Fact or Fiction – Safety and Health of Raw Milk

I apologize to my regular readers for this unusual post. This is a planned post, as part of my fermented food series. It was supposed to follow another of my hard-core microbiology experiments, but I’ve needed this resource elsewhere so I’m writing it about a dozen articles early.

This article is going to take a historical and scientific look at the use and safety of raw (unpasturized) milk – something worth thinking about when considering making fermented milk products such as yoghurt or cheese. I’ve included extensive links to my sources throughout this article, so please check those out before accusing me of being a shill for the pasteurization industry.

This post going to be a long one, so here’s an index for those who want to jump around:

  1. What is Raw Milk
  2. Myths and Claims About Raw Milk
  3. A (Brief) History of Milk Consumption & Fermented Milk Foods
  4. A Microbiological & Epidemiological Look at Raw Milk
  5. Being as Safe as You Can
  6. Conclusions

What is Raw Milk

Raw milk is simply milk that has not been pasteurized – e.g. has been taken directly from an animal, and then sold (or used) without any treatment to reduce bacterial or fungal contamination. Because of this, raw milk contains more bacteria than pasteurized milk.

I’ve written about pasteurization before. In short, pasteurization relies on heating a food item to a temperature, for long enough a time, to reduce the bacterial counts to below 100 colony forming units per mL (CFU/mL). Note: 1 CFU = 1 viable bacterial cell. Most pasteurization processes reduce bacterial counts well below this point – typically to 30 CFU/mL or lower. In comparison, high-quality raw milk is defined as raw milk containing under 10,000 CFU/mL. It’s not uncommon in unregulated markets (e.g. USA and Canada) for raw milk to start with over 10,000,000 CFU/ml!

That may sound scary, but is it really? The answer is…complicated. I’ll address this in detail more below, but the short version is that the risk of milk containing a pathogen scales with CFU’s. So as pasteurized milk contains very few bacteria it is therefore unlikely to have pathogens, while both the number of bacteria and risk of pathogens increases in high-quality raw milk, and increases even further in lower-quality raw milk. In other words, its a sliding scale or risk, rather than an absolute safe versus not-safe situation.

The difference between low- and high-quality raw milk is largely driven by how milk is collected and monitored. In countries with a regulated raw milk industry (e.g. France) there are strict rules on animal health (e.g. monitoring for mastitis and gastroenteritis prior to milking), milking procedures (e.g. milking machine and udder sanitation, milk room cleanliness standards, etc), milk storage (e.g. how quickly milk must be cooled, and to what temperatures), and active monitoring of the milk supply for pathogens. This allows much of the risk of raw milk to be mitigated. They also have a traceable milk system, allowing infections to be traced back to the farm, and actions taken to identify and correct the cause of the contamination.

A methylene blue test, used to test the safety of milk. A blue dye is added to the milk. Bacteria will reduce the dye to a colourless state. The time it takes for the milk to go colourless is used to determine its safety. In this example, I've compared commercial pasteurized cows milk (left) to home-pasteurized and raw goats milk (middle and right). This is the colour change after 6 hours, which indicates that our raw milk is of high-quality.
A methylene blue test used to test the safety of milk. A blue dye is added to the milk. Bacteria will reduce the dye to a colourless state. The time it takes for the milk to go from blue to white is used to determine its safety. In this example, I’ve compared commercial pasteurized cows milk (left) to home-pasteurized and raw goats milk (middle and right). The colour change in the raw milk took 8 hours, indicating that the milk is of high quality.

Lower-quality milk is common in unregulated/illegal raw milk markets (e.g. the USA and Canada). Because there are minimal or no regulations, there are few or no standards protecting the raw milk supply. In many cases even the tools needed to ensure a safe supply are hard or impossible to come by. In the case of Canada where sale it outright illegal, there are often active attempts to evade detection and monitoring. As you can imagine, in these markets the quality of milk can vary hugely. Some producers will take the same care and diligence in ensuring a quality supply as farmers in regulated systems. Other will not, with a corresponding increase in the risk of contamination.

But even those taking the utmost care in unregulated systems simply cannot achieve the same quality as those in regulated systems. This is largely due to “invisible” contamination, such as that coming from a low-grade mastitis. While the animal is not obviously ill, the milk will be contaminated with the bacteria causing the mastitis. In regulated industries, these low-grade infections are detected in milk plants using specialized assays for detecting bacteria. Few*, if any milk producers in unregulated markets will have access to the tools to do this themselves.

*my usual readers will be unsurprised to learn that I do this testing on my farm’s milk (see image above).

As for pasteurization itself, the process is fairly simple, but can be conducted in a few ways. The information below is generally true for Canadian provinces (each regulates pasteurization individually, so there are some minor variances), and international standards are virtually identical. There are different approaches, but the generally accepted guidelines are:

  1. Bulk pasteurization: Solely used by people at home. Heat a bulk supply of milk to a temperature of at least 63°C/145F. This is maintained for not less than 30 minutes.
  2. Flash Pasteurization: This is how most milk is pasteurized. Milk is run through a narrow tube through a heat supply. This quickly heats the milk to a temperature of at least 72°C/161F for at least 25 seconds. The milk is then rapidly cooled.
  3. Ultra High Temperature Pasteurization: Milk is passed through a tube at high pressure and rapidly heated to 135 C. This temperature is held for at least 2 seconds before the milk is rapidly cooled. This effectively sterilized the milk, allowing it to be stored at room temperature until opened.
  4. Ultra Filtration: Rather than heating the milk, it is instead filtered through a 0.2 micron filter. This is used for some high-end milks, but is more expensive than pasteurization. It can also be difficult to perform with full-fat milk.

