Take home message
- Around 1860: Louis Pasteur advocated thermisation rather than pasteurisation of liquids in order to preserve the character of the product. If only we had listened to him.
- Around 1940: Lady Balfour saw milk pasteurisation as a necessary measure to combat the tuberculosis bacterium in milk. She advocated a temporary measure around World War II, but saw the prevention of TB infection in raw milk and cows as the most important measure.
- Around 1950: Experiments with the production of so called ‘model milk’ (grade A certified raw milk’ were conducted in the Netherlands and other countries with their own legislation.
- After 2000: Heating to 60oC is important in order not to alter the character of raw milk too much, especially in terms of immunological outcomes.
- In 2025: Increased knowledge and hygiene during milk production and storage have led to raw milk also being produced safely. However, in life 100% safety does not exist.
Louis Pasteur and heating
The concept of “pasteurisation” is attributed to Louis Pasteur (1822-1895), although as early as the beginning of the 19th century, there were people who advocated heating milk to make it safe for consumption (Westhoff, 1978). Nowadays, milk is heated before consumption almost everywhere. The combination of temperature and time determines whether a product has been heated sufficiently to be classified as safe. For example, at start pasteurisation of milk was at 63 oC for 30 minutes (vat or batch pasteurisation), later 72 oC for 15 seconds (HTST = High Temperature Short Time) (fig. 1).
Pasteurisation of milk has two objectives: (a) to extend the shelf life of raw milk by killing lactic acid-building bacteria, classically referred to as “delaying spoilage”, and (b) to make milk safe by killing pathogens. Pasteurisation was promoted for both purposes from the end of the 19th century onwards, because the germ counts in raw cow’s milk were very high and there was contamination among cows and humans with tuberculosis (TB), with high mortality rates, especially among children. TB (and also brucellosis) has now been virtually eradicated in Western Europe. The incidence of the disease (= number of new cases per 100,000 inhabitants) is low and usually comes from people arriving from abroad.
Fig 1. The combination of time (here in log 10 seconds) and temperature (in oC) determines whether a product is pasteurised. At 72 oC 10 seconds, at 63 oC 1800 seconds = 30 minutes)
Killing the tuberculosis bacterium
Jenkins et al., (1927) investigated whether milk infected with TB bacteria, when heated, is still capable of killing a guinea pig. Guinea pigs were used as test animals because of their susceptibility to TB. Milk heated to 53, 55 and 57.5 °C (for 30 minutes) still contained live TB bacteria and all guinea pigs became infected and died within six weeks. TB milk heated to 60 and 62.8 °C (= 145 °F) for 30 minutes is no longer dangerous to the guinea pigs and all survived. However, it must be ensured that all the milk in the vat has reached this final temperature, which is only possible if the milk is stirred continuously during heating. If parts of the milk remain too cold, i.e. below 58 °C, there is a risk that the TB bacteria will survive.
The WHO keeps track of how many new cases of TB are reported in countries worldwide. For the period 2021-2023, for example, this amounts to 4.3 cases per 100,000 inhabitants in the Netherlands. If you divide Europe into Western European countries and Eastern European plus former Soviet states, the average incidence is 5.8 and 18.7 per 100,000 respectively (derived from RIVM, 2025_Country List Tuberculosis). Deaths from TB no longer occur due to the eradication of the bacterium in Western countries and knowledge about the treatment of infected patients. This was different in the second half of the 19th century (Fig. 2).
Fig. 2. The steady decline in the number of deaths from tuberculosis from 1850 to 1970 in England and Wales combined (McKeown, 2016).
Figure 2 shows the number of deaths from TB (for England and Wales combined). It is clear that from the mid-19th century, when data on disease and mortality began to be systematically collected, the number of people dying from TB fell by approximately 25 per 100,000 inhabitants every 10 years, finally reaching zero around 1970. Long before the introduction of milk pasteurisation, mortality from TB was already declining. There is no break in the downward trend when pasteurisation was introduced in large English cities (around 1920-1930). The downward trend continued along the same line. Nevertheless, it cannot be denied that the introduction of pasteurisation contributed to the reduction in infant mortality at the end of the 19th and beginning of the 20th centuries.
Reducing the germ count
At the end of the 19th century, reducing the bacterial count through heating was an important commercial issue. Raw milk could sometimes smell sour upon delivery. Numerous experiments were conducted to establish regulations and recommendations on the best temperature to heat the milk. Insufficient heating resulted in only a limited increase in shelf life, while excessive heating was much more expensive and caused an undesirable change in taste (cooked milk taste).
Fig. 3. The percentage of the total number of bacteria (TPC) killed at increasing temperatures (heating for 30 minutes), derived from Jenkins, 1926.
Jenkins (1926) conducted a series of experiments in which raw milk of varying quality was heated to temperatures between 59 and 63 °C (30 minutes). Rising temperatures from 60 °C onwards kill more and more bacteria, up to a maximum of around 95% of the total (Fig. 3). Pasteurisation (62-63 °C) does not kill 100% of the bacteria, but it does achieve the most important goal of significantly reducing bacterial life in the milk. At a slightly lower temperature of around 60 °C, thermisation occurs; more bacteria remain alive.
