ICAR AICE-JRF/SRF Market Milk Processing: practice questions

1 · Clarification and bactofugation · medium

By Stokes' law, if a particle's diameter is doubled and all else is unchanged, its separation velocity becomes:

1. 4 times greater
2. Half as great
3. 2 times greater
4. 8 times greater

2 · Cream separation and separator efficiency · hard

Warming milk from 10 °C to 45 °C lowers its viscosity from 2.5 mPa·s to 1.0 mPa·s. Ignoring changes in density, by what factor does the rising velocity of a fat globule increase (Stokes' law)?

1. 4.5
2. 2.5
3. 0.4
4. 6.25

3 · 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?

1. 25.5 m
2. 42.4 m
3. 169.8 m
4. 21.2 m

4 · UHT processing: direct and indirect systems · hard

Using F0 = t (min) × 10^((T − 121.1) ÷ 10), what is the F0 of 4 seconds at 140 °C?

1. 4.21 min
2. 310.5 min
3. 5.17 min
4. 0.13 min

5 · Milk reception, testing and payment · hard

Why does a volumetric flow meter at tanker reception need an air eliminator?

1. Air reacts with milk fat in the meter and causes oxidised flavour very rapidly
2. Air bubbles block the meter, so flow stops and the tanker cannot be emptied
3. Air dissolves into milk under pressure and raises its density reading by error
4. Entrained air is counted as milk, so the meter over-reads

6 · Chilling and storage of raw milk · hard

Activation of the lactoperoxidase system to preserve raw milk involves adding:

1. Nisin and lysozyme to stop spore germination in milk held at ambient temperature
2. Sodium bicarbonate to neutralise acid as it forms during transport to the plant
3. Small amounts of thiocyanate and a hydrogen peroxide source such as percarbonate
4. Large amounts of formalin to kill all bacteria until the milk reaches the plant

7 · Homogenisation: theory and efficiency · medium

Why must raw milk be pasteurised immediately after homogenisation?

1. Homogenised milk loses its casein, which must be restored by heating
2. Homogenisation adds air, which only pasteurisation can remove from milk
3. Native lipase attacks the exposed fat and turns the milk rancid fast
4. Homogenised raw milk clots at once, and heating redissolves the clot

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

Holding time in an HTST plant must be met by:

1. The fastest-moving particle, not the average particle
2. The particle at the inlet of the regenerator
3. The average particle, measured by dividing volume by flow
4. The slowest particle near the tube wall

9 · Extended shelf life milk · medium

Why is the cream fraction heat-treated separately rather than microfiltered in the MF route to ESL milk?

1. Heat makes the cream sweeter, which improves the milk flavour
2. Cream passes through any membrane, so filtration does nothing
3. Cream contains no bacteria, so it needs no treatment at all
4. Fat globules are bacteria-sized and would be retained with them

10 · HACCP in fluid milk processing · medium

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

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