Cow's milk is roughly 87% water; the rest is mainly fat (about 3.3–5.4%), protein (about 3.0–3.9%, nearly 80% of it casein), lactose (about 4.4–5.6%) and minerals (about 0.7–0.8%), with the exact mix depending on breed, diet and stage of lactation. Dairy products are made by separating, heating, fermenting, coagulating, concentrating or drying these components. UK official statistics, for example, use about 9.5 litres of milk per kg of cheddar and 8.5 litres per kg of whole milk powder.
Reviewed by John Watson FIFST, dairy technologist and founder of Watson Dairy Consulting.
What milk is
Milk is the fluid that female mammals produce to feed their young. Most of the milk people drink and process comes from cows, with water buffalo the second biggest source worldwide; goats, sheep and camels matter in particular regions. Milk is mostly water carrying fat globules, proteins, the milk sugar lactose and minerals. Everything except the water is called total solids, and the solids other than fat are known as solids-not-fat (SNF).
Typical composition of cow's milk
Cow's milk is roughly seven-eighths water. The solids are what processors turn into products, so their make-up decides how much cheese, butter or powder each litre yields. Individual herds and seasons can fall outside these typical ranges.
| Component | Typical range | Notes |
|---|---|---|
| Water | about 86–88% | Calculated as 100% minus total solids; US farm milk averaged 86.6% water in 2025 |
| Fat | 3.3–5.4% | The most variable component; US farm milk averaged 4.3% fat in 2025 |
| Protein | 3.0–3.9% | Nearly 80% casein, the rest whey proteins |
| Lactose | 4.4–5.6% | The milk sugar and main carbohydrate |
| Minerals (ash) | 0.7–0.8% | Includes about 112 mg of calcium per 100 g on average |
| Total solids | about 12–14% | Breed averages run from about 12.2% (Holstein) to 14.0% (Jersey) |
Sources: Roy et al., Frontiers in Nutrition, 2020 (fat, protein, lactose, ash); USDA Economic Research Service, Dairy Data documentation, 2025 data (US averages); New Mexico State University Guide D-103, 2001 (breed averages); FAO, Milk and dairy products in human nutrition, 2013 (casein share, calcium)
Casein and whey proteins
Milk protein falls into two groups. Casein makes up nearly 80% of the protein in cow's milk and is the fraction that clots to form curd in cheese making. The whey proteins, around 20%, stay dissolved in the liquid whey that drains from the curd. In one set of reference values for normal milk, casein was 2.8% and whey protein 0.8% of the milk.
Why composition varies
No two herds give exactly the same milk. The main influences are:
- Breed: Jersey milk averages about 4.6% fat and 3.7% protein, compared with about 3.6% fat and 3.2% protein for Holstein milk
- Diet: fat is the most responsive component and can shift by nearly 3 percentage points with feeding, while protein moves by about 0.6 points
- Stage of lactation: fat and protein are highest early and late in lactation and lowest from peak yield through mid-lactation
- Season and udder health: fat and protein tend to be higher in autumn and winter, and mastitis (shown by a high somatic cell count) lowers casein and lactose
Milk from cows, buffalo, goats, sheep and camels
Milk from other dairy species differs markedly from cow's milk. Buffalo milk has, on average, about twice the fat of cow's milk and a high proportion of casein that suits cheese making, while sheep milk is richer than both cow and goat milk in fat and protein. Goat and camel milk are closer to cow's milk in overall make-up, although camel milk is slightly saltier.
| Species | Fat | Protein | Lactose | Total solids |
|---|---|---|---|---|
| Cow | 3.3–5.4 | 3.0–3.9 | 4.4–5.6 | 11.8–13.0 |
| Buffalo | 5.3–9.0 | 2.7–4.7 | 3.2–4.9 | 15.7–17.2 |
| Goat | 3.0–7.2 | 3.0–5.2 | 3.2–5.0 | 11.9–16.3 |
| Sheep | 5.0–9.0 | 4.5–7.0 | 4.1–5.9 | 18.1–20.0 |
| Camel | 2.0–6.0 | 2.4–4.2 | 3.5–5.1 | 11.9–15.0 |
Source: Roy, Ye, Moughan and Singh, 'Composition, Structure, and Digestive Dynamics of Milk From Different Species – A Review', Frontiers in Nutrition, 2020 (Table 1)
The ranges are wide because they pool studies of different breeds, diets and stages of lactation. FAO's 2013 averages sit inside them: about 7.5% fat for buffalo, 6.4% for sheep, 3.9% for goat and 3.2% for dromedary camel milk. Goat, sheep and camel milk also have a slightly lower casein share than cow's milk, and many modern dairy herds produce richer milk than the cow range shown here.