Raw Milk Myths

There are a number of myths – both in favour and in opposition to – raw milk consumption. I can’t cover them all, but I will do my best to cover the major claims. As always, I will provide links to the studies I’ve based my “myth busting” on.

Myth 1: Raw milk tastes better. It is often claimed that pasteurization changes milk’s flavour or texture. But is there a difference?

This is a difficult question to answer, as many things can contribute to our perception of flavour and texture. This includes factors such as personal biases, packaging, and even the location where the tests are run. These confounding factors can cause people to perceive differences where none exist…or to miss otherwise obvious differences. Luckily, a German research group did a well designed experiment comparing UHT, pasteurized, pasteurized organic, and raw milk. Importantly, they compared the same peoples perceptions of these different milks first blinded (meaning the subjects did not know anything about the source of the milk they were tasting), and then repeated the tests with the same people unblinded (meaning the subjects knew what milk they were drinking). What they found is quite interesting:

  1. Blinded participants (e.g. the participants didn’t know which milk they were tasting) rated all of the milks, except for UHT milk, equally. The UHT milk was rated slightly lower than the others. That’s right – if someone didn’t know the source of the milk, they rated pasteurized, pasteurized organic, and raw milk to be equally good.
  2. But when the same participants weren’t blinded, and were fully knowledgeable of where the milk came from, everything changed. In this case organic pasteurized and raw milk were rated higher, while the UHT and pasteurized milk were rated lower.

In other words, the claimed differences in milk flavour (UHT aside) is entirely in peoples heads.

Another claim is that raw milk cheese also tasted better (or, at least, different). That is a more complex topic, which I will cover in a later post.

Myth 2: Pasteurized Milk Looses Nutrition. This is another of those pernicious myths. This is also an easy question to address, as modern technologies can detect literally one part per billion changes in these compounds. In simple terms, milk can be thought to have five major nutrient groups – proteins, lipids/fats, vitamins, trace metals, and sugars.

The first, protein, is very minimally affected by pasteurization. Proteins themselves are comprised of 20 different amino acids that are strung together in specific sequences to create functional proteins. Of these 20 amino acids, 19 are unaffected by pasteurization, while one – lysine – decreases by 1-4% in concentration. Lysine itself makes up ~5.5% of the amino acids in animal proteins, meaning that the total protein content of milk changes by 0.055% to 0.22%. This is roughly the amount protein content varies with seasonal changes in milk. In the context of your nutritional needs, this change is meaningless – its the equivalent to less than a teaspoon difference in your daily milk consumption.

The second, lipids and fats, are simply not affected by pasteurization (see page 416). In contrast, milk fat content varies greatly with seasonal and dietary changes. Commercial milk tends to be standardized to specific fat/lipid contents, so this doesn’t affect consumers much. But if you are producing your own milk, or buying direct from a farm, you will encounter these seasonal changes in fat content.

The third, vitamins, is of course a large group of nutrients. Even with UHT, no changes are seen in the amount of the major milk vitamins.

The fourth, trace metals, includes calcium, but also other metals such as zinc and iron. As with vitamins, there are no detectable change in these compounds even after UHT treatment of milk. That said, it is worth noting that calcium does undergo some microcrystalization after pasteurization. Essentially, free calcium ions end up binding to compounds such as phosphate and come out of solution. These tiny crystals remain in suspension – and we digest them just fine – so there is no change in the nutrients provided to us by the milk.

For cheese makers this microcrystalization can be an issue, as that microcrystalized calcium cannot be used by enzymes such as rennet. Insufficient calcium will impede the setting of curd. This is why it is common practice to add a small amount of calcium chloride to milk during cheese making. It restores the soluble (non-crystalline) calcium content, allowing rennet to work. In the context of human nutrition, the addition of calcium chloride will produce a cheese with a slightly higher calcium content than one made without added calcium.

The final – sugars – is lactose. Lactose is a disaccharide: a sugar made of two simpler sugars connected together. Lactose is a very stable compound, and doesn’t degrade unless heated well above the boiling point of water. Meaning that you’d have to boil nearly all the water out of the milk before there would be any change in the lactose composition. This means that there is no change in the lactose composition of the milk, or in its digestablity.

To digest lactose our bodies first need to split the lactose into its component sugars, which is done by the intestinal enzyme lactase. All infants have lactase (so they can consume milk), but in most adults this activity is lost. This is why the majority of humans cannot consume milk unless it’s been processed to remove the lactose (e.g. through making cheese or yogourt). A few human populations evolved to retain lactase activity into adulthood, and it is only those people who can consume milk into adulthood.

