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 papersMeasuring and modelling how foods flow, deform, break and transfer heat: rheometry of fluids and gels, viscoelasticity, texture profile analysis, and thermal, electrical and optical properties. Agricultural Engineering's engineering-properties-biomaterials covers size, shape, density and friction of grains and produce; this subject goes deeper into processed foods and their measurement.
In the exams: ICAR AIEEA-PG Code 18 Units I–II (physical properties of foods; engineering properties of food materials); ICAR AICE 37 Unit 5 (rheology of dairy foods)
GATE — Engineering Sciences (XE), Section G Food Technology
Section 4 names flow of Newtonian fluids and heat transfer; Section 1 names starch gelatinisation and retrogradation. Rheology and physical properties appear as the inputs to flow and heat-transfer calculations (viscosity, power-law parameters, thermal properties) and in reasoning about starch and gel behaviour.
GATE — Life Sciences (XL), Section U Food Technology
Same scope as XE-G; property values and flow-behaviour reasoning are tested through processing questions.
How our questions for GATE spread across the units of Physical Properties, Rheology & Texture of Foods. Difficulty: 7 easy, 16 medium, 7 hard.
| Fundamentals of rheology: stress, strain and viscosity | 6 | |
| Newtonian and non-Newtonian fluids: power-law, Herschel-Bulkley and Casson models | 6 | |
| Electrical and dielectric properties of foods | 6 | |
| Thermal properties: specific heat, thermal conductivity and diffusivity of foods | 4 | |
| Rheology of doughs and dairy gels | 4 | |
| Rotational and capillary viscometry | 3 | |
| Physical properties of foods: density, porosity and particle size distribution | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Porosity strongly lowers the thermal conductivity of a dry food mainly because
D. air in the pores conducts heat very poorly
Air (about 0.025 W/m K) is a good insulator, so porous foods conduct poorly.
Further reading: Sahin and Sumnu, Physical Properties of Foods
A food contains 75 % water, 20 % protein and 5 % fat. Taking component cp values of 4.18, 1.6 and 2.0 kJ/kg K, its specific heat by mass-fraction weighting is
B. 3.56 kJ/kg K
cp = 0.75 × 4.18 + 0.20 × 1.6 + 0.05 × 2.0 = 3.56. 7.78 adds the component values; 2.59 is their plain average; 4.18 is water alone.
Further reading: Singh and Heldman, Introduction to Food Engineering
A food has k = 0.50 W/m K, ρ = 1,050 kg/m³ and cp = 3,600 J/kg K. Its thermal diffusivity is closest to
D. 1.32 × 10⁻⁷ m²/s
α = k/(ρcp) = 0.50/(1,050 × 3,600) = 1.32 × 10⁻⁷ m²/s. Using cp in kJ gives a value 1,000 times too large; the other two rearrange the formula wrongly.
Further reading: Singh and Heldman, Introduction to Food Engineering
Milk has dynamic viscosity 2.0 mPa s and density 1,030 kg/m³. Its kinematic viscosity is closest to
C. 1.94 mm²/s
ν = μ/ρ = 0.002/1,030 = 1.94 × 10⁻⁶ m²/s = 1.94 mm²/s (cSt). 2.06 multiplies; 515 inverts; 0.002 confuses units.
Further reading: Steffe, Rheological Methods in Food Process Engineering
A purée follows τ = Kγ̇ⁿ with K = 10 Pa sⁿ and n = 0.4. Its apparent viscosity at 50 s⁻¹ is closest to
B. 0.96 Pa s
η = Kγ̇^(n−1) = 10 × 50^(−0.6) = 0.96 Pa s. 47.8 Pa s is the shear stress; 2.09 uses exponent −n; 0.24 is the value at 500 s⁻¹.
Further reading: Steffe, Rheological Methods in Food Process Engineering
On a log–log plot of shear stress against shear rate for a power-law fluid, the slope equals
A. the flow behaviour index n
log τ = log K + n log γ̇: slope n, intercept log K.
Further reading: Steffe, Rheological Methods in Food Process Engineering
The yield stress of a sauce is best measured without wall-slip errors using
B. a vane geometry rotated slowly
The vane shears within the sample, avoiding slip at smooth walls and disturbing the structure little.
Further reading: Steffe, Rheological Methods in Food Process Engineering
A shear-thinning salad dressing is desirable because it
A. is thick at rest but thins when poured
Apparent viscosity falls under the high shear of pouring and spreading but is high at rest, keeping herbs suspended.
Further reading: Rao, Rheology of Fluid, Semisolid, and Solid Foods
Single-point readings from a spindle ('Brookfield-type') viscometer on a non-Newtonian sauce are
B. comparable only under identical test conditions
The shear rate is undefined for non-Newtonian samples, so readings are empirical apparent viscosities.
Further reading: Steffe, Rheological Methods in Food Process Engineering
Using P = 2πfε0ε″E² with f = 2.45 GHz, ε0 = 8.854 × 10⁻¹² F/m, ε″ = 15 and E = 1,000 V/m, the power absorbed per unit volume is closest to
C. 2.04 × 10⁶ W/m³
P = 2π × 2.45 × 10⁹ × 8.854 × 10⁻¹² × 15 × 10⁶ = 2.04 × 10⁶ W/m³. Omitting 2π gives 3.25 × 10⁵; using E instead of E² gives a value 1,000 times smaller; 1.06 × 10⁷ uses the dielectric constant ε′ (about 78) instead of the loss factor ε″.
Further reading: Datta and Anantheswaran, Handbook of Microwave Technology for Food Applications
Ten here, 30 in the app. The Laisha app has every practice question we have written to GATE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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