Milk is life.
Milk is an extremely rich resource. It is available in a wide range of forms, processed to varying degrees, in settings as different as direct farm sales and city supermarkets. Of all foods, milk comes closest to being the ideal “complete” solution.
“Milk is the integral product of the complete, uninterrupted milking of a healthy, well-fed female animal which is not overworked. It must be collected in clean conditions and shall not contain colostrum.” (Official definition, 1909)
The mother’s milk is the first food mammals consume. It is the source of life. It contains vital substances which give the young animal an excellent start on the path to growth, especially just after birth.
Milk is a sweetish white liquid secreted by the mammary glands of some 4,000 mammal species. It is essential not just for babies but throughout human life, in childhood, adolescence, adulthood and old age.
85% of the world’s milk is produced by cows
In 2004, cow’s milk accounted for 520m of the 628m tonnes of milk produced in the world. Other species are almost insignificant in comparison: 88m tonnes of buffalo’s milk, 12.7m tonnes of goat’s milk and 7.8m tonnes of sheep’s milk.
Mare’s milk provides the raw material for kefir and kumis, slightly fizzy fermented alcoholic drinks traditionally consumed in Caucasia and central Asia.
Milk is a key part of life, both a source of food and a symbol of purity, synonymous with wealth and abundance. It has existed down through the ages and even today remains key to our daily diets, featuring high on the list of the most frequently consumed foods.
As an essential food, milk forms a bond between the mother and her young. As a universal living substance, it has been the raw material underpinning domestic economies since time immemorial. Very early on, it was transformed into a wide range of products so that it could be stored.
A 100% natural product
In 2002, the average French person consumed 73.3 litres of liquid milk.
Not confined solely to the breakfast table, it is a key cooking ingredient: 86% of French people use milk to prepare desserts, vegetable mashes, baked vegetable dishes and soups.
Although various heating processes help us store milk for longer, it remains a natural product and contains no preservatives.
It is easy to store and is sold in practical, hygienic packs.
Milk and dairy products are the richest sources of calcium in our diets. Milk contains 120mg per 100ml. Most other foods, even those we think of as good sources of calcium, contain much less. For example, an average of 35mg per 100g for fresh vegetables and 20 to 40mg per 100g for citrus fruit.
Milk, a raw material
A complex raw material
Milk is constituted of a large number of different substances. Chemical analysis reveals a wide variety of ions and molecules. This is not, however, a random collection of substances – the mix is structured. Changing the temperature and acidity of milk even very slightly alters the initial balance, opening up a wide range of processing possibilities.
Voyage to the centre of a drop of milk
The water molecules move constantly: salts, proteins and fats are suspended in the water part of the milk as particles of varying sizes, from tiny metallic ions to globules of fat. Caught up in this constant melee of water, ions and molecules of various types, soluble protein aggregates and casein micelles move randomly, travelling first in one direction then suddenly veering off in another.
Water, which makes up 80% of our bodyweight, is also the principal constituent of milk, with 905g in each litre. Via our blood, water carries oxygen and nutrients to all parts of our bodies. It also eliminates toxins through the kidneys and enables the body to regulate its temperature.
Water molecules roll and slide over one another at a speed of several hundred metres per second, crashing into and hooking an immeasurable number of different molecules and ions, sweeping them all along in a zigzagging path.
They push hither and thither casein molecules, which never meet because they repel one another, but are 30 to 300 times bigger than the lactose molecules. In this turbulent stream, fat globules 100, 1,000 or 10,000 times larger than the casein micelles occasionally appear.
Far too large to be buffeted by the water molecules, they slowly rise towards the surface of the milk where they stick together to form great clusters of fat.
Milk proteins are chains of amino acids with a variety of compositions and structures. Milk contains caseins, held in suspension in the water, and soluble whey proteins.
Caseins are the main milk proteins, but they are not a homogeneous group. There are several different types, categorised by their amino acid profiles.
They tend to group together in aggregates of hundreds or millions of molecules. The white colour of milk comes from its casein micelles, macromolecules rich in mineral salts – especially calcium – which are negatively charged and therefore repel one another.
If the environment becomes more acidic, casein micelles are destabilised and bond together to form a casein network. This is when milk coagulates.
Whey proteins can withstand a slightly more acid environment. They also differ from caseins in terms of their composition and their sensitivity to heat, which denatures them and disrupts their structures. Some whey proteins (immunoglobulins) are antibodies, antibacterial substances present in milk.
Whey is the carbohydrate found in milk. It is also known as “milk sugar”. Each litre of milk contains 49g of sugar, the equivalent of 12 sugar lumps (the sweetening power of lactose is low – 6 times lower than that of sucrose from sugar beets). In the intestine, lactose encourages the growth of bacteria which inhibit harmful microbes. It also aids the absorption of calcium.
Milk fat is an extraordinarily complex blend of diverse molecules. It is constituted mainly of triglycerides, derived from three fatty acids and glycerol, an alcohol.
There are more than 150 different fatty acids in milk.
As the fat is insoluble in water, it creates an emulsion composed of a multitude of spherical drops, each formed of a cluster of fat surrounded by a membrane.
As these drops are less dense than water, they rise gently, bunching together as they do so. This natural but reversible separation forms cream, a blend of skimmed milk and pure fat.
Milk contains around 9g of minerals per litre (1.3g of calcium, 1g of phosphorus, 1.6g of potassium, 1.1g of chloride, 0.5g of sodium and 0.14g of magnesium).
