Milk Processing Operations

1. Milk Reception (Procurement & Intake)

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Key Activities:

• Weighing / Volume measurement
• Sampling & Quality Testing
• Fat %
• SNF (Solids-Not-Fat)
• Acidity
• Microbial load
• Organoleptic evaluation (smell, color)
• Equipment:

Weighing scale

Lactometer

Milk analyzer

2. Filtration / Clarification

• Purpose:

Remove physical impurities:

Dust

Hair

Dirt particles

• Methods:

Cloth filtration

Centrifugal clarifier

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3. Cooling and Storage (Chilling)

Objective:

• Reduce temperature to ≤ 4°C to inhibit microbial growth

Equipment:

• Bulk Milk Cooler (BMC)
• Plate Heat Exchanger (PHE)
• Storage silos

4. StandardizationStandardization of milk

is the process of adjusting the fat and SNF content to meet legal or product specifications (e.g., toned milk, double toned milk).

One of the simplest calculation tools used in dairy plants is the Pearson Square Method

Purpose:

• Adjust fat and SNF to desired levels

Method:

• Separation into:
• Cream
• Skim milk
• Recombination in required proportions

Examples:

• Toned milk
• Double toned milk
• Full cream milk

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Pearson Square Method (Concept)

It is a graphical calculation technique used to determine how much of two components with different fat percentages must be mixed to obtain a desired fat percentage.

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5. Homogenization

Objective:

• Reduce fat globule size to prevent creaming

Process:

• High pressure (150–250 bar)
• Fat globules broken into smaller uniform sizes

Result:

• Uniform texture
• Improved taste and stability

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Determination of Homogenization Efficiency by Farrell Index Method

Principle

• Homogenization reduces fat globule size and ensures uniform distribution of fat throughout milk.
• If homogenization is inefficient, fat globules rise and form a cream layer during storage.

The Farrell Index (FI) measures the difference in fat concentration between:

• Top layer (cream-rich)
• Bottom layer (skim-rich)

Procedure

Step 1: Sample Preparation

• Take fresh homogenized milk sample
• Mix thoroughly

Step 2: Filling Cylinder

• Fill a graduated glass cylinder (e.g., 100 ml)
• Avoid air bubbles

Step 3: Storage

• Keep undisturbed at:
• 4–10°C for ~24 hours

Step 4: Sampling

• Carefully withdraw:
• Top layer sample (upper portion)
• Bottom layer sample (lower portion)

Step 5: Fat Determination

• Determine fat % using:
• Gerber method (common)
• Babcock method

Step 6: Calculation

• Apply formula:
• FI=Fat (Top)Fat (Bottom)

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Example�Fat (Top) = 3.2% �Fat (Bottom) = 3.0% �FI=3.2/3.0=1.07�Interpretation: Good homogenization�

6. Heat Treatment (Pasteurization / Sterilization)

Pasteurization is a heat treatment process applied to a product with the aim of minimizing possible health hazards arising from pathogenic microorganisms associated with milk, by applying heat at such temperatures and for such periods as to destroy harmful organisms, with minimal chemical, physical, and organoleptic changes in the product.

It Causes cent per cent destruction of pathogens.

Types:

(A) Pasteurization

• LTLT: 63°C for 30 min
• HTST: 72°C for 15 sec

(B) UHT (Ultra High Temperature)

• 135–150°C for 2–5 sec

Purpose:

• Destroy pathogens
• Extend shelf life

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Determination of Pasteurization Efficiency by Alkaline Phosphatase (ALP) Test

Principle

• Milk contains a natural enzyme called alkaline phosphatase (ALP).
• This enzyme is more heat-resistant than most pathogenic bacteria.
• Proper pasteurization (e.g., 72°C for 15 sec) destroys ALP.

Therefore:

• ALP absent → Proper pasteurization
• ALP present → Inadequate pasteurization or contamination

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Chemical Basis

ALP hydrolyses substrates like phenolphthalein monophosphate:

Phenolphthalein phosphate----ALP----→ Phenolphthalein+Phosphate

Phenolphthalein turns pink in alkaline medium

No color = no enzyme activity

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7. Cooling After Heat Treatment

Objective:

• Quickly cool milk to ≤ 4°C

Importance:

• Prevent bacterial regrowth

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8. Packaging

Types:

• Plastic pouches
• Glass bottles
• Tetra packs

Requirements:

• Hygienic conditions
• Airtight sealing

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9. Storage and Distribution

Key Points:

• Maintain cold chain (≤ 4°C)
• Use refrigerated vehicles
• Timely delivery

Milk Reception

↓

Filtration / Clarification

↓

Cooling (Chilling)

↓

Standardization

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Homogenization

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Pasteurization / UHT

↓

Cooling

↓

Packaging

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Storage & Distribution

Flow Chart of Milk Processing

Key Objectives of Milk Processing

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Ensure safety (pathogen destruction)

Improve shelf life

Maintain nutritional quality

Provide uniform composition

Enhance consumer acceptability