Milk: what does it look like? What types exist? Is drinking it as an adult natural? All the secrets of milk–under the microscope!

Milk is a versatile and complete food that has been present in the human diet for millennia and is valuable for the growth and development of mammals of all species. It is widely used in cooking in the production of various foods, which are loved by children and adults from a beautiful slice of the globe. On the other hand, opinions on milk consumption are often debated: consuming milk in adulthood–is it natural?

Today we dive into a cup of milk to discover the richness of its nutrients and shed light on this question once and for all.

Milk under the microscope: what is it made of?

Delicious delicacies such as cream, mascarpone and butter are made from milk. Hundreds of different cheeses can then be produced from it, each with its own particular percentages of components, fragrances, textures and aging.

Curious about how cheese is made? I tried making cheese at home and it was so much fun, I recommend you take a peek! A thousand products and one starting ingredient: milk. But what does milk look like? What’s in it? First, we have to choose: what kind of milk are we talking about?

As we know, it can in fact have various origins, and excellent cheeses are obtained from both cow’s milk and sheep’s and goat’s milk. In this article we discuss the one most consumed today: cow’s milk.

Milk composition

Let’s explore the composition of this fine beverage. Water is the predominant component, making up about 87 percent of the total. It is the nourishment of the pups, who must first and foremost hydrate themselves. Then there is the solid part, which makes up the remaining 13 percent. This is where the real nutrients are concentrated, making milk valuable for growing pups of all mammalian species until they reach weaning age.

The rich nutritional profile of milk includes fats, carbohydrates, proteins, vitamins and minerals. Among them, 3.7% to 5% are fats, while the rest represent non-fat solids. In particular, lactose, the sugar found in milk, accounts for about 5 percent of its total composition. It is important to note that lactose is the only sugar of animal origin: all other sugars come from plant sources. It is a valuable source of energy.

Protein (3.3 percent) is another key element of milk and is divided into casein and serum protein. Caseins, joined together by calcium bonds, are found suspended in milk within structures called micelles. During the cheese-making process, when milk is curdled, caseins are trapped and become part of the cheese, while what remains is the whey rich in seroproteins. This whey is also a source of nutrition and can be used to water livestock. Or, by bringing it to a high temperature again and adding vinegar or lemon juice, the serum proteins coagulate and give rise to the delicious ricotta cheese.


Thus we have seen that milk is composed of fat, protein, carbohydrates, vitamins, minerals and water, a truly complete food in short.

We increase the magnification and enter the magical world of casein micelles and homogenized fat globules, which are found in solution in milk, separated from each other. The structure of milk is complex, and in order for its dissolved components to coexist harmoniously, specialized structures are formed. They are the micelles, which I mentioned just above. In fact, in the watery part of milk there are vitamins, minerals, serum proteins and sugars that are able to dissolve, while caseins and fats cannot and are therefore said to be hydrophobic.

But what is a micelle? We can imagine it as a bubble, the edges of which are composed of particular molecules called phospholipids. They manage to keep the watery part of the milk and the fat components hidden in them from touching. Phospholipids play the role of emulsifiers, surfactants–a bit like soap–making all its components homogeneous even though by nature they would tend to separate like oil in a glass of water.

The taste of milk is the magical result of the fusion of all these components held together to form for all intents and purposes a homogeneous emulsion! It varies from milk to milk depending on the age of the animal, its diet, and the environment in which it lives. Try the alpine milk–and tell me if it is the same as what you buy in the supermarket!

Milk fats and proteins

Turning to milk fats, we discover a variety of fatty acids, such as butyric acid, oleic acid, and palmitic acid. These fats come in different forms, some partially crystallized, and float as majestic heterogeneous fat cells within the semi-solid magma of milk.

Next to this set of fats we find caseins, a family composed of several different proteins. Two of them, alpha and beta caseins, cannot touch water. The k-caseins, their less shy sisters, have portions in their structure that they can use as a screen and so … put themselves around the alpha and beta caseins, thus forming a protective bubble. Internally, calcium bonds form between the caseins, making this aggregation more solid. When an acid or curing agent is added, the calcium bonds are broken and the proteins precipitate.

Milk is a universe of wonders hidden from our sight, where the finer details are revealed only throughmicroscopic analysis. This complex ballet of elements is what makes milk such a unique and fascinating food, inspiring constant research and studies to unravel all its hidden secrets.

The different types of milk: raw, UHT, whole, skimmed and semi-skimmed

At the supermarket, in the appropriate department, we are faced with awide variety of milks to choose from. Each has its own specific characteristics: we have skim, part-skim and whole milk indicating a difference in fat content; we then have different options that are characterized by heat treatment such as UHT, microfiltered, pasteurized and raw milk.

Let’s take a closer look at them.

Raw milk is that which has not undergone pasteurization, a heat treatment used to eliminate pathogenic bacteria. As a result, raw milk may contain both beneficial and potentially harmful bacteria. The likelihood of incurring a pathogen is generally low because if stored properly in a refrigerator, low temperatures stop the proliferation of bacteria. This means that, if there were, their impact on the immune system of healthy people would be manageable and limited in most cases. However, in 2010 there were some serious cases of infection that led the Ministry to introduce a requirement to put the words “to be consumed after boiling” on bottles of raw milk. With boiling, the risk becomes practically zero.

In the pasteurization process, milk is heated to specific temperatures, usually between 70 and 75°C for a period of time of 10 to 15 seconds. This is enough to kill pathogenic bacteria but without eliminating many other microorganisms present. Pasteurized milk, which is what we commonly find in supermarket refrigerators, has a longer shelf life than raw milk. However, since it contains a certain amount of microorganisms, if left out of the refrigerator for a prolonged period it tends to curdle and deteriorate as the lactic acid bacteria present begin to ferment the lactose, lowering the pH and causing the milk to coagulate.