How the main dairy products are made
Liquid milk: pasteurised, ESL and UHT
Milk is cooled on the farm and kept cold until it is processed; FAO describes cold storage of raw milk as probably the biggest single factor in raw milk quality. At the dairy, milk is usually standardised, meaning its fat content is adjusted to a set level by removing cream or blending in skimmed milk, and then heat treated.
Pasteurisation must be at least as effective as heating every particle of milk to 72 °C for 15 seconds (continuous flow) or 63 °C for 30 minutes (batch), conditions designed to destroy the organisms that cause tuberculosis and Q fever; the milk must then be kept chilled. UHT (ultra-high temperature) milk is heated, typically to 135–150 °C for 2–10 seconds, and packed aseptically, so it keeps unopened at room temperature. Extended shelf life (ESL) milk is still sold chilled, but an extra step, such as microfiltration or a higher-temperature treatment, lets it keep longer than standard pasteurised milk. In the United States, for example, 'ultra-pasteurised' milk is heated to at least 138 °C (280 °F) for at least 2 seconds.
Homogenisation is a separate mechanical step that breaks the fat globules into much smaller ones so that cream no longer rises to the top. One legal test is that no visible cream layer should form after 48 hours of cold storage.
Cream and butter
Cream is the fat-rich part of milk, separated by skimming or centrifuging. Churning cream produces butter, an emulsion of milk fat and water that is about 81% fat and 16% water, and leaves buttermilk behind. Heating butter to remove its water gives ghee, which keeps for 6–8 months or longer; anhydrous milk fat and butter oil are related products. Because separation yields both cream and skimmed milk, butter and skimmed milk powder are often made side by side.
Cheese
Cheese making concentrates the casein and most of the fat of milk. In one University of Guelph example, about 93% of the milk fat and 78% of the protein ended up in the cheese, but only about 4% of the lactose. The milk is coagulated, usually with rennet enzymes, though some cheeses are set with acid, or with acid and heat of about 90 °C. The curd is cut, cooked, stirred, drained, moulded, pressed and salted to expel whey, and most rennet-set cheeses are then ripened. There are an estimated 1,400 varieties.
Yogurt and fermented milks
Fermented milks are made by adding live cultures that turn part of the lactose into lactic acid, which sours and thickens the milk. For yogurt, the milk, often enriched with extra milk solids, is homogenised and heated (typically 85 °C for 30 minutes or 95 °C for 5 minutes), cooled to about 42 °C, inoculated and held for about four and a half hours until the pH falls towards 4.6 and the proteins set. Codex defines yogurt by its two characteristic bacteria, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Kefir, made with grains of yeasts and bacteria, and Indian dahi are other examples.
Milk powders: SMP and WMP
Milk powders are made by removing almost all of the water, usually by evaporating milk to a concentrate and then spray drying it. Under the Codex standard, skimmed milk powder (SMP) contains no more than 1.5% fat, whole milk powder (WMP) contains 26–42% fat, and both may contain no more than 5% water. Stored cool and dry, SMP keeps for about three years; WMP has a shorter shelf life because its fat turns rancid more easily. Adding water back to powder gives reconstituted milk.
Whey and whey products
Whey is the liquid left after the curd forms. Sweet whey comes from rennet-set cheeses; acid whey comes from acid-set types such as cottage cheese and holds about twice as much calcium. Whey carries the whey proteins, most of the lactose and water-soluble vitamins. It is dried into whey powder (Codex sweet whey powder has at least 10% milk protein and around 61% lactose), separated into whey protein concentrates and isolates, used to make lactose, or heated to make whey cheeses.
Condensed and evaporated milk
Both are milk with part of its water removed. Evaporated milk is unsweetened and sterilised in its sealed can (around 120 °C for 13 minutes is one quoted condition), with a Codex minimum of 7.5% milk fat. Sweetened condensed milk has added sugar, typically about 43–45% of the finished product (roughly 60% of its solids); this high sugar level, not sterilisation, stops microbes growing. Its Codex minimum is 8% milk fat.
