GATE — Life Sciences (XL), Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersThe dairy course taught inside food technology degrees: milk as a raw material, fluid-milk processing, the main dairy products, and dairy ingredients (powders, whey and milk proteins) used across the food industry. For depth in dairy chemistry, microbiology and plant engineering see the Dairy Technology track; for Indian traditional dairy products and FSSAI dairy standards see Veterinary's milk-products-technology.
In the exams: GATE XE-G and XL-U Section 3 (milk and milk products processing: pasteurisation, sterilisation, cream, butter, ghee, ice cream, cheese, milk powder); ICAR AIEEA-PG Code 18 Unit III; ICAR AICE 35.a Unit 3
GATE — Engineering Sciences (XE), Section G Food Technology
Section 3 lists milk and milk products processing: pasteurisation, sterilisation, cream, butter, ghee, ice cream, cheese and milk powder. Expect conceptual items on HTST and UHT, the phosphatase test, homogenisation and Stokes' law, churning, rennet action, yoghurt cultures and spray drying, and numerical-answer items on standardisation, cream separation, regeneration efficiency, overrun, butter and powder yields.
GATE — Life Sciences (XL), Section U Food Technology
Same Section 3 content as XE-G, often framed through chemistry and microbiology: casein micelles and κ-casein cleavage, isoelectric precipitation, whey protein denaturation, protocooperation in yoghurt, lactose crystallisation and Maillard browning in dairy products.
How our questions for GATE spread across the units of Dairy Science & Technology for Food Technologists. Difficulty: 11 easy, 29 medium, 7 hard.
| Pasteurisation, UHT and sterilised milks | 7 | |
| Clarification, separation and standardisation | 6 | |
| Cheese: coagulation, cheddar and mozzarella principles | 6 | |
| Homogenisation | 5 | |
| Ice cream and frozen desserts | 5 | |
| Milk powders and infant formula basics | 5 | |
| Cream, butter and ghee | 4 | |
| Condensed and evaporated milk | 4 | |
| Fermented milks | 3 | |
| Milk reception, quality testing and platform tests | 1 | |
| Whey and milk-protein ingredients | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
By Stokes' law, if the diameter of a fat globule doubles, its rising velocity
A. Increases four times
Velocity is proportional to the square of the diameter, so doubling it gives 2² = 4 times the velocity. Proportional, inverse and no change are the usual slips.
Further reading: Tetra Pak, Dairy Processing Handbook
1000 kg of milk at 4.0% fat is separated into cream of 40% fat and skim of 0.05% fat. The mass of cream is about
D. 98.9 kg
Cream = 1000 × (4.0 − 0.05) ÷ (40 − 0.05) = 98.9 kg. 100 kg assumes skim has no fat (1000 × 4 ÷ 40); 901 kg is the skim; 90.1 kg is a decimal slip on the skim.
Further reading: Tetra Pak, Dairy Processing Handbook
Milk is separated warm, commonly at 40–50 °C or above, mainly because
D. Fat is liquid and viscosity is lower
Warm milk has liquid fat and lower viscosity, so globules separate faster and more completely. Separation temperatures are not a kill step, and lactose and casein do not change in these ways.
Further reading: Tetra Pak, Dairy Processing Handbook
The flow diversion valve of an HTST pasteuriser
C. Diverts under-heated milk
If the temperature at the end of the holding tube falls below the legal minimum, the valve diverts the milk back to the balance tank for reheating. It does not standardise, control fillers or de-aerate.
Further reading: Tetra Pak, Dairy Processing Handbook
Homogenisation of milk mainly
B. Reduces fat globule size
It forces milk through a narrow gap at high pressure, breaking globules to below about 1–2 µm. It is not a kill step, does not remove fat and does not change lactose.
Further reading: Tetra Pak, Dairy Processing Handbook
Homogenisation pressures for milk in the first stage are commonly in the range of
C. 10–25 MPa
First-stage pressures of roughly 10–25 MPa (100–250 bar) are common. 100–250 MPa is the range of high-pressure processing, and kPa values are far too low.
Further reading: Tetra Pak, Dairy Processing Handbook
Chymosin coagulates milk by cleaving
C. κ-casein
Chymosin specifically cleaves κ-casein at Phe105–Met106, removing the stabilising caseinomacropeptide so the micelles aggregate with calcium. It does not act on the other proteins or on lactose.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Ice cream kept in a shop freezer whose temperature cycles develops a coarse, icy texture because
B. Ice recrystallisation
Heat shock melts the smallest ice crystals and refreezes the water onto larger ones, coarsening the texture. Lactose crystallisation gives sandiness, overrun falls rather than rises, and fat does not leave.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Most milk powder is made by
A. Spray drying
Concentrated milk is atomised into hot air in spray driers, usually with fluid-bed stages. Drum drying is an older method for some products, and freeze or sun drying are not used for milk powder at scale.
Further reading: Tetra Pak, Dairy Processing Handbook
100 L of ice cream mix gives 190 L of ice cream. The overrun by volume is
A. 90%
Overrun = (190 − 100) ÷ 100 × 100 = 90%. 190% is the final volume as a percentage; 47% divides 90 by 190; 53% is the mix share of the ice cream.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
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