GATE — Agricultural Engineering (AG) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersMoisture, drying, parboiling, milling, cleaning, size reduction and conveying of grains, pulses and oilseeds.
In the exams: GATE AG Section 6 (~14 marks a year 2019–26; psychrometry in all 8 papers, rice milling in 6 of 8); ICAR AIEEA-PG Unit VI; ICAR AICE subject 41; NCEES PE processing; PRC ABE bioprocess; ASRB NET ASPE
GATE — Agricultural Engineering (AG)
Section 6 carries roughly 14 marks a year and is mostly numerical: humidity ratio, humid volume and adiabatic mixing of air streams (asked in most recent papers); rice milling, husking coefficients and parboiling effects (most papers); wet/dry-basis conversion and water to add or remove; drying time and EMC; separation and screen effectiveness; Rittinger, Kick and Bond energy; ball-mill critical speed; bucket elevator speed. Expect two-mark questions that chain three or more steps, and conceptual one-mark items on parboiling and drying mechanisms.
How our questions for GATE spread across the units of Post-Harvest Engineering of Cereals, Pulses & Oilseeds. Difficulty: 15 easy, 21 medium, 19 hard.
| Psychrometry and properties of air | 9 | |
| Paddy and rice milling: husking, whitening, polishing and yields | 7 | |
| Drying theory: constant and falling rate periods | 6 | |
| Parboiling and hydrothermal treatment | 6 | |
| Size reduction: Rittinger, Kick and Bond laws | 6 | |
| Moisture content: wet and dry basis | 4 | |
| Cleaning, grading and screening effectiveness | 4 | |
| Conveying: belt, bucket, screw and pneumatic | 4 | |
| Thin-layer drying models | 3 | |
| Equilibrium moisture content and sorption isotherms | 2 | |
| Grain dryers: bin, LSU, recirculating, fluidised-bed and solar | 2 | |
| Wheat milling | 1 | |
| Oil expression and solvent extraction | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
How much water must be added to 500 kg of wheat at 11% wet-basis moisture to temper it to 16% wet basis?
D. 29.8 kg
Dry matter = 500 × 0.89 = 445 kg. Final mass = 445/0.84 = 529.76 kg, so water to add = 29.8 kg. 25 kg (5% of 500) ignores that the total mass grows as water is added; 28.1 kg divides by the initial rather than the final (1 − M). 22.3 kg multiplies the dry matter by the 5-point rise (445 × 0.05).
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
One tonne of maize at 30% moisture (dry basis) is dried to 12% moisture (wet basis). The water removed is closest to
D. 126 kg
Dry matter = 1000/(1 + 0.30) = 769.2 kg. Final mass at 12% wb = 769.2/0.88 = 874.1 kg. Water removed = 1000 − 874.1 = 125.9 kg. 180 kg subtracts percentages on mixed bases; 231 kg is the total water initially present, as if dried to zero moisture. 205 kg treats the initial 30% as wet basis.
Further reading: Chakraverty, Post Harvest Technology of Cereals, Pulses and Oilseeds
Air is at 30 °C and 50% RH (p_vs at 30 °C = 4.246 kPa). Given saturation pressures of 2.064 kPa at 18 °C and 2.198 kPa at 19 °C, its dew point is closest to
A. 18.4 °C
p_v = 0.5 × 4.246 = 2.123 kPa. The dew point is where p_vs = p_v: interpolating, 18 + (2.123 − 2.064)/(2.198 − 2.064) = 18.4 °C. The dew point equals the dry-bulb (30 °C) only at 100% RH. 18.0 °C takes the lower table value without interpolating; 15.0 °C halves the dry-bulb temperature.
Further reading: ASABE D271
A tray holds 50 kg of dry solid on 2 m² and dries at a constant rate R_c = 1.5 kg/m²·h down to the critical moisture X_c = 0.6 (db); the rate then falls linearly to zero at X_e = 0.05. The falling-rate time from 0.6 to 0.15 kg/kg (db) is closest to
A. 15.6 h
t_f = [W_s(X_c − X_e)/(A R_c)] ln[(X_c − X_e)/(X − X_e)] = (50 × 0.55/3) × ln(0.55/0.10) = 9.167 × 1.7047 = 15.63 h. Dropping the log term gives 9.2 h; using total rather than free moisture in the log gives 12.7 h; 25.6 h is the total including the constant-rate period.
Further reading: Earle, Unit Operations in Food Processing
The LSU dryer is best described as a
B. continuous mixed-flow column dryer with alternate rows of inverted-V inlet and outlet ducts
Grain flows down by gravity past rows of inverted-V channels connected alternately to the hot-air plenum and the exhaust, and a fluted discharge roll sets the flow rate.
Further reading: Chakraverty, Post Harvest Technology of Cereals, Pulses and Oilseeds
Compared with raw rice from the same paddy, parboiled rice usually gives
A. higher head rice yield
Gelatinised starch fills voids and heals cracks, hardening the kernel so it resists breakage in the mill. So parboiled rice gives fewer broken kernels than raw rice.
Further reading: Chakraverty, Post Harvest Technology of Cereals, Pulses and Oilseeds
Broken rice kernels are separated from head rice in a modern mill mainly by
B. indented cylinder length graders and sieves
Brokens are shorter, so they lodge in the indents of a rotating cylinder and are lifted out. Gravity tables separate by density and aspirators by terminal velocity.
Further reading: Chakraverty, Post Harvest Technology of Cereals, Pulses and Oilseeds
An indented cylinder (trieur) separates particles mainly by
D. length
Short particles lodge in the indents and are lifted into a trough; long ones slide out. Density is exploited by gravity tables and texture by velvet rolls.
Further reading: Chakraverty, Post Harvest Technology of Cereals, Pulses and Oilseeds
A crusher needs 10 kW to reduce a material from 20 mm to 5 mm. Assuming Kick's law, the power to reduce the same throughput from 20 mm to 2.5 mm is
B. 15.0 kW
Kick: E ∝ ln(L₁/L₂). Ratio = ln 8/ln 4 = 1.50, so P = 15.0 kW. Rittinger would give 23.3 kW and Bond 18.3 kW; doubling the power assumes energy proportional to size change.
Further reading: Earle, Unit Operations in Food Processing
Which size-reduction law is generally considered most applicable to fine grinding?
A. Rittinger's law
Rittinger relates energy to new surface area, which dominates in fine grinding. Kick fits coarse crushing; Bond lies between; Stokes' law concerns settling.
Further reading: Earle, Unit Operations in Food Processing
Ten here, 55 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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