It is the perfect source of calcium for bones and teeth because it also contains, in the required proportions, the phosphorus and vitamin D the body needs to absorb the calcium.
Milk contains two categories of vitamins:
- Water soluble vitamins, soluble in water and whey (vitamins B and C)
- Fat soluble vitamins, soluble in fat and therefore cream (vitamins A, D and E; skimmed milk does not contain fat soluble vitamins). Milk contains almost all the vitamins the body needs to live, with the exception of vitamin C which can be obtained from fruit and vegetables. Additionally, milk does not contain iron. This can be rectified easily by adding a little cocoa powder, for example.
Milk, a complete food
Milk, a complex food
Milk is almost 90% water. It is a very rich liquid containing most of the nutrients our bodies require throughout life: the water hydrates our bodies, protein and mineral salts (calcium, phosphorus, etc.) build them, carbohydrates and fatsgive us energy and vitamins protect us.
An energy-giving food
A litre of whole milk provides over 650 calories. Milk sugar (lactose) gives us instant energy; the fats, made up of 64% saturated fatty acids and 36% unsaturated fatty acids (mainly monounsaturated), provide energy and also play an important structural role in our bodies: they are major constituents of our cell membranes, particularly in the nervous system.
Proteins with excellent nutritional value
Milk proteins contain all the indispensable amino acids (those which the body cannot synthesise and must obtain from food).
The proteins in milk have a higher nutritional value than vegetable proteins, which lack one or more of the essential amino acids.
An irreplaceable source of calcium
Milk contains 120mg of calcium per 100g, far exceeding the calcium content of other foods (e.g. meat 10mg per 100g, fish 27mg per 100g, vegetables 35mg per 100g). A mug of milk provides more than a third of an adult’s recommended daily amount of calcium. Moreover, the other elements present alongside it, in particular protein and lactose, ensure the calcium found is milk is absorbed efficiently by the body.
Milk also contains other mineral salts such as phosphorus, magnesium, sodium and numerous trace elements.
Milk contains many vitamins. Some are dissolved in the fat, others are dissolved in the water. Milk is particularly rich in vitamin A, required for vision, to protect skin and to fight infection. It is also rich in Bgroup vitamins, especially B2 and B12. It also contains smaller quantities or traces of other vitamins (C, D, E, K and PP).
Milk, a fundamental raw material
Milk, the fundamental raw material behind numerous dairy products
When milk is processed, it passes its nutritional properties on to other dairy products. However, cheese, yoghurt, fermented milk, butter and cream all have their own specific qualities.
Cheese is the calciumchampion. Cooked pressed cheeses (Emmental, Comté, Beaufort, etc.) contain a record level – over 1g of calcium per 100g of cheese.
Cheese is also rich in B group vitamins. Blue cheeses and the Camembert family contain particularly high levels of B group vitamins, produced during the fermentation process.
Fromage frais is an excellent source of protein, with 7 to 8.5g per 100g. It is also rich in calcium, with 70 to 140mg per 100g. Carbohydrate content ranges from 3 to 18%, depending on the quantity of lactose and sucrose present when sugar or fruit is added. Fructose also adds to the carbohydrate content if the fromage frais contains fruit pieces, coulis or pulp.
- Soft cheeses such as Camembert. The cheese is moulded after coagulating and left to drain naturally.
- Fresh cheeses such as Mozzarella. The curds are heated and worked mechanically to obtain a specific texture. These are called pasta filata (spun paste) cheeses.
- Pressed cheeses such as Emmental or St Paulin.The curds are pressed to encourage the whey to drain out. For Emmental, they are heated first. These cheeses are generally large; a single Emmental weighs in at 80 to 100kg. More pressed cheeses are produced in the world than any other type. They account for 40% of global production.
- Veined cheeses such as RoquefortThe penicillium roqueforti cultures cause mould to grow inside the cheese, giving it its characteristic blue- or black-veined appearance.
Yoghurt and fermented milk
Yoghurt and fermented milk contain lactic cultures which predigest the milk. As a result, these products are extremely easy to digest and beneficial for intestinal flora.
Classification of yoghurt and fermented milk
- Set yoghurts
- Churned yoghurts
- Drinking yoghurts
Butter has existed for over 3,000 years, but for much of that time it remained a rare food, produced artisanally on a local scale.
In 1859, CJ Fuchs discovered that fat could be separated from milk by centrifugation. In 1864, the cream separator was invented. This machine was a key factor in the rapid growth of butter manufacturing. It helped the dairy industry develop by making large-scale production a reality.
Butter is made from cream, which is produced by skimming milk.
Ten litres of milk yield one litre of cream. The cream is pumped into maturing tanks and cultured with lactic leaven.
Butter crystals form during the maturing process. The saturated cream is then shaken vigorously, a process known as churning.
The fat globules stick together to form butter grains. The liquid given off during the process is called buttermilk.
Butter is a concentrate of fat from milk. As the vitamins A and D in milk are held in the fat, butter is the second-richest dietary source of vitamin A, second only to liver. A 25g portion of butter supplies 25% of an adult’s daily recommended amount of vitamin A. Vitamin A is essential for many of the body’s processes, including growth, visual mechanisms, the vitality of skin, resistance to infection and more.
Classification of butter
- Classic pasteurised butter, 82% fat
- Raw butter, from raw cream
- Spreadable butter (soft butter)
- Lighter options
- Reduced-fat butter (60 to 62%)
- Low-fat butter (39 to 41%)
Cream is also a source of vitamins A and D. With 15 to 30% fat, it is the least rich in fat of the products we know as “fats”.