can ensure that your milk comes directly from a cow producing colostrum, you may not benefit from the antimicrobial properties in raw milk. Furthermore, if you do manage to purchase colostrum, these antimicrobial properties are believed to become inactive from refrigeration and therefore reduce your chances of benefitting from these properties (1).

3. Raw milk inhibits the growth of bacteria

Raw milk contains commensal lactic acid, which naturally inhibits the multiplication of bacteria; however, it would need to be stored at room temperature to retain this benefit,thus promoting the fast degradation of the quality of the milk. Whilst pasteurisation removes the commensal lactic acid allowing bacterial spores to grow, sterilised and UHT milk is considered sterile, and therefore no longer contain bacteria (1).

4. Raw milk is a source of probiotics

Raw milk contains probiotic strains, important bacteria which feed the microorganisms of the digestive tract, promoting health. While this sounds like another great reason to consume raw milk rather than pasteurised, the levels of probiotic strains are low in numbers and destroyed in intestinal transit, thereby rendering them ineffective (1).

5. Raw milk is better for those with lactose intolerance

Many people believe that drinking raw milk is a great way to counteract symptoms associated with lactose intolerance, however, the lactose content of milk is considered to have a similar level in both raw and pasteurised milk. For this reason, those intolerant to lactose should not be affected differently by raw or pasteurised milk as they both contain lactose (1). Whilst raw milk contains lactic acid bacteria, which can produce lactase (an enzyme which assists in the breakdown of the lactose content, as mentioned above), the benefits of lactic acid are limited by refrigeration. While there are no studies to confirm the positive effect of raw milk on lactose intolerance, the inclusion of Lactobacillus acidophilus to milk has been shown to aid digestion for those with lactose intolerance (2). Fermented milk products such as yoghurt, kefir and fermented cheese may be better tolerated as they also contain lactase.

6. Raw milk prevents allergies from developing

It has been suggested that the consumption of raw milk from a young age reduces the risk of developing immune and allergic conditions including hay fever and asthma. This is considered to be due to the increased exposure to pathogens, i.e. the bacteria present in raw milk, leading to a stronger development of the immune system. Whilst this suggestion stems from the hygiene hypothesis, the idea that people have reduced immunity as they are not exposed to germs and infections at a younger age, it is difficult to conclude that raw milk consumption alone is the reason for a potentially stronger immune system. Those children who are likely to consume raw milk from a younger age may also have a higher exposure to a farming environment and animals, which may all be factors in increasing exposure to bacteria.

So pasteurised milk is better than raw milk?

From reviewing these points, it appears that refrigeration of raw milk inhibits many of the beneficial properties of raw milk consumption – inactivation of enzymes and proteins, the inhibition of commensal lactic acid and of probiotic growth. Refrigeration of milk is important as it prevents rapid degradation of the quality, but does this mean that we should be consuming pasteurised milk? Going back to the reason why we pasteurise milk, i.e. to kill bacteria, by applying the hygiene hypothesis, one might infer that a bit of bacteria isn’t so bad. 

The potentially pathogenic micro-organisms of most concern within the UK when consuming raw milk are Campylobacter spp., Salmonella spp. and E.coli. These pathogenic organisms have an occurrence rate of 0-6% in raw milk, with a rate of 5, 18 and 13 respectively reported outbreaks in Europe, between 1970 and 2010, whilst pasteurised milk on the other hand, is considered sterile, and therefore free from pathogens. While raw milk certainly had higher associated risk factors in the past (i.e. tuberculosis during the 1950s), can we really compare the processing of raw milk then, to the hygiene standards applied now? One would expect the environment for milking to be much more hygienic now, with all equipment regularly sterilised. To add further value to this, there are very strict rules for the production of raw milk. For example, the cows must be healthy and free from tuberculosis and brucellosis, compliance to hygiene rules are inspected twice a year with produce sampled to ensure they comply with the microbiological standards set by Dairy Hygiene Inspectors. In 2014, the Advisory Committee on the Microbiological Safety of Food (ACMSF) reported that there have been no outbreaks of disease since 2003 as a result of consumption of raw dairy milk, likely due to these strict rules. Is it therefore correct to assume that consuming raw milk is really that risky?