Myth 3: Pasteurized milk lacks key enzymes. This is one of those myths which is true and irrelevant at the same time. While milk protein is mostly casein – a specialized protein that helps dissolve fat into the milk – a small portion of the protein are enzymes. The major enzymes are alkaline phosphatase, lactoperoxidase, lysozyme, lipase, and proteinases. Alkaline phosphatase removes phosphate groups from other chemicals, and helps to regulate the solubility of compounds in milk. Lactoperoxidase produces peroxides, which are antibacterial, while lysozyme punches holes in bacterial cells. Lipase degrades lipids, while proteinases break down proteins.

These latter three help young animals digest the milk. Of these, alkaline phosphatase is partially inactivated by pasteurization. In fact, the decrease in this enzymes activity is used as a measure to make sure that milk has been pasteurized properly. Lactoperoxidase and lysozyme are unaffected by pasteurization. There are multiple lipases and proteinases, and the effect of pasteurization on these vary. Generally, lipases are more sensitive to pasteurization than proteinases.

So there are differences in the activity of some enzymes in milk…but this is also irrelevant from the perspective humans over the age of 2. The reason this is irrelevant is that our stomachs efficiently degrade proteins, meaning the active enzymes are destroyed before entering your intestinal tract. It is worth noting that until over the age of 1 infants have weaker protein-degrading capacity. Which is why these enzymes are in milk – to aid the infants. But, because of this, you should also never give animal milk to an infant as the active enzymes may have deleterious effects.

Coming back to cheesemaking, the inactivation of lipases by pasteurization may require that additional lipase be added to a cheese if the flavour provided by lipase is desired. Luckily, lipase powder is cheap and readily available.

Myth 4: Raw milk protects against lactose intolerance. Lactose persistence (the ability to consume lactose into adulthood) is a genetic trait determined by a well known and understood genetic mechanism. This mechanism is not affected by the things we eat. It’s a hard-wired genetic trait, as immutable as the colour of your eyes.

Myth 5: Raw milk protects against milk allergy (or allergies in general): This one is based on a tiny nugget of truth, but ignores the bigger picture. There are a few studies which have shown that people who consume raw milk have fewer allergies. Seems like a slam-dunk, doesn’t it? But these studies forgot to do one key thing – to address confounders. Confounders, in simple terms, are other factors that may account for the results. In the case of these studies, that confounder was where the people lived. Raw milk consumers were almost exclusively rural residents who lived on farms, while pasteurized milk consumers were almost entirely urban dwellers. Studies have since shown that raw milk has nothing to do with the rates of allergies. Rather, its living in a rural environment that is protective (example 1, 2, 3).

Myth 6: Raw milk is almost certainty deadly. Most of the myths I’ve tackled up to this point are ones spread by raw milk proponents. But they’re not the only ones guilty of using hyperbole to argue their case. It is not uncommon to see raw milk treated as though all of it was dangerous. That any consumption is taking your life into your own hands. There is an increased risk to consuming raw milk compared to pasteurized milk, which I’ll discuss in detail below, but while there is an increased risk, it is not an universal risk. This is milk we’re talking about here, not cyanide.

Myth 7: Raw milk is probiotic. I’ve written about probiotics before, so I’m not going to rehash everything again. As a quick reminder, a probiotic is a living microorganism, which when administered in sufficient numbers, has a beneficial effect on the host. While most probiotics are lactobacilli, most lactobacilli are not probiotics. Less than 1% of tested lactobacilli – and far, far less than that of other genera of bacteria – have been found to have probiotic effects.

So the likelihood that random milk from a random animal has a probiotic effect is pretty small. But even if every bacterium in a bottle of raw milk is a probiotic, you’re still out of luck. Most probiotics have a minimum effective dose of over a billion bacterial cells per day, with >10 billion typically required. Quality raw milk contains around 10,000 bacteria per millilitre – meaning you’d have to drink about a thousand litres of raw milk a day to get a probiotic effect! And again, that’s making the absurd assumption that every bacteria in the milk is probiotic.

Myth 8: The dangers of milk are due to modern farming. This is also a common claim, but one which does not stand up to scrutiny of the historical record. In reality, unfermented milk was rarely consumed prior to the industrial age. Both classical and medieval cultures had a very negative view of the consumption of milk. Our image of a pastoral past, where farmers lived off of fresh milk from cows wandering the dells and hills of medieval and renaissance Europe, simply did not exist. This is a big topic, so the entirety of the next section is centred on this history.


A History of Milk Consumption & Fermented Milk Foods

Before I go into a detailed look at modern milk safety, its worth looking at how milk was consumed and perceived historically. Much of the rhetoric surrounding raw milk is based on misconceptions of how milk was used and perceived before modern times. Raw milk proponents often claim that consuming raw milk is a return to historical norms, while pasteurization advocates will point to the lethal milk of the Victoria era as an all-encompassing example of historical “reality”.

Both, of course, are wrong.

The history of milk consumption is actually two histories. The first is the story of the peoples of the Middle East, Europe and of the western Eurasian steppe. The second is of the peoples of western Africa. The details of the latter poorly studied, so I’m going to focus on Eurasian history.