Ice cream
Ice cream is made by freezing a pasteurised mix of dairy ingredients, such as milk, cream and milk solids, and sweeteners while stirring, which also works in air. Legal definitions vary. In the United States, ice cream needs at least 10% milk fat, normally at least 10% non-fat milk solids, and a weight of at least 4.5 lb per US gallon (about 540 g per litre), which limits the amount of air.
Infant formula
Infant formula is a breast-milk substitute made to meet, on its own, the nutritional needs of babies in their first months. It can be based on cow's milk, other animals' milk or other proven ingredients such as soy protein. The international Codex standard sets minimum and maximum levels for energy, protein, fat, vitamins and minerals, requires ingredients to be gluten-free, and is applied alongside the International Code of Marketing of Breast-milk Substitutes. This page is general information, not nutrition or medical advice: for questions about feeding a baby, follow the advice of a doctor, midwife or other health professional.
Typical milk-to-product yields
Yields depend on the fat and protein content of the milk and on how much moisture the finished product keeps, so the figures below are averages rather than fixed rules.
| Product | Made from | Amount per kg of product | Source |
|---|---|---|---|
| Cheddar cheese | Whole milk | about 9.1–9.5 litres | Defra 2026; Teagasc |
| Mozzarella, blue-veined and long-life UK territorial cheeses | Milk | about 9.1–9.8 litres | Defra 2026 |
| Soft cheese | Milk | about 8 litres | Defra 2026 |
| Butter | Whole milk | about 21–22 kg | FAO 2013; UW–Madison Extension 2025 |
| Butter | Cream | about 2 litres (2.04) | Defra 2026 |
| Skimmed milk powder (SMP) | Skimmed milk | about 10 litres (10.1) | Defra 2026; FAO 2013 |
| Whole milk powder (WMP) | Whole milk | about 8.5 litres | Defra 2026 |
| Condensed milk | Milk | about 2.7 litres | Defra 2026 |
| Yogurt | Milk | about 1.1 litres | Defra 2026 |
Sources: Defra, Milk utilisation statistics notice (Table 4.1, conversion factors), 2026; Teagasc, Production of farmhouse cheese, 2025; FAO, Milk and dairy products in human nutrition, 2013; University of Wisconsin–Madison Division of Extension, 2025
Defra's factors are UK averages advised by the dairy industry and vary from month to month. The lower cheddar figure comes from a Teagasc example in which a 500-litre vat yields about 55 kg of hard cheese. The butter range reflects FAO's world average of 4.7 kg of butter per 100 kg of whole milk and a University of Wisconsin–Madison figure of 21.8 lb of milk per lb of butter. The SMP figure is in litres of skimmed milk, not whole milk.
A short history of dairying
Dairying began with the domestication of livestock about 10,000 years ago. Analysis of more than 2,200 pottery vessels shows that people in the Near East and south-eastern Europe were using milk by the seventh millennium BC, especially in north-western Anatolia. The first cheese may have been made by accident, as milk stored in bags made from animal stomachs would curdle. Some of the earliest direct evidence of cheese making comes from pottery sieves with milk-fat residues from the sixth millennium BC in temperate Europe.
Preserving milk fat is also ancient: ghee has been made in India since about 1500 BC. Safe liquid milk came much later. Louis Pasteur patented a heating process to stop wine spoiling in 1865, and the same principle was later applied to milk to destroy disease-causing organisms such as those that cause tuberculosis. Cities then wrote it into law; in Chicago, for example, pasteurisation first entered the city's rules in 1908 and was fully compulsory by 1916.
FAO identifies cold storage of raw milk as probably the biggest single influence on raw milk quality, and lists pasteurisation, UHT treatment and sterile packaging as the other key advances in processing, with membrane filtration, enzyme technology and new packaging among other significant developments. FAO also notes that dairy plants around the world are developing along very similar lines.
Careers in dairy processing
Turning milk into safe, consistent products takes skilled people at every stage. Dairy process operators run separators, pasteurisers, evaporators and dryers; cheesemakers, buttermakers, yogurt makers and ice cream makers manage the product-specific steps; and dairy technologists look after quality, product development and process control. Browse our dairy job descriptions or start with our overview of dairy careers.