Pasteurisation of milk also amends the flavour, reducing the ‘fresh milk flavour’ you would experience from a glass of raw milk. As the fat content of commercial milk is standardised to around 3.5%, which is slightly lower than that of fresh raw milk (4%), the perceived taste of milk is again negatively affected as a consequence.  

What about homogenisation?

Homogenisation is another form of dairy processing, with the aim of preventing the creaming effect of milk by reducing the size of the fat globules from roughly 3.5µm to below 1µm in diameter. This leads to a reduction in the cream-line formation that used to be a lot more common, gives the milk a whiter appearance, and is believed to provide a fuller-bodied flavour. Homogenisation also reduces the sensitivity of the milk to fat oxidation, leading to a longer shelf life; however, as the smaller fat globules are no longer covered by the original membrane, the milk becomes more sensitive to light, which can in turn reduce the nutritional quality and also reduce shelf life.

During the 1970s, it was suggested that homogenised milk caused atherosclerosis due to the body’s inability to break down the enzyme xanthine oxidase found in homogenised milk, thus leading to damage of the cardiovascular tissue. A review conducted in 1983 concluded that there is no evidence to confirm that homogenisation is linked to atherosclerosis, although the topic continues to provoke debate to this day, with researchers suggesting more studies are required to establish whether homogenised milk is indeed pro-atherogenic or may have any other health implications. (3, 4, 6) In the meantime, it should be noted that the homogenisation of milk appears to lead to easier absorption of fat, with studies finding a benefit where homogenising mother’s milk helps to increase fat absorption in babies with very low birth weight. (5)  

To buy raw milk or processed milk

There are many factors to consider when deciding what form you would like your milk to come in. Whilst raw milk may contain many beneficial properties, how much they benefit the consumer has yet to be confirmed in clinical practice, but this does not necessarily negate the anecdotal ‘evidence’ of the many consumers and advocates of raw milk. Is pasteurisation and homogenisation just another unnecessary step of processing food and making it less similar to the original form?  

There are many farms offering raw milk so if you do decide to make the switch, ensure you purchase it from a reputable farm. Caution is also recommended when providing raw milk to those at greater risk from infection, including babies and children, the elderly, pregnant women and those with compromised immunity. Whilst you can purchase non-pasteurised homogenised milk, when it comes to making a decision on homogenisation, unless you are trying to increase your fat absorption, it probably does come down to taste and preference of consuming a totally natural food rather than a processed food.

If you do choose to consume pasteurised milk rather than raw milk, you should consider increasing your dietary sources of vitamin B2 with foods such as spinach, eggs, asparagus, almonds and mushrooms, or consider a vitamin B2 supplement. Igennus Healthcare Nutrition recommends vitamin B2 to be in riboflavin-5-phosphate form as this is the active form, ready to be utilised by the body.  


  1.  Claeys W. L., Cardoen S., Daube G., et al. (2013). ‘Raw or heated cow milk consumption: Review of risks and benefits’, Food Control, 31, pp. 251-262.
  2. Macdonald L. E., Brett J., Kelton D., et al. (2011). ‘A systematic review and meta-analysis of the effects of pasteurization on milk vitamins, and evidence for raw milk consumption and other health-related outcomes’, Journal of food protection, 74 (11), pp. 1814-1832.
  3. Clifford A. J., Ho C. Y., & Swenerton H. (1983). ‘Homogenized bovine milk xanthine oxidase: a critique of the hypothesis relating to plasmalogen depletion and cardiovascular disease’, The American journal of clinical nutrition, 38 (2), pp. 327-332.
  4. Michalski M. S., & Januel C. (2006). ‘Does homogenization affect the human health properties of cow’s milk?’, Trends in food science and technology, 17 (8), pp. 423 – 437.
  5. Michalski M. C. (2006). ‘On the supposed influence of milk homogenization on the risk of CVD, diabetes and allergy’, British journal of nutrition, 97 (4), pp. 598-610.
  6. Thomaz A. C. P., Goncalves A. L. & Martinez F. E. (1999). ‘Effects of human milk homogenization on fat absorption in very low birth weight infants’, Nutrition research, 19 (4), pp. 483-492.

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