ICAR AIEEA-PG Market Milk Processing: practice questions

ICAR AIEEA-PG: Dairy Science (group 16) and Dairy Technology (group 17) · India · NTA for ICAR

Original practice questions written to the published syllabus · not past papers

10worked here, free

66written to this exam in this subject

14syllabus units

What this subject covers

From reception to the consumer pack: clarification, separation, standardisation, homogenisation, pasteurisation, ESL and UHT, and special milks.

In the exams: ICAR AICE subject 37 Unit 1; ICAR AIEEA-PG group 17 Unit I (processing of fluid milk, centrifugal separation and bactofugation, HACCP in fluid milk processing); GATE XL-U Section 3

Milk reception, testing and payment
Chilling and storage of raw milk
Clarification and bactofugation
Cream separation and separator efficiency
Standardisation calculations: Pearson square and algebraic methods
Homogenisation: theory and efficiency
Pasteurisation: LTLT, HTST, holding time and flow diversion
Extended shelf life milk
UHT processing: direct and indirect systems
In-container sterilisation
Toned, double-toned, recombined, reconstituted, flavoured and fortified milks
Lactose-free and other special milks
HACCP in fluid milk processing
Distribution and retail of fluid milk

What ICAR AIEEA-PG asks from it

ICAR AIEEA-PG — Dairy Technology (group 17) and Dairy Science (group 16)

Group 17 Unit I names processing of fluid milk, automatic process control, HACCP in fluid milk, centrifugal separation and bactofugation, and membrane processing; Unit II names the homogeniser (triplex pump, care), pasteuriser construction and HTST, and reaction kinetics. Group 16 adds bacteriology of thermisation, pasteurisation, boiling, sterilisation, UHT and bactofugation. Expect direct MCQs and short calculations: Pearson square, separator mass balance, regeneration, time-temperature standards, phosphatase test.

Where the 66 questions fall

How our questions for ICAR AIEEA-PG spread across the units of Market Milk Processing. Difficulty: 21 easy, 41 medium, 4 hard.

Pasteurisation: LTLT, HTST, holding time and flow diversion	11
Milk reception, testing and payment	8
Cream separation and separator efficiency	6
Toned, double-toned, recombined, reconstituted, flavoured and fortified milks	6
Standardisation calculations: Pearson square and algebraic methods	5
Homogenisation: theory and efficiency	5
HACCP in fluid milk processing	5
Distribution and retail of fluid milk	5
Chilling and storage of raw milk	4
Clarification and bactofugation	4
UHT processing: direct and indirect systems	3
In-container sterilisation	2
Extended shelf life milk	1
Lactose-free and other special milks	1

10 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

1 · Milk reception, testing and payment · easy

A tanker delivers 2,000 L of milk of density 1.030 kg/L with 3.8% fat. How many kilograms of fat does it contain?

73.8 kg
78.3 kg
7,828 kg
76.0 kg

Answer and working

B. 78.3 kg

Mass = 2000 × 1.030 = 2060 kg; fat = 2060 × 0.038 = 78.3 kg. 76.0 kg treats litres as kilograms; 73.8 kg divides by density instead of multiplying; 7,828 kg forgets to divide the percentage by 100.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

2 · Pasteurisation: LTLT, HTST, holding time and flow diversion · hard

An HTST holding tube of 50 mm internal diameter carries 10,000 L/h. Flow is laminar, so the fastest particle moves at twice the mean velocity. What tube length gives the fastest particle 15 s?

25.5 m
42.4 m
169.8 m
21.2 m

Answer and working

B. 42.4 m

Mean velocity = (10/3600 m³/s) ÷ (π × 0.05² ÷ 4) = 1.415 m/s; fastest = 2.829 m/s; length = 2.829 × 15 = 42.4 m. 21.2 m uses the mean velocity; 25.5 m applies the turbulent-flow factor; 169.8 m puts the radius in place of the diameter in πd²/4, which quarters the area and quadruples the velocity.

