GATE — Agricultural Engineering (AG) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersKeeping fruits and vegetables alive and saleable after harvest: cooling, handling, packhouses, controlled atmospheres and processing.
In the exams: GATE AG Section 6 (processing of fruits, vegetables and spices; CA/MA storage); ICAR AICE subject 41
GATE — Agricultural Engineering (AG)
Section 6 names processing of fruits, vegetables and spices and storage systems including CA/MA. Expect numerical items on moisture balances in drying, water removed, respiration heat and refrigeration load, half-cooling time and seven-eighths cooling, juice concentration and blending balances, and gas composition in CA/MA. Conceptual one-mark items test climacteric behaviour, ethylene, chilling injury, precooling method choice and dryer types.
How our questions for GATE spread across the units of Post-Harvest Engineering of Horticultural Crops. Difficulty: 9 easy, 27 medium, 32 hard.
| Pre-cooling: hydro, forced-air and vacuum cooling | 12 | |
| Dehydration of fruits and vegetables | 11 | |
| Respiration and ripening physiology | 9 | |
| Controlled and modified atmosphere storage | 9 | |
| Juice extraction | 8 | |
| Packhouse design | 5 | |
| Grading, including machine vision | 4 | |
| Value addition | 3 | |
| Processing of spices and plantation crops | 3 | |
| Washing, sorting and waxing | 2 | |
| Minimal processing | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
When malic acid (C4H6O5) is the main respiratory substrate, the respiratory quotient is about
B. 1.33
C4H6O5 + 3 O2 -> 4 CO2 + 3 H2O, so RQ = 4/3 = 1.33. An RQ of 1.0 applies to hexose sugars and about 0.7 to fats, which need more oxygen per carbon. 0.75 inverts the ratio (O2/CO2 = 3/4).
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
A leafy vegetable respires at 60 mg CO2/kg h at 20 degC and its Q10 is 2.5 over 0 to 20 degC. Its respiration rate at 0 degC is about
D. 9.6 mg CO2/kg h
Twenty degrees is two Q10 intervals: R(0) = 60 / 2.5^2 = 60 / 6.25 = 9.6. 12.0 comes from dividing by 2 x 2.5 = 5 instead of 2.5 squared; 24.0 applies only one interval.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
A forced-air cooler must remove 50 kW from produce. The air may warm by 3 K passing through the pallets. Taking air specific heat as 1.005 kJ/kg K and density 1.27 kg/m3, the required airflow is about
D. 13.1 m3/s
Mass flow = 50/(1.005 x 3) = 16.58 kg/s; volume = 16.58/1.27 = 13.1 m3/s. Quoting 16.6 m3/s treats kg/s as m3/s; 21.1 multiplies by density instead of dividing.
Further reading: ASHRAE Handbook — Refrigeration
Compared with room cooling, forced-air cooling of the same packed produce is faster mainly because
C. a pressure difference forces cold air through the carton vents past each item
In room cooling air flows around stacks and heat must conduct out through packages; forced-air cooling pulls air through aligned carton vents so each item is swept by cold air. The air temperature is typically similar in both methods.
Further reading: Thompson et al., Commercial Cooling of Fruits, Vegetables, and Flowers (UC ANR 21567)
Removing field heat from 1 t of produce (specific heat 3.8 kJ/kg K) cooled by 25 K, with a refrigeration system of coefficient of performance 3, requires about how much electrical energy (ignoring fans and losses)?
A. 8.8 kWh
Heat = 1 000 x 3.8 x 25 = 95 000 kJ = 26.4 kWh. Electricity = 26.4/3 = 8.8 kWh. 26.4 kWh is the heat itself; multiplying by COP gives 79 kWh; 31.7 treats MJ as kWh.
Further reading: ASHRAE Handbook — Refrigeration
In chlorinated wash water, the pH is normally held near 6.5 to 7.5 mainly because
C. hypochlorous acid, the most effective form, dominates at slightly acidic to neutral pH
HOCl is a far stronger sanitiser than the hypochlorite ion, which dominates at high pH. Going much below pH 6.5 increases chlorine gas release and corrosion, so a slightly acidic to neutral band is used.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops (UC ANR 3311)
0.5 kg of produce with respiratory quotient 1 consumes 10 mL O2/kg h in a sealed film package of area 0.12 m2. The film's CO2 permeance is 24 000 mL/(m2 day atm) and outside CO2 is negligible. The steady-state CO2 inside is about
C. 4.2%
CO2 output = O2 uptake x RQ = 0.5 x 10 x 24 = 120 mL/day. 120 = 24 000 x 0.12 x p, so p = 120/2 880 = 0.0417 atm = 4.2%. Using the O2 permeance (6 000) instead gives 16.7%. 0.17% omits the x 24 h per day; 8.3% uses only half the film area.
Further reading: Mahajan et al., MAP design literature; Kader
If slice thickness is doubled, other conditions unchanged, the falling-rate drying time to a given moisture ratio (diffusion-controlled) becomes about
B. four times as long
In Fick's solution time appears as D t / L^2, so for the same moisture ratio t is proportional to L^2; doubling thickness quadruples the time.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
Most spoilage bacteria cannot grow in a dried product whose water activity is below about
D. 0.90
Most bacteria need water activity above about 0.90; many yeasts and moulds grow down to about 0.80 to 0.88, and a few xerophilic moulds and osmophilic yeasts to about 0.60. 0.99 is nearly pure water, where almost everything grows, and 0.30 is far below the limit for any microbe.
Further reading: Fellows, Food Processing Technology
A processor blends a 12 degBrix juice with a 65 degBrix concentrate to make 1 000 kg of a 20 degBrix base. The concentrate needed is about
A. 151 kg
Pearson square: juice parts = 65 - 20 = 45, concentrate parts = 20 - 12 = 8; concentrate = 1 000 x 8/53 = 151 kg. Check: 849.1 x 0.12 + 150.9 x 0.65 = 200 kg solids = 20%. 849 kg is the juice, not the concentrate. 178 kg divides the concentrate parts by the juice parts (1 000 x 8/45) instead of the total; 123 kg divides by 65.
Further reading: Fellows, Food Processing Technology
Ten here, 68 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.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
An AI operating system for agriculture: free guides, manuals and tools written for every country.