ICAR AIEEA-PG / PGS — Code 18 Food Science Technology · India · ICAR through the National Testing Agency
Original practice questions written to the published syllabus · not past papersRemoving water from liquid and solid foods: evaporator types and energy economy, drying theory and dryer design, spray, drum and freeze drying, concentration by freezing and membranes, and the quality changes that drying causes. Agricultural Engineering's post-harvest-cereals-pulses-oilseeds covers grain drying; this subject covers processed foods and powders.
In the exams: GATE XE-G Section 4 (evaporation, hot-air drying, spray and freeze drying, psychrometry); ICAR AIEEA-PG Code 18 Units II–III
ICAR AIEEA-PG / PGS — Code 18 Food Science Technology
Unit II lists evaporation and drying among unit operations and equipment, and Unit III lists dehydration and concentration methods. MCQs test definitions and comparisons: types of evaporators and dryers, concurrent versus countercurrent tunnels, drum versus spray drying, freeze-drying principles, IMF water activity range, and simple balances.
How our questions for ICAR AIEEA-PG / PGS spread across the units of Evaporation, Dehydration & Concentration of Foods. Difficulty: 18 easy, 35 medium, 1 hard.
| Psychrometry, humidification and dehumidification | 7 | |
| Quality changes in dried foods and rehydration | 6 | |
| Drying theory: constant-rate and falling-rate periods | 5 | |
| Hot-air dryers: cabinet, tunnel, belt and fluidised-bed | 5 | |
| Spray drying: atomisation, powder properties and agglomeration | 5 | |
| Evaporation: boiling-point elevation and heat transfer | 4 | |
| Single- and multiple-effect evaporators; steam economy | 4 | |
| Falling-film, forced-circulation and plate evaporators | 4 | |
| Freeze drying: principles, cycle design and collapse temperature | 4 | |
| Osmotic dehydration and intermediate-moisture foods | 4 | |
| Drum drying | 3 | |
| Freeze concentration and membrane concentration | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
As air passes over wet food in an adiabatic dryer, its state follows approximately a line of constant
A. wet-bulb temperature
Heat for evaporation comes from the air's sensible heat, so the air cools and gains moisture along a near-constant wet-bulb (and enthalpy) line. Dry-bulb and W both change; RH rises.
Further reading: Singh and Heldman, Introduction to Food Engineering
The dew point of a sample of air is the temperature at which
A. the air becomes saturated when cooled at constant humidity ratio
Cooling at constant W raises RH until it reaches 100 % at the dew point; further cooling condenses water. The wetted-bulb reading is the wet-bulb temperature.
Further reading: Singh and Heldman, Introduction to Food Engineering
Air at 30 °C has a water vapour partial pressure of 2.0 kPa; the saturation vapour pressure at 30 °C is 4.246 kPa. Its relative humidity is closest to
B. 47 %
RH = pv/ps = 2.0/4.246 = 47 %. 212 % inverts the ratio and exceeds 100 %; 1.3 % is the humidity ratio expressed as a percentage; 2.0 % confuses kPa with per cent.
Further reading: Singh and Heldman, Introduction to Food Engineering
10,000 kg/h of juice at 12 % solids is concentrated to 48 % solids. The water evaporated is
B. 7,500 kg/h
V = F(1 − xF/xP) = 10,000 × (1 − 12/48) = 7,500 kg/h. 2,500 kg/h is the concentrate; 3,600 kg/h multiplies the feed by the difference in percentages (10,000 × 0.36); 9,750 kg/h treats 12/48 as 2.5 %.
Further reading: Singh and Heldman, Introduction to Food Engineering
The evaporator type most widely used for concentrating milk and fruit juices is the
B. falling-film evaporator
Falling-film units give short residence times at low ΔT and suit multiple effects and MVR. Open pans and short-tube units give long residence times; agitated thin-film units are for very viscous products.
Further reading: Fellows, Food Processing Technology
A vegetable contains 80 % moisture on a wet basis. Its moisture content on a dry basis is
D. 4.0 kg water/kg dry solids
X = 0.80/0.20 = 4.0. 0.80 repeats the wet basis; 0.25 inverts the ratio; 1.25 is 1/0.80.
Further reading: Singh and Heldman, Introduction to Food Engineering
During the constant-rate period of drying, the surface temperature of the product is close to
A. the wet-bulb temperature of the drying air
With free water at the surface, heat input balances evaporation and the surface stays near the wet-bulb temperature, which is why hot air does little damage early in drying.
Further reading: Singh and Heldman, Introduction to Food Engineering
Two-stage spray drying with an integrated fluidised bed saves energy because
D. the bed finishes the last drying gently at lower temperature
Removing the last water slowly in a fluid bed at moderate temperature is more efficient and gentler than doing it all in the main chamber.
Further reading: Fellows, Food Processing Technology
Intermediate-moisture foods typically have a water activity of about
C. 0.6 to 0.9
IMFs are soft but shelf-stable, commonly aw 0.6–0.9 with 15–50 % moisture. Below 0.6 foods are dry; above 0.9 most bacteria grow.
Further reading: Fellows, Food Processing Technology
Sulphur dioxide or sulphites are traditionally used on dried apricots mainly to
D. prevent browning and help retain colour and vitamin C
Sulphites inhibit enzymatic and non-enzymatic browning and protect ascorbic acid; their use is permitted and labelled in many but not all markets.
Further reading: Fellows, Food Processing Technology
Ten here, 54 in the app. The Laisha app has every practice question we have written to ICAR AIEEA-PG / PGS 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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