Fermented and Non-Fermented Milk Products: Production and Processing

 

1. Introduction

Milk is a highly nutritious raw material and forms the base for a wide array of dairy products. Based on the use of microbial fermentation, milk products can be classified into two major categories:

• Fermented Milk Products: Products produced by the action of beneficial microorganisms on lactose (milk sugar), converting it into lactic acid and other metabolites.
• Non-Fermented Milk Products: Products made without microbial action; physical, thermal, or enzymatic processing is used instead.

Understanding the processing of these categories is essential for dairy industry professionals, product developers, and food technologists.

2. Fermented Milk Products

Definition

Fermented milk products are dairy products obtained by fermentation of milk using lactic acid bacteria (LAB), which cause thickening, acidification, flavor development, and increased shelf life.

2.1 Common Fermented Milk Products and Their Cultures

Product	Microbial Culture	Texture
Yogurt	Streptococcus thermophilus, Lactobacillus bulgaricus	Thick, smooth
Dahi (Indian curd)	Mesophilic or thermophilic LAB	Set or stirred
Kefir	Mixed culture of bacteria and yeasts (SCOBY)	Slightly fizzy
Lassi	Diluted yogurt with sugar or spices	Thin, drinkable
Buttermilk	Lactococcus lactis, Leuconostoc species	Sour, fluid
Acidophilus Milk	Lactobacillus acidophilus	Thin, probiotic
Viili/Filmjölk	Lactococcus lactis, Leuconostoc, yeasts	Ropy, mild

2.2 Processing of Fermented Milk Products

Step-by-Step General Process

1. Milk Standardization
• Adjust fat and solids-not-fat (SNF) levels using cream or skim milk powder.
2. Homogenization
• Ensures uniform fat distribution; pressure: 2000–2500 psi.
3. Pasteurization
• Typically at 85°C for 30 minutes or 90°C for 5 minutes.
• Denatures whey proteins for better gel formation.
4. Cooling to Inoculation Temperature
• 42°C for thermophilic cultures; 22–30°C for mesophilic cultures.
5. Inoculation
• Add 1–3% of starter culture under aseptic conditions.
6. Fermentation
• Maintain incubation temperature until pH drops to 4.4–4.6.
• Set yogurt: undisturbed fermentation in cups.
• Stirred yogurt: fermentation in tank followed by stirring.
7. Cooling and Storage
• Rapidly cool to 4°C.
• Store for up to 14–21 days under refrigeration.
8. Packaging
• Packed in cups, bottles, pouches, or bulk containers.

2.3 Important Factors in Fermented Product Processing

Factor	Effect
Incubation temperature	Determines speed and type of fermentation
Inoculum concentration	Affects acidification rate and flavor
Heat treatment	Impacts protein denaturation and viscosity
Homogenization	Improves consistency and body
Stabilizers (e.g., pectin, guar gum)	Prevents syneresis (whey separation)

3. Non-Fermented Milk Products

Definition

Non-fermented milk products are derived from milk without microbial fermentation. They rely on thermal, mechanical, or enzymatic processing for conversion.

3.1 Major Non-Fermented Milk Products

Product	Processing Method	Purpose
Pasteurized Milk	Thermal treatment at 72°C/15s (HTST)	Direct consumption
UHT Milk	135°C/2-4s followed by aseptic packaging	Long shelf-life
Sterilized Milk	110–120°C for 20–40 minutes	Ambient shelf-life
Flavored Milk	Addition of cocoa, fruit flavors, sugar	Beverage
Cream (Heavy/Light)	Centrifugal separation of milk	Fat-based product
Butter	Churning cream to concentrate milk fat	Spread
Ghee (Clarified Butter)	Boiling butter to remove water and solids	Cooking fat
Cheese (Non-fermented e.g., paneer)	Acid coagulation of milk	Soft cheese
Condensed Milk	Evaporation + sugar addition	Dessert ingredient
Evaporated Milk	60% water removed	Shelf-stable base
Milk Powder (SMP/WMP)	Spray drying or drum drying	Long-term storage
Ice Cream	Freezing an emulsified mix of milk, cream, sugar	Dessert

3.2 Key Processing Steps for Non-Fermented Products

A. Pasteurized Milk

• Standardize → Homogenize → Pasteurize (HTST or LTLT) → Cool → Pack

B. Butter and Ghee

• Cream Separation → Pasteurization → Churning → Butter
• Butter → Heating → Clarification → Ghee

C. Paneer

• Boil Milk → Add Acid (Citric/Lactic) → Coagulate → Drain → Press → Pack

D. Milk Powder

• Pasteurize → Concentrate → Spray Dry → Package in moisture-barrier pouches

E. Flavored Milk

• Mix milk + sugar + cocoa/fruit → Homogenize → Pasteurize → Bottle

F. Ice Cream

• Blend (milk, cream, sugar, stabilizer) → Pasteurize → Homogenize → Age → Freeze with air incorporation → Harden

4. Comparison: Fermented vs Non-Fermented Milk Products

Aspect	Fermented Products	Non-Fermented Products
Microbial Activity	Live bacteria or yeast involved	No live fermentation
Shelf Life	Shorter (7–21 days refrigerated)	Longer (up to months, depending on process)
Health Benefit	Probiotics, improved digestion	High in nutrients, no probiotics
pH	Low (4.0–4.6) due to lactic acid	Neutral (~6.7)
Texture	Thickened or gel-like	Ranges from liquid to solid
Flavor	Tart, sour, cultured taste	Sweet, creamy, or neutral
Applications	Beverages, breakfast, therapeutic foods	Cooking, baking, beverages, spreads

5. Quality and Safety Considerations

Parameter	Control Measures
Microbiological Safety	Pasteurization, hygiene, culture purity
Sensory Quality	Standardization, fresh ingredients, storage
pH and Acidity	Controlled fermentation or acid addition
Texture and Viscosity	Homogenization, stabilizers, correct formulation
Shelf Life	Packaging, refrigeration, UHT processing

6. Conclusion

The dairy industry thrives on the versatility of milk to produce a broad spectrum of fermented and non-fermented products. While fermented products leverage the health benefits and flavor complexity from beneficial microbes, non-fermented products rely on thermal, mechanical, and chemical transformations to meet consumer needs for nutrition, convenience, and culinary diversity.

Understanding the differences in processing requirements and quality control parameters is key for successful dairy product development, safety assurance, and market competitiveness.