Work in dairy? Browse live dairy jobs, explore dairy careers or create a free job alert. Employers can advertise a dairy vacancy.
Frequently asked questions
Cow's milk is roughly 87% water. The rest is mainly fat (about 3.3–5.4%), protein (about 3.0–3.9%), lactose (about 4.4–5.6%) and minerals (about 0.7–0.8%), with the exact mix depending on breed, diet and stage of lactation.
For cheddar, UK official statistics use about 9.5 litres of milk per kg, and most other hard and semi-hard cheeses need roughly 9–10 litres. Soft and fresh cheeses need less because they keep more water.
Casein is nearly 80% of the protein in cow's milk and is the part that clots to form cheese curd. Whey proteins make up the remaining 20% or so and stay in the liquid whey, which is made into whey powders and protein concentrates.
Pasteurised milk is heated to at least the equivalent of 72 °C for 15 seconds and must be kept chilled. UHT milk is heated to 135–150 °C for a few seconds and packed aseptically, so it keeps unopened at room temperature. ESL milk is still chilled but has an extra treatment, such as microfiltration or higher heat, so it lasts longer than standard pasteurised milk.
Of these five, buffalo and sheep milk are the richest, typically about 5–9% fat, compared with about 3.3–5.4% for cow's milk. Buffalo milk's high fat and casein content makes it especially well suited to cheese making.
Sources
- FAO – Milk and dairy products in human nutrition (Chapter 2, dairy processing developments; Chapter 3, Milk and dairy product composition; Tables 3.1, 3.2, 3.3, 3.7; dairy commodity tree) (2013)
- FAO – Dairy production and products gateway: Milk composition (undated (accessed 2026))
- Roy D, Ye A, Moughan PJ, Singh H – Composition, Structure, and Digestive Dynamics of Milk From Different Species: A Review, Frontiers in Nutrition 7:577759 (2020)
- USDA Economic Research Service – Dairy Data: documentation (US farm milk composition) (2025 data (page updated 2026))
- New Mexico State University – Managing Milk Composition: Normal Sources of Variation (Guide D-103) (2001)
- Defra – Milk utilisation statistics notice (data to September 2026), Table 4.1 conversion factors (2026)
- Teagasc – Production of farmhouse cheese (2025)
- University of Wisconsin–Madison Division of Extension – Milk, Cookies, and Christmas Eve: Santa's Dairy Tab by the Numbers (2025)
- AHDB – Market indicators: AMPE, MCVE and Milk Market Value (butter and SMP made from the same milk) (2026)
- University of Guelph, Department of Food Science – Table 12.1: Distribution of milk components during cheese making (undated (accessed 2026))
- Codex Alimentarius – Standard for Infant Formula and Formulas for Special Medical Purposes Intended for Infants (CXS 72-1981) (1981 (version amended 2015))
- US Electronic Code of Federal Regulations (eCFR), 21 CFR 131.3 – Definitions (pasteurized, ultra-pasteurized) (current (accessed 2026))
- US Electronic Code of Federal Regulations (eCFR), 21 CFR 135.110 – Ice cream and frozen custard (current (accessed 2026))
- California Legislative Information: Food and Agricultural Code, Section 35941 (current (accessed 2026))
- Tetra Pak Dairy Processing Handbook – Chapter 17, Condensed milk (Table 17.1, typical composition of sweetened condensed milk) (undated (accessed 2026))
- Hoffmann W et al. – Processing of extended shelf life milk using microfiltration, International Journal of Dairy Technology 59(4):229–235 (2006)
- Evershed RP et al. – Earliest date for milk use in the Near East and southeastern Europe linked to cattle herding, Nature 455:528–531 (2008)
- Salque M et al. – Earliest evidence for cheese making in the sixth millennium BC in northern Europe, Nature 493:522–525 (2013)
- Institut Pasteur – Louis Pasteur: a universal legacy (2022 (updated 2024))
- Czaplicki A – 'Pure Milk Is Better Than Purified Milk': Pasteurization and Milk Purity in Chicago, 1908–1916, Social Science History 31(3):411–433 (2007)
This page is general information about milk and dairy products. It is not nutrition or medical advice.
Last reviewed: November 2026. © 2026 Dairy Jobs (Specialist Recruiters Ltd).