Milk in Pre-History

Milk producing animals (goats and sheep) were first domesticated in the area round Iran sometime around 10,500 years ago. Aurochs (cattle) were domesticated in Anatolia soon thereafter. The farming of these animals spread quick quickly into southern Europe and the steppe, and it was shortly after this time that the lactase persistence gene evolved. As a reminder, this is the form of the lactase gene which allows us to consume lactose into adulthood. This timeline has led some to think this a simple story: some people domesticated milk animals and developed the genes to allow them to consume milk into adulthood, and then these people (or their genes and farming practices) spread across Eurasia.

But this is not what happened – the story is more complex and interesting than that! While farming and farm animals spread across Eurasia like wildfire, lactase persistance did not. As one example, sequencing of of skeletons in central Europe found that the lactase persistence gene arrived somewhere around 2500 BCE – five thousand years after animal agriculture arrived in the area, and four thousand years after the first unambiguous evidence of cheese making in the area. A recent study has found evidence that lactase persistence most likely spread during a period of frequent famine and disease, potentially as people with this trait could consume milk without aggravating diarrheal disease. Amazingly, the same study found that lactase persistence didn’t appear in most regions of Europe until between 1000 and 500 BCE!

In other words, Europeans found ways to remove the lactose from milk (and to preserve it) long before they developed the biochemistry needed to consume large amounts of lactose after infancy. It was thousands of years from when our ancestors figured out how to preserve milk and convert it into a consumable form, to when they received the genetic tools to consume milk itself. And this isn’t unique to Europe. In fact, today there are cultures where milk is a major source of nutrition despite these cultures’ people being entirely lactose intolerant. Genetic analysis of the organisms used to make cheese and yogourt show that the microbes we use to prepare these foods evolved as unique organisms around 10,000 years ago. That this microbial domestication occurs at the same time that animals were domesticated, but long before the genes for consuming milk were common, is not likely a coincidence.

In other words, we domesticated microorganisms which could remove the lactose from milk (and also preserve the milk as cheese, yoghurt, and related product), thousands of years before we had the capability to drink unprocessed milk.

The Classical Period

Fast-forward a few thousand years and we run into the first written record of milk consumption. This was in the form of cheese making, and was recorded by Homer in the Odyssey. By the Roman era cheese making was commonplace, and somewhat interestingly, so was a very strong bias against drinking milk. Romans derided the milk-drinking culture of Germanic and Celtic tribes. They were particularly aghast at the large volumes of “curdled milk” those barbarians would quaff. While the “barbarian” tribes didn’t leave written records of their own, Roman sources are clear that they consumed large amounts of curdled milk. We don’t know exactly what this was, but the fact it was curdled indicates that it was fermented, and likely something akin to yoghurt or kefir.

The Medieval Period

In the medieval period there was a strong link between a persons social class and the foods they would consume, with chroniclers diligently recording the foods “worth” of different classes. In some cases there are even recorded laws dictating what can be consumed, and by whom. As in the classical era, while fermented milk products (especially cheese) were central to the diet of medieval Europeans, milk was looked upon negatively. It was considered a food for the very poor and very sick. And even then, people were generally drinking whey or soured milk, rather than milk straight from an animal.

So for most of European history humans consumed fermented or cooked milk products, but not milk itself. Moreover, milk had generally negative connotations starting at least in the early Roman period if not before.

So when did this change?

The Modern Era

The widespread consumption of unfermented milk didn’t really take off until the mass urbanization of the industrial era that took place in the mid-1800’s. The need for a cheap protein source that could be easily transported by rail was the driver of this change. This also led to many issues. A mixture of poor storage and adulteration led to mass infection – largely of poor people – with several foodborne diseases. The worst of these was bovine tuberculosis, which killed an estimated 3,000 people a year in the city of London alone! Once this link had been established, laws mandating that all milk be pasteurized became common place, with these laws first appearing in the early-1900’s.

TL:DR

From the start of human agriculture until ~200 years ago milk was generally not consumed unless fermented or cooked. It was considered an unsafe – and often uncouth – food. Drinking of milk is very much a modern development. It’s also a development which was fatal to hundreds of thousands of people until pasteurization became common.


A Microbiological & Epidemiological Look at Raw Milk

So that was a lot of writing to get to this point – a look at what recent scientific and epidemiological research tells us about modern raw milk.

The Microbiological Perspective

Don’t forget, the point of milk is to provide young animals with an energy and nutrient dense food source. Which means that bacteria also find it an energy and nutrient dense food source. We microbiologists often take advantage of this fact and use milk as part of microbial growth media. If you’ve ever had milk spoil you’ve experienced this growth first hand. But this fact alone doesn’t make milk dangerous. You can just as easily grow harmless bacteria in milk as you can pathogens.

The other thing to remember about milk is where it comes from – the udders of ruminants. Which are located below the anus of the animal, and we all know what comes out of there. The positioning of the udders under the anus may not even be accidental, with some studies identifying the fecal-udder-milk-calf transmission route to be critical for colonization of a calf’s intestinal tract with the proper microbiota. Whether this is something that evolved specifically for this purpose, or is a “happy accident” remains unclear. In either case, fecal bacteria are commonplace on the udders of milk animals, and indeed, makeup the majority of a healthy udders microbiota.