UHT (Ultra High Temperature) milk undergoes an even more intense heat treatment, exceeding 130 degrees for a few seconds and thus eliminating all microorganisms present. This process, while ensuring storage at room temperature, may result in a slight alteration of the milk’s proteins and sugars slightly affecting its flavor, which may seem more “cooked.” However, do not think that this milk is somehow low in nutrients: the high temperatures still allow its nutritional values to be preserved.

In addition to these different treatment variations, we can divide milk into three main categories, mainly based on fat content:

  1. Whole milk: contains at least 3.5 percent fat.
  2. Partly skimmed milk: contains 1.5% to 1.8% fat.
  3. Skim milk: has a fat content of less than 0.5 percent.

Choosing the type of milk best suited to one’s needs and preferences is a personal decision, but regardless of the choice, milk remains an excellent source of nutrients.

What is milk pellicle?

The skin of milk is nothing but the fruit of the coagulation of serum proteins! As temperatures rise due to cooking, they lose their structure and become–a thin, concentrated sheet of protein, basically. Nothing to scoff at seen like that, right?

Is drinking milk as an adult natural?

Milk has been the focus of discordant discussions and opinions for decades, fueled by “scientific” articles sourced from self-styled experts who boast of holding secret truths. It is time for clarity!

This issue has been discussed for many years, but why does it happen?

Earlier we said that milk is a complete food, and that its primary purpose is to feed puppies. What raises doubts and criticism of milk consumption is at the very bottom of the last sentence: puppies. In fact, in all animal species that feed on milk, once weaning has taken place we feed on something else. Humans are the only mammals that continue to feed on milk even after weaning. And not human milk, but belonging to another: bovine milk.

It is then not difficult to understand why fears and doubts are triggered in the collective imagination.

“Will it hurt? We are adults and this product is cow after all. It’s unnatural!”
“I don’t know, I read around that we can’t digest it, that it’s poisonous.”

Let’s have clarity.

First of all, how do we digest milk as children?

Thanks to an enzyme that, look fancy, is called lactase , and yes, it digests lactose. It breaks it down into its basic components, glucose and galactose, which are absorbed by our bodies and used as energy. This enzyme is encoded by a gene that around age 5 is “turned off.” As a result, lactase is no longer produced and the lactose reaches the gut, where the microbiota feeds on it, producing gas and causing all the unpleasant consequences that afflict the intolerant.

But is this really the case?

A large proportion of the world’s population is, in fact, lactose intolerant.

But what about those who can digest it instead?

One third of the world’s population has what is known as “lactase persistence“: in these individuals, the gene that produces the lactase enzyme does not turn off after weaning and continues to allow lactose digestion.

One-third of the world’s population, not chump change! We cannot ignore this fundamental fact, which, in fact, has been and is still being researched today. Let’s see what we found out about this.

During specific studies on this gene, scholars noticed something very interesting: the world population that continues to express this gene is not evenly distributed around the world.

The eastern regions of the world, such as Asia and Oceania, have a very high percentage of lactose intolerant people, while Europe and North Africa are rich in individuals who can digest it. In general, we can say that in the Global North it is easier to find milk-digesting populations while it is gradually less likely as we move to the Global South.

Why this distribution?

Genetic mutations present in the milk-digesting part of the population were discovered in the 2000s. These mutations lead to the gene responsible for lactase not being turned off, allowing those with these mutations to continue drinking milk without digestive problems. What is interesting is that several mutations have been discovered, occurring in different places around the world, but leading to the same end effect: being able to digest milk even in adulthood.

This suggests something very important, making us think about what we can consider “natural” or not. Environmental events affect selection, which brings random mutations. Individuals that are better adapted as they mutate are more likely to survive and reproduce. In areas where these mutations have been passed down, what conditions do we find? A culture and tradition made up of cattle breeders, who sometimes had less availability of other types of food. The Nordic countries, for example, could not rely on large varieties and quantities of fruits, vegetables, and grains especially during winter periods. The ability to have livestock and feed on milk was probably crucial for them.

In general, this mutation is found precisely in those populations that have a tradition in animal husbandry and pastoralism. It is precisely here that this mutation is selected as a winner: because it makes a difference.

Another consideration: several studies have led to the understanding that before livestock farming, human beings were unable to digest milk. After all, what would we do with that mutation? It is possible that it occurred by chance, but that it was not then selected and passed on because it did not constitute many advantages.

Then, however, we started breeding. At first, livestock were used to produce meat and dairy products such as butter and cheese, which had little lactose. The mutation of the lactase persistence appeared randomly – mantra: mutations ALWAYS happen randomly – in individuals who then used milk, and … magic. Everything worked. No intestinal problems! As a result, these individuals lived longer and reproduced more successfully, suffered fewer malnutrition problems et voila. Within a short time, in these breeder populations the mutation became predominant.

What can we infer from this chain of events?

That adaptation to digest milk even as adults was part of our natural evolution. It turned out to be convenient to know how to do it, and it is a perfect example of Darwin’s natural selection. That, so unnatural well… it’s not 😉

We came to the conclusion of this article, in which we analyzed milk under the microscope by looking at its components, the different types and on what basis they are classified. We then addressed the age-old question of the “naturalness” of its consumption and discovered that evolution follows sometimes surprising paths. And for those who are not fortunate enough to possess the lactase persistence mutation well…there is still lactose-free milk.

Good glass of milk to everyone!

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