Methods of Milking; Milking is the process of extracting milk from the mammary gland (udder) of dairy animals. Efficient milking ensures good milk yield, udder health, and hygiene.

🔹 1. Hand Milking

a) Full Hand Milking (Recommended Method)

• The entire hand (fingers and thumb) is used to press the teat from top to bottom.
• Milk is squeezed out, not pulled.
• Prevents injury to teats and udder.
• Advantages:
  • Hygienic
  • Comfortable for animal
  • Recommended for buffaloes and cows

b) Stripping

• Milk is pulled down by sliding fingers from top to bottom.
• Not recommended due to risk of teat injury.
• Used only to empty residual milk after normal milking.

c) Knuckling

• Teat is pressed using finger joints (knuckles).
• Harmful: May damage teat canal and lead to mastitis.
• Not advised.

2. Machine Milking

• Used in commercial dairy farms with large herd size.
• Works on vacuum and pulsation principle.
• Mimics suckling of calf by creating intermittent vacuum and release.

3. Wet vs. Dry Milking

🔹 Milking Principles

• Follow regular timing (interval of 12 hrs).
• Ensure clean hands and utensils.
• Start milking soon after let-down reflex (oxytocin release).
• Avoid stress to the animal.
• Strip the teats to check for mastitis.

Key Points for Exam

• Best method: Full-hand milking
• Machine milking: Based on vacuum principle
• Harmful method: Knuckling
• Let-down reflex: Stimulated by oxytocin
• Dry milking is more hygienic than wet milking

Thermal Processing of Milk

Purpose of Thermal Processing

• Most heat-resistant pathogen: Bacillus tuberculosis (Index organism).
• Key pathogens in milk: Tubercle bacilli, Typhus, Coliforms, Coxiella burnetii (Q-fever).

Types of Heat Treatments

1. Pasteurization

Definition: Heat treatment of milk to kill pathogens without affecting nutritional quality, followed by rapid cooling and refrigeration.

Types:

• LTLT (Low Temp Long Time):
  • Temp: 63°C
  • Time: 30 min
  • Method: Batch process in jacketed vats (200–1000 L capacity)
  • Suitable for: Small-scale operations

• HTST (High Temp Short Time):
  • Temp: 72°C
  • Time: 15 seconds
  • Method: Continuous flow in plate heat exchangers
  • Suitable for: Large-scale (≥5000 L/hr)

🔹 2. Thermization

• Purpose: Temporary heat treatment when immediate pasteurization isn’t possible.
• Temp: 63–65°C
• Time: 15 sec
• Benefit: Inhibits bacterial growth; spores revert to vegetative form for later destruction in pasteurization.

3. Ultra-pasteurization

• Temp: 115–130°C
• Time: 2–4 sec
• Shelf life: Extended by 15–30 days
• Requires: Aseptic packaging, strict hygiene, cold storage (<4°C)

4. Ultra High Temperature (UHT)

• Temp: 135–150°C
• Time: 1–6 sec
• Method: Direct (steam injection) or Indirect (heat exchangers)
• Aseptic packaging: Special multilayer containers
• Shelf life: 2–6 months without refrigeration

5. Sterilization

• Temp: 115–121°C
• Time: 20–30 min
• Containers: Glass bottles or tin cans (200–400 g)
• Method: In-container (batch or continuous via autoclaves/hydrostatic towers)
• Result: Kills all microbes including spores.

6. Microwave Heating

• Frequency: 915 or 2450 MHz
• Mechanism: Water dipole oscillation produces heat internally
• Benefits:
  • Fast, uniform heating
  • Reduced lag in heat penetration
• Challenges:
  • Surface cooling due to evaporation
  • Uneven absorption in frozen or high-salt foods

✅ Important Points to Remember

• Bacillus tuberculosis: Index organism for pasteurization.
• HTST is energy-efficient due to regeneration.
• Thermization is pre-treatment before pasteurization.
• UHT milk needs no refrigeration.
• Sterilization gives longest shelf life but may alter taste.
• Microwave heating is rapid but less uniform.