Risk from Resident Bacteria

This brings us to the first danger of raw milk. While these bacteria are a safe and critical part of the ruminants microbiota, we humans are not ruminants. Bacteria which are perfectly safe (and even necessary) in a cow can be deadly to us. As one example, E. coli O157:H7 is a common bacteria in the guts of cows. Here, it is a harmless and normal part of the cow’s microbiota. In us, it produces shigga toxin, leading to kidney failure and death in 2-7% of infected people. Fecal and udder-resident bacteria like E. coli are found in the majority of raw milk samples tested. Campylobacter is another kind of bacteria which can be transmitted in this fashion, and causes a food poisoning illness that lasts about a week. In some cases, long-term injury or illness can result.

Unfortunately, it is very difficult to control these bacteria at the level of a farm as they are normally present on the udder.

Risk from Animal Pathogens

The second danger of raw milk is infectious bacteria – as in bacteria which make both the animal, and people, ill. This includes some of the “scarier” foodborne bacteria including Listeria, Staphylococcus aureus, Salmonella sp., and Brucella.

Listeria is probably the most dangerous of these, and quite frighteningly, can even grow in refrigerated milk. It is the deadliest forms of food poisoning, on average killing 20% of infected people. Listeria is a master at invading and killing immune cells, allowing it to disseminate throughout the body.

Brucella is much less of a concern than it was historically, as it has been exterminated from cattle herds throughout much of the developed world. It does remain an occasional infectious agent amount sheep and goat herds. Brucella is rarely deadly, but it can cause vomiting, diarrhea, liver damage, and in some patients establish chronic infections that can lead to arthritis and other issues.

Staphylococcus aureus is the most common cause of mastitis (infection of the udder), and is also a common infection in humans. Staphylococcus can infect many tissues, causing everything from minor skin infections, through to lethal infection of bones and heart valves. When consumed orally (e.g. in milk) it can cause an acute (appearing in hours) and usually short-lived (hours to a few days) food poisoning. While unpleasant, this form of food poisoning rarely leads to severe complications or death.

Salmonella are, unfortunately, rather common. Salmonella also come in two major forms – non-invasive and invasive (the latter is also known as typhoid fever). Non-invasive Salmonella is probably the most common form of food poisoning among humans, accounting for most cases of “stomach flu” that people experience. Salmonella food poisoning is unpleasant, but rarely leads to sever complications or death. Invasive Salmonella is a much more dangerous disease, but thankfully this bacterium is almost unheard of throughout North American and Europe, while people tend to be vaccinated for this disease where this bacterium is common.

A critical note: For several of the diseases I wrote but rarely leads to sever complications or death. Some people tend to interpret this as meaning that they are harmless, but this is not the case. Infections put an immense burden on our bodies which have long-term consequences. The stress from a bout of food poisoning can accelerate the development of heart disease, promote cognitive decline, complicate diseases such as diabetes, and even causes some forms of cancer. So while you may survive the initial infection seemingly unscathed, your risk of developing oft-fatal diseases later in life has increased.

Because these bacteria also cause disease in farm animals, the risk they present to people is directly proportional to the attention and care a farmer puts into their animals. All of these produce signs of disease, meaning an observant farmer can avoid milking these animals. Signs of disease can vary depending on the organism, but most of these either produce diarrhea or mastitis (inflammation of the udder and teats). Never consume milk from a sick animal, even if it has been pasteurized.

The Epidemiological Perspective

The above section defines and describes the major pathogenic organisms that can be present in raw milk. These represent the hazards that are potentially present in raw milk. But what that section doesn’t tell you about is the likelihood of exposure to those bacteria. Risk is what we’re worried about, and is determined by a mixture of hazard and exposure. After all, a great white shark is a deadly hazard…but if you’re standing in a corn field in Iowa the risk to you is zero.

Complicating this part is the fact that risk is not consistent between regions due to regulatory differences, differences in enforcement, and the use of testing. I mentioned in the beginning that France has a very rigorous monitoring and safety program for their raw milk market. This makes their market one of the safest in the world. Canada represents the opposite of France, in that it does not allow raw milk sales or use outside of some very limited commercial cheese making applications. As all raw milk sales are illegal there is both a lack of a safety framework and deliberate attempts to avoid detection by the Canadian Food Inspection Agency. The USA falls somewhere in the middle and has a patchwork of regulations, ranging from no legal sales, to “farm gate” sales…but with no overarching regulatory or testing system like that in France. Thus, these three countries give us some very different “lenses” to use to look at risk.

France: The regulatory environment in France offers us an excellent opportunity to see what a well-regulated and safety-conscious raw milk industry looks like. ANSES (the French Agency for Food, Environmental and Occupational Health and Safety) recently performed a detailed analysis of the association of foodborne illness from raw milk cheeses over the decade spanning from 2008-2018. Note that these are outbreaks only – e.g. events that affected multiple people, not individual cases. I’ve summarized their findings below.