Thermisation or pasteurisation of (cheese) milk
Nowadays, the question of “thermisation” or “pasteurisation” also plays a role in the labelling of Gouda cheese. When is a cheese considered “farm house raw milk cheese”, and when should it be labelled “pasteurised cheese”? Thanks to improved hygiene on farms and during milking, as well as closed milking systems, we no longer have to deal with the bacterial counts that were common at the beginning of the 20th century. In Jenkins’ experiments mentioned above, which involved heating experiments, the average germ count of raw milk in 1926 was 82,000 germs per ml. Milk, as used today for raw milk consumption, is well below 10,000, often even below 5,000 germs/ml. If we take the pasteurisation impact in 1926 as an example (95% germ reduction), pasteurisation results in a reduction from 82,000 to 4,000 germs/ml, not much less than well-produced modern hygienic raw milk in 2025.
Pasteurisation is therefore a measure to compensate for poor hygiene on a farm, resulting in a too high number of bacteria in raw milk. Pasteur came more from a knowledge of beer and wine, but advocated thermisation in order to preserve the taste and character of the raw product. He experimented and proposed the use of relatively low temperatures (50-60 °C), which were sufficient to destroy perishable organisms (in wine and later beer), but low enough not to alter the original properties of the drink (Westhoff, 1978). Thermisation is also used in milk processing. In large factories, milk may need to be stored for longer before further processing into a final product, and the milk can be thermised, cooled and stored again. On the farm, thermisation of cheese milk is used to deal a severe blow to certain bacteria, without there being any evidence of pasteurisation. The legal definition for pasteurisation is the absence of the enzyme alkaline phosphatase, becoming inactive by heating. With thermisation, this is not demonstrably the case, but the bacterial count is reduced. Thermisation is used as an auxiliary step on the farm with less consequences for the taste of the cheese itself. Many raw milk farmhouse cheese makers donot accept thermisation under the label of a raw milk cheese. They believe that those who use thermisation are cheating when it comes to the true meaning of the term “raw milk cheese”.
Immunological changes around 60°C?
It is important to note that the temperature choice around 60°C also affects the immunological quality of the (raw) milk. It may seem like a small difference whether you heat the milk to 60 °C or 63 °C for 10-30 minutes. However, the limit of 60 °C seems crucial for preserving the properties associated with raw milk.
Various studies show (Figs. 4-5) that heating to around 60 °C causes certain changes in the milk. Mice do not have an allergic reaction to raw milk that has been heated to 50 or 60 °C, but they do have a reaction after the milk was heated to 65 °C or higher (Fig. 4). When you look at in vitro research with the most important whey protein, beta-lactoglobulin (BLG), you see that the immune response hardly changes up to 60 °C compared to raw milk, but between 60 and 80 °C it rises steeply (fig. 5). Heating milk above 60 °C therefore results in an increased immunological response. The change in BLG immunoreactivity is an indication of this, but other heat-sensitive whey proteins probably also play a role here.
Fig 4. Allergic reaction after gradual heating of milk can be divided into two areas: up to 60 oC (green: thermisation) and above 65 oC (red: pasteurisation).
Fig 5. Increasing heating of the whey protein Beta-Lactoglobulin (BLG) and immunoreactivity in vitro: up to 60 oC there is a slight increase, above that (60 to 80 oC) there is a sharp increase in immunoreactivity. Highly heated BLG (‘boiled milk’) loses its immunological properties.
Were Louis Pasteur and Lady Eve Balfour right?
Pasteur focused on the taste and shelf life of the raw product (in the 1860s) and advocated low heating temperatures for beer and wine (Westhoff, 1978). Not pasteurisation, but thermisation. Lady Eve Balfour, as chair of the Soil Association, was willing to accept pasteurisation of raw milk (around the Second World War) as a temporary measure at a time when tuberculosis was present among cows and humans. TB (and most other infectious diseases) has now been curbed (read: eradicated) to such an extent that an important reason for pasteurising milk has disappeared. Knowledge about farm hygiene, milk cooling, the safety of raw milk and subclinical mastitis in cows is now so advanced that modern raw milk is generally as safe for consumption as raw milk (Berge and Baars, 2020). This certainly applies to those farmers that pay extra attention to the production of their raw milk, for example the German Vorzugsmilch, the English dairy farmers affiliated with the RMPA (Raw Milk Producers Association) or the American farms affiliated with RAWMI (Raw Milk Institute). These companies know what they are doing, maintain strict process control and have a well-established hygiene protocol. Even for new zoonotic problems, such as STEC, the hygiene measures at such companies seem to be sufficient to be able to supply extremely safe raw milk.
It has been a long road in terms of knowledge, technology and control, but it is possible: safe raw milk production and consumption. Now all that remains is acceptance.
Literature
- Abbring, S., Xiong, L., Diks, M. A., Baars, T., Garssen, J., Hettinga, K., & van Esch, B. C. (2020). Loss of allergy-protective capacity of raw cow’s milk after heat treatment coincides with loss of immunologically active whey proteins. Food & function, 11(6), 4982-4993.
- Berge, A. C., & Baars, T. (2020). Raw milk producers with high levels of hygiene and safety. Epidemiology & Infection, 148.
- Jenkins, H. (1926). Experiments on the pasteurisation of milk, with reference to the efficiency of commercial pasteurisation. Epidemiology & Infection, 25(3), 273-284.
- Karamonová, L., Fukal, L., Kodíček, M., Rauch, P., Mills, E. C., & Morgan 1, M. R. (2003). Immunoprobes for thermally-induced alterations in whey protein structure and their application to the analysis of thermally-treated milks. Food and agricultural immunology, 15(2), 77-91.
- McKeown, T. (2016). Determinants of Health. In Understanding and applying medical anthropology (pp. 99-104). Routledge.
- Westhoff, D. C. (1978). Heating milk for microbial destruction: A historical outline and update. Journal of Food Protection, 41(2), 122-130.
