Introduction

Dairy products are those obtained from milk through appropriate technological treatments. Today we’ll explore yoghurt, curd, cottage cheese, cream and cheese.

Yoghurt and Similar Products

Yoghurt is a gelled and acidic dairy product, with added ingredients that give it its characteristic flavour and colour. It is produced by the fermentation of lactose. During fermentation, bacterial enzymes hydrolyse lactose, transforming galactose into glucose. Glycolysis then leads to the formation of lactic acid.

As lactic acid is produced, the pH drops to 4.6. This eliminates pathogenic flora and allows acidophilic and thermophilic flora to proliferate. Casein partially coagulates, forming a gel made of a network of bound micelles, which gives yoghurt its typical consistency.

Yoghurt Composition

• 85% water
• 4% protein
• 3% fat
• 3.5% lactose
• 0.9% mineral salts
• 1% lactic acid

Yoghurt production involves:

• Pasteurisation and homogenisation
• Inoculation with microbial culture
• Incubation at 40–45 ºC
• Packaging

The most common fermentation bacteria are Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, among others like L. bifidus.

For bio yoghurts, Lactobacillus acidophilus is used, resulting in a less aromatic but creamier product.

The characteristic flavour of yoghurt comes from aromatic compounds formed during fermentation, such as diacetyl, acetaldehyde and acetoin.

Pasteurised yoghurts have longer shelf lives but often lack live bacteria—one of yoghurt’s main benefits.

Compared to milk, yoghurt offers:

• Easier to digest proteins
• The acidity inhibits harmful intestinal flora

However, yoghurt doesn’t replenish gut bacteria as its microorganisms are sensitive to stomach acid, unlike Lactobacillus bifidus and acidophilus.

Studies show yoghurt may benefit the immune system.

Natural yoghurt provides 62 kcal, 3g fat, 3.4g protein, 13mg cholesterol, and 121mg calcium per 100g.

Curd

Curd is produced by heating milk and adding rennet, resulting in a firm, protein-rich mass due to its high casein content. It’s rich in calcium and has less fat and cholesterol than the original milk.

Per 100g: 90 kcal, 5.2g protein, 4.6g fat, 11mg cholesterol, 224mg calcium.

Cottage Cheese

Made by precipitating the proteins in whey using heat and acid after milk coagulation for cheese-making. It forms a white, soft, crustless mass.

It’s rich in protein and contains ~5% fat.

Per 100g: 101 kcal, 12.5g protein, 4.5g fat, 15mg cholesterol, 60mg calcium.

Cream

According to the Spanish Food Code:

“Cream is the fat-rich product separated from milk by resting or centrifugation. It is made from cow’s milk from healthy animals.”

Cream is an oil-in-water emulsion and exists in several types:

• Double cream: ≥50% fat (centrifuged)
• Cream: 30–50% fat
• Light cream: 12–30% fat

Based on hygiene and conservation treatment:

• Pasteurised cream
• Sterilised cream
• UHT cream
• Pressurised pasteurised cream
• Pressurised UHT cream
• Frozen cream
• Powdered cream

Typical kitchen cream has just over 30% fat. Per 100g: 317 kcal, 2.2g protein, 32.9g fat, 85.5mg cholesterol, 85mg calcium.

Cheese

Cheese is a fresh or aged product obtained by separating whey after coagulating natural, semi-skimmed or skimmed milk, cream or mixtures thereof, using rennet or other coagulants, sometimes preceded by lactose hydrolysis.

Cheese primarily contains coagulated casein that retains fats, proteins, salts and fat-soluble vitamins.

Microbial action during ripening creates the aroma of each cheese.

Cheeses can be classified by process:

• Fresh: no ripening beyond lactic fermentation
• Mature: undergo additional fermentation and transformation
• Processed: blended, melted and emulsified cheeses, possibly with additives

Classified by fat content:

• Extra fat: ≥60%
• Fat: 45–60%
• Semi-fat: 25–45%
• Low-fat: 10–15%

Cheese production steps:

1. Milk pasteurisation (optional)
2. Inoculation with specific flora
3. Casein coagulation (acid or microbial)
4. Whey separation
5. Gel dehydration via syneresis
6. Salting and moulding
7. Ripening (with added microorganisms)

Caloric content ranges from 64 kcal/100g (skimmed) to 499 kcal/100g (processed).

Butter

According to the Spanish Food Code: “Butter is the fatty product obtained mechanically from milk or pasteurised cream” and contains a minimum of 80% fat.

Butter composition:

• Water: 12.5–16%
• Fat: 86.7–89.8%
• Protein: 1%
• Lactose: 4%
• Additives
• Natural colourants: xanthophylls
• Antifungals: sorbic acid
• Antioxidants: BHA
• Synergists: lactic acid, citric acid…

By-products Used in Food Industry

• Casein: used in baking to retain water and improve texture and preservation; also added to cereals and pasta.
• Whey proteins: Whey contains 70% lactose, 12% protein, 9% salts. Used as foaming agents in baking, chocolate, creams, desserts and ice creams. Also as thickeners and gelling agents in ready meals, sauces, meats and cheeses.
• Lactose: extracted from cheese whey by acid precipitation of proteins. The acidic solution is neutralised and evaporated to crystallise lactose.

Additives and Toxic Substances

Additives are prohibited in milk but allowed in dairy products. Cheese production commonly uses:

• Colourants: Mature cheese consumers prefer yellow tones; white implies freshness. Permitted colourants include beta-carotene (E-160) and riboflavin (E-101).
• Preservatives: stabilise protein or rennet precipitates.
• Rennet ferment: Originally from calves, now replicated via genetic technology to produce identical chymosin.
• Natamycin: an antibiotic to prevent mould on cheese rinds; limited to 5mm penetration.
• Other additives: Calcium chloride (20g/100L) to accelerate rennet coagulation.
• Phosphates: used in processed cheeses. Since phosphates accumulate, their intake must be monitored to avoid intestinal issues like diarrhoea.