OrganismFrom Raw MilkOther/Unknown
E. coli64
Listeria1423
Salmonella1832

About half of those raw milk associated outbreaks were linked back to poor or failed hygienic practices. The remainder were not ascribed to an underlying cause. In either case, those numbers clearly show that raw milk cheese is a major source of foodborne illness in France. Unfortunately, while France is quite rigorous in regulating their raw milk industry, they don’t do a great job of tracking what portion of products sold are raw versus pasteurized. As such, while they have shown that 48.4% of outbreaks are from unpasteurized products (with an additional 20% of outbreaks from products with an unknown pasteurization status), we cannot easily convert that to risk. The NYT claims that 18% of milk products in France are unpasteurized (I couldn’t find verification of this). Assuming this is true, French raw milk products are 270 to 380 times more likely to cause foodborne illness than pasteurized products.

USA: A recent review by the CDC sought to assess risk, drawing from data recorded in the national database of foodborne illness. This was a more complex analysis that the one done in France, as in addition to looking at the number of outbreaks, the CDC also used population and consumer data to determine the risk to individuals who consume versus do not consume raw milk products. The findings are striking – 96% of foodborne illness caused by dairy products were caused by raw milk, despite raw milk representing only 3-5% of the total dairy market! In terms of relative risk, raw milk and raw milk products were 840 times more likely to cause foodborne illness than were pasteurized products.

Canada: That brings us to my home country of Canada – where, as a reminder, raw milk sales are illegal. This makes estimating risk extremely hard as researchers are tracking criminal activity. A recent study attempted to do just this. 62.5% of milk-product associated outbreaks identified in this study were due to unpasteurized products, and accounted for 78% of disease cases (e.g. raw milk outbreaks were both more common, and larger, than outbreaks from pasteurized products). Taking into account the estimated size of the Canadian raw milk industry (1.2% to 2.3% of total milk sales), this makes raw milk between 1,400 times and 2,600 times more dangerous that pasteurized products.

The Bigger Picture

Clearly regulation makes raw milk products safer. Raw milk products in France are up to ten times safer than they are in Canada, with the USA falling somewhere in the middle. But it is also clear that even with a rigorous regulatory and testing regime, raw milk remains significantly more dangerous than pasteurized products. In the broader context of food safety, raw milk is by most measures, the most dangerous food product consumed in the Western world on a per-serving basis.


Being Safe as You Can with Raw Milk

Pasteurizing is the best way to be safe when using milk products. But what can be done if you want to use raw milk, but don’t live in a country with a secured and regulated supply? The answer is “not much, unless you own your own animals”. Keep in mind, a trusted supplier only has to make a minor mistake for milk to become contaminated. If you own your own animals, you can collect raw milk in a manner which should produce a relatively safe product. For that matter, a lot of this advice is good for maintaining healthy and safe animals even if pasteurizing your milk.

Maintain healthy animals and a clean environment

This one is rather obvious, but still needs to be stated. Keep your barn (or wherever your animals live) as clean as you can. Feces and soiled bedding should be removed daily. Areas where the animals urinate should be allowed to dry completely each day, and if the area is sand or soil, the sand/soil replaced annually. Animals should be inspected before each milking for signs of disease, looking for things such as:

  1. Soiled rump, anal area, udder, or area between the hind legs. Inspect the barn for unusual feces (e.g. clumped feces in animals that normally produce pellets). This can be a sign of diarrheal or other intestinal disease.
  2. Sores on the teats or udder, or patches of hair loss on the udder. These are signs of cellulitis (bacterial skin infection).
  3. Red, swollen, or sensitive teats, or signs of solid material or blood in the first milk expelled when milking is started. All of these are signs of mastitis (infection of the mammary gland/udder).
  4. Lethargy, excessive coughing, poor eating, or general signs of malaise. All of these are general signs of infection.

Milk from animals showing these signs should never be consumed raw or pasteurized. Infected animals should be quarantined to limit the spread of disease throughout the herd, and if necessary, a veterinarian consulted to ensure proper treatment.

Milk Collection

While some contamination of raw milk occurs within the udder itself, contamination is also introduced during the milking process. This often occurs when debris fall into the milk as it is collected, or from bacteria on the skin of the teats. This risk can be mitigated fairly simply:

  1. Use a milking machine, rather than hand milking. Milking machines are closed systems, making it impossible for materials to fall into the milk once it leaves the animal. In contrast, hand-milking into an open container leaves the milk exposed to contaminants falling off of the animal, or from the environment.
  2. Pre-sanitize the milk collecting equipment before use. Contamination doesn’t just come from animals, it can also come from equipment. Sanitizing all parts of the milking machine that will contact milk will reduce this risk.
  3. Hand-strip the teats before milking and closely inspect the stripped milk. To hand-strip, manually milk a small amount of milk out of each teat onto a clean rag or shallow dish. Inspect the milk for white clumps or pink colourization. Animals showing either or both signs likely have mastitis. The milk from these animals is unsafe for consumption and should be discarded. Moreover, this milk should not be collected using equipment which will be used to collect milk for consumption (raw or pasteurized). Pre-stripping will also expel the milk closest to the duct, which is the milk most likely to be contaminated.
  4. Use a teat dip before milking. These contain skin-safe sanitizing agents which will reduce the number of potential contaminants on the teat. Teat dip should be used immediately before attaching the milking machine, but after hand-stripping.
  5. Chill the milk as it is collected. E.G. by placing the receiving container in an ice-bath.