Further reading: Tetra Pak, Dairy Processing Handbook

3 · Milk reception, testing and payment · medium

The 'natural' titratable acidity of fresh milk (commonly about 0.13–0.15% as lactic acid for cow milk) arises mainly from:

Lactic acid made by bacteria in the udder before the cow is milked
Fatty acids released by lipase during the first hour after milking
Ascorbic acid added by the cow's metabolism to stabilise the milk
Casein, phosphates, citrates and CO2 rather than lactic acid

Answer and working

D. Casein, phosphates, citrates and CO2 rather than lactic acid

Fresh milk contains almost no lactic acid; the titratable acidity comes from the buffering of casein, phosphates, citrates and CO2. Developed acidity is lactic acid added by bacterial fermentation.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

4 · Clarification and bactofugation · easy

What does a milk clarifier remove?

Lactose, which crystallises in the bowl and is discharged
Dissolved salts, which pass through a membrane in the bowl
Dirt, leucocytes, udder cells and other dense particles
Fat globules, which leave through a separate cream outlet

Answer and working

C. Dirt, leucocytes, udder cells and other dense particles

A clarifier has one outlet and removes dense particles into the sediment space. A separator has a cream outlet; neither removes lactose or dissolved salts.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

5 · Homogenisation: theory and efficiency · medium

A homogeniser pump commonly uses three pistons (a triplex pump) in order to:

Treat three different products at once through separate valves
Raise the milk temperature in three steps to pasteurisation
Divide the fat into three size fractions for standardisation
Smooth the flow and pressure delivered to the homogenising valve

Answer and working

D. Smooth the flow and pressure delivered to the homogenising valve

Three pistons out of phase reduce pulsation. A homogeniser does not heat or fractionate fat.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

6 · Pasteurisation: LTLT, HTST, holding time and flow diversion · medium

Why does the holding tube of an HTST pasteuriser slope upward in the direction of flow?

To let cream separate before cooling
To expel air and keep the tube completely full
To drain the tube completely during operation
To slow the milk down so it is held longer

Answer and working

B. To expel air and keep the tube completely full

An upward slope pushes air out and ensures the full volume is used. Draining is done at shutdown, not during operation.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

7 · Toned, double-toned, recombined, reconstituted, flavoured and fortified milks · easy

Recombined milk is made from:

Skim milk powder, milk fat and water, homogenised together
Buffalo milk diluted with water to lower the fat
Fresh skim milk and fresh cream mixed in the tank
Whole milk powder and water only, without homogenisation

Answer and working

A. Skim milk powder, milk fat and water, homogenised together

Recombined = SMP + milk fat (AMF or butter oil) + water, homogenised. Powder + water alone is reconstituted milk; diluting with water is adulteration.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

8 · Toned, double-toned, recombined, reconstituted, flavoured and fortified milks · medium

Why is carrageenan added to chocolate milk?

It lowers the pasteurisation temperature needed for flavoured milk
It gels weakly with milk protein and keeps the cocoa suspended
It sweetens the milk so that less sugar is needed in the formulation
It colours the milk brown so that less cocoa powder needs to be used

Answer and working

B. It gels weakly with milk protein and keeps the cocoa suspended

Low levels of carrageenan interact with casein to suspend cocoa. It is not a sweetener or colour.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

9 · HACCP in fluid milk processing · medium

In a fluid milk HACCP plan, the alkaline phosphatase test on finished milk is best classed as:

Verification that the pasteurisation CCP is working
A corrective action after deviation
Monitoring of the CCP in real time
A prerequisite programme for cleaning

Answer and working

A. Verification that the pasteurisation CCP is working

Phosphatase results come after the event and confirm the system works, which is verification. Monitoring is the continuous temperature record.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

10 · Distribution and retail of fluid milk · easy

Why is UHT milk valuable where cold chains are weak?

It needs no refrigeration until the pack is opened
It never develops any change in flavour
It needs no refrigeration even after the pack is opened
It is cheaper to produce than pasteurised milk

Answer and working

A. It needs no refrigeration until the pack is opened

UHT is ambient-stable unopened but perishable once opened. It is not necessarily cheaper and does change in flavour during storage.

Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology

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