After collection

Raw milk should be used quickly after collection as it is much less shelf-stable than pasteurized milk. Milk should be transferred from your milking machine to sanitized containers and chilled to 4C (39F) or cooler as quickly as possible after collection, and maintained at this temperature until used. Ideally, if making cheese, make the cheese the same day as the milk was collected. If you need multiple milking days to collect the milk for your planned batch size, make sure you are collecting this milk over the minimum time frame and that you make the cheese as soon as you have enough milk.

And most importantly, use your senses and dispose of any milk or milk product you think may have issues. Unusual colour, texture, or aroma may be a sign of contamination – if in doubt, throw it out!


Conclusions

I think at this point the conclusions are obvious, but are worth stating in a clear form:

  1. There is no meaningful nutritional, gastronomic (flavour/aroma), or health benefits to consuming raw milk compared to conventionally pasteurized milk.
  2. There is no meaningful nutritional differences between raw milk and pasteurized milk – not even with UHT pasteurized milk.
  3. Raw milk is much more likely to cause foodborne illness than is pasteurized milk.
  4. While regulations and good practices can reduce the risk presented by raw milk products, they cannot eliminate this risk.
  5. Pasteurization is a simple method of eliminating most of the risks present in raw milk.

10 thoughts on “Fact or Fiction – Safety and Health of Raw Milk

  • August 10, 2022 at 1:39 pm
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    Thank you for this interesting article! I started my fermentation adventure with yoghurt, fermented vegetables etc. The first book about fermentation I read was from Sandor Katz (The Art of Fermentatation). Not sure what you think about this book. He is of course no biologist so I’m interested in your opinion. In his book he writes about “Clabber”. I successfully made Clabber according to his instructions and I liked it. I bought raw milk (here in Switzerland you can buy it in the organic super market) and I just let it ferment at room temperature. It got sour but in a pleasant way. Do you consider this to be “safe”? My thoughts were (up to now 🙂 ): The laco bacillus lower the PH and “automatically” make it “safe”. Of course the wrong bacteria could take over but then you smell it and you can throw away the milk. What do you think about that?

    Reply
  • July 30, 2022 at 3:04 pm
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    Wonderful article! Would you have the time to write an article addressing raw milk safety testing that could be done on a small herd at home? I periodically test scc and coliform via a lab, but I would love to have a home set up where I could test each batch. If such a thing is feasible.

    Reply
    • August 2, 2022 at 7:42 am
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      Unfortunately, there isn’t really a good way to test for bacteria-of-concern at home. About the only test out there that is simple enough to be done at home is the methylene blue reduction test (what is shown in the header image), and it only informs you of total bacterial load. There is no way to tell whether those bacteria are harmful or harmless. Tests specific to coliforms, or scc tests, require a fair amount of specialized materials and equipment that aren’t really practical in the home environment.

      Reply
      • August 2, 2022 at 9:49 am
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        Thank you for answering my question! I guess my follow up question would be that if the milk passes the methylene test and indicates a very low bacterial load, even if it had one of the dangerous pathogens (e coli, listeria, etc) would it still be enough to cause harm? Is there a minimum amount needed to cause damage? As you can tell, I don’t know much at all on this topic. But we do aim for extremely low scc and coliform counts. I’m not sure if that’s safe enough though?

        Reply
        • August 4, 2022 at 12:29 pm
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          Even with a low methylene blue test, disease from low-abundance pathogens is possible. The main use of methylene blue is to confirm that pasteurization worked, rather than to assess milk risk, although it can be used as a proxy measure for the latter.

          Strictly speaking, 1 viable bacterium is sufficient to cause disease as they can reproduce in the host. While that can happen in theory, in practice you generally need to consume more than 1 bacteria to become ill. Clinically, we measure this using the “minimum infectious dose”, which is the number of bacteria people would need to consume for half of them to develop disease. This value can be pretty variable for different organisms. A few examples:

          • Listeria*, in healthy people: 10-100 million cells
          • Listeria, in pregnant or otherwise susceptible people: 100,000 – 10 million cells
          • Salmonella: 10,000 cells
          • EHEC E. coli: 42 cells

          * I know this sounds like a lot, but keep in mind that Listeria can grow at refrigerator temperatures, and this would be equivalent to the amount of bacteria present in ~2 cups of modestly contaminated milk.

          In your case, you’re already monitoring for pathogens and general signs of infection, so you’re already well ahead of what others are doing to monitor for safety. A methylene blue test may be useful as a way to monitor your herd between more formal testing – e.g. it may identify days where your milking routine is less effective at keeping things clean, or if you take samples from individual animals, may help you identify early onset of disease. I’ll look at putting a post together on the topic.

          Reply
  • July 29, 2022 at 9:17 pm
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    Very well-written and one of your replies to a comment explains why it’s such a good article.

    Thank you.

    But also, it’s ‘lose’, not ‘loose’.

    Reply
  • July 29, 2022 at 12:13 pm
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    All off the above is true. However, the really big picture shows us that food safety creates weak species, and thus a weak human race that will need better and better food “safety” after every generation to come. Right up to the level that they can’t stumach anything annymore. What is good for the individual, is not always good for the species!

    Reply
    • July 29, 2022 at 1:51 pm
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      That’s some nice post-hock rationalization you got there. Be a shame if someone came along and dropped some science on it.

      But before I do, it may be worth pointing out that in real life I run a research lab that investigates human-pathogen interactions. We’ve even published studies on how pathogens have shaped components of the human immune system. Hell, I even teach this stuff to budding new scientists. In other words, we’re now talking about the thing I do for a job…

      Your claim, while common, is completely and utterly false. It is false from the perspective of how our immune systems work, and it is false from the perspective of how evolution works.

      Contrary to what people thing, our immune system does not require continued challenge by pathogens to remain “strong”. And the reason for that is simple – our immune system doesn’t differentiate between pathogens and non-pathogenic organisms, and the entirety of our skin, guts, lungs, and several other organs, are completely filled with bacteria, fungi, viruses, archeans, and parasites, which continually challenge our immune system. Moreover, an absence of pathogens does not lead to weakening of our immune system either – in fact, the opposite is the case. To be pathogenic, a organism must have ways to overcome our immune systems. These mechanisms are often damaging – permanently – to our immune system. Get infected with measles, most of your B cells die and you loose much of your immunological “memory” of past infection. Streptococcal bacteria produce superantigens that will kill or permanently inactive a large portion of your T cells. Heck, even a run-of-the-mill bacterial infection can lead to a general immune suppression that can last for months, through nothing more than the stress it places on your immune system.

      So that’s how your rationalization is wrong from an immunological perspective, now for how its wrong from an evolutionary perspective.

      Central to you claim is the idea that without being continually challenged by gastric pathogens, the lack of selection will lead to loss of the genes required for gastric immune function. This concept is flawed on many different levels. The first is the idea that you must be challenged at a specific tissue for evolution to maintain immunity at that location. This is simply wrong – there is ***an*** immune system, not ***many*** immune systems. Evolutionary pressures from respiratory, skin, or other infections affect the same genes as does evolutionary pressures from gastric infections. After all, it is the same immune cells, sensing the infection by the same immune receptors, and responding in the same immunological manner, which eliminates infections in all sites within our bodies. Moreover, and as I mentioned above, an absence of gastric pathogens does not equate to an absence of gastric immune stimulation – our microbiome continually stimulates the gut immune system, through all the same receptors and pathways as do pathogens.

      But your misunderstanding of evolution is more fundamental than that. The fastest we can evolve at is defined by our mutation rate – the speed of evolution, after all, is measured by the rate of genetic change in a population. Selection is a “break” on evolution – it slows down evolution by reducing the number of genetic variants in a population. Disease is no exception to this – mass outbreaks of disease like the black death lead to the massive “genetic pruning” of the populations gene pool. And this is not a good thing; the loss of genetic diversity in response to one pathogen can open a population up to infection by another pathogen which infects via a different mechanism. As a general rule, the broader the genetic diversity of a population, the better a chance that population has of surviving introduction of a deadly pathogen. Less selective pressure in the form of gastric infections today means that we are not having a lot of kids die before they are 8. It means that the novel genetic mutations they carry (each of us has 100-200 not found in our parents) therefore have a better opportunity to move forwards and enter the broader population. Which means that we, as a population, are developing the genetic tools to resist new pathogens faster now than at any time in our history.

      Reply
  • July 29, 2022 at 9:58 am
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    You write that people largely consumed fermented milk until relatively recently, which makes sense to me. But you focus on Europe. Was this equally true in Africa and India? I seem to remember reading that lactose tolerance evolved independently in northern Europe and Africa. And my impression, from stories like this:

    https://www.newyorker.com/magazine/2018/11/12/cattle-praise-song

    Is that Africans sometimes drink unfermented, unpasteurized milk. I don’t know how far back that tradition goes, though. (And I mean, it’s a fictional story.)

    My other question is, let’s say you’ve got some raw milk of unknown safety (but not noticeably spoiled). Could you bulk pasteurize it yourself and then consume it safely, or would some of the toxins created by pathogenic bacteria be persistent in the milk? Or are there other concerns?

    Reply
    • July 29, 2022 at 10:31 am
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      As I stated in the article, the African “story” of historical milk consumption and the evolution of the lactase tolerance gene is poorly understood, so I cannot answer that question. The African example is also quite different – there are scattered populations of lactase persistent individuals in a region otherwise dominated by lactose intolerant individuals. So unlike the European case, in Africa the spread of the gene was more limited. Unfortunately, research into this area has been minimal, so there isn’t much else we can say about it at this time.

      As for spoiled milk, even after pasteurization it should not be consumed. Bacteria can produce a number of compounds which are unaffected by pasteurization. This may include some toxins (proteins produced by bacteria which are intended to harm the host) as well as toxic metabolites such as biogenic amines. I’ve written an article on the latter: https://suigenerisbrewing.com/index.php/2019/01/22/biogenic-amines/

      Reply

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