Storage Engineering Questions and Answers

Answer: C

Correct answer: It is the same for all commodities

This is the false statement. Safe storage moisture varies widely by commodity - about 14 per cent for paddy, 13.5 for wheat and maize, but only about 7 per cent for groundnut kernel.

The other three are true. It is lower for oilseeds, because oil holds no water and so the same equilibrium relative humidity is reached at a lower stated moisture; it interacts with temperature in setting storage life, the two compounding one another; and it is derived from the equilibrium relative humidity at which moulds grow, about 70 per cent, which is the constant across commodities.

Answer: D

Correct answer: Raising the storage temperature

Raising the storage temperature shortens storage life rather than extending it. Respiration, mould growth and insect development all accelerate with temperature - insects breed fastest between 25 and 33 degrees, and safe storage life for wheat at 13 per cent falls from 1200 days at 10 degrees to 180 at 30.

The other three all extend it: a lower moisture content puts the equilibrium relative humidity below the mould threshold, cleaning removes the fines that spoil first and block airflow, and aerating to cool the bulk slows every deteriorative process at once.

Answer: A

Correct answer: Heat rejected outside at the condenser

Condenser heat is rejected outside the insulated envelope, so it is not a load on the cold room at all. It represents heat the plant has already removed together with the work of removing it, and its disposal is a matter for the condenser's siting and airflow, not for the room's load calculation.

The other three are all components: respiration of the produce, transmission through the insulation, and infiltration through door openings. To these are added internal loads from lights, fans and people working in the space.

Answer: B

Correct answer: Misguided: ventilation restores the oxygen

The proposal would defeat the storage method. Hermetic storage works because respiration inside a sealed structure depletes the oxygen and raises the carbon dioxide until the atmosphere kills the insects; weekly ventilation would restore the oxygen each time and reset the process before it could take effect.

Nor would the grain be kept fresher - the low-oxygen atmosphere is itself what preserves it, and admitting fresh air also admits moisture. Condensation is managed by storing grain dry and by the structure's insulation, not by breaking the seal.

Answer: C

Correct answer: It carries moisture to the cold surface

Moisture migration moves moisture from the warmer part of a bulk to the coldest surface it reaches. Convection currents in the interstitial air pick up moisture where the grain is warm, and deposit it where the air is cooled below its dew point - usually the underside of the roof and the surface grain beneath it.

It therefore wets the top of the bulk rather than drying it, which is why crusting and mould appear there. Sealing does not prevent it, since the driving force is internal, and it occurs whenever a temperature gradient exists - commonly in cold weather, when the bulk is warmer than its surroundings.

Answer: D

Correct answer: Raising the bulk temperature to 30 degrees

Thirty degrees is close to the optimum for most storage insects, whose generation time there is under a month. Raising the bulk to that temperature would accelerate the infestation, not reduce it.

The other three all reduce insect losses. Cooling below 15 degrees arrests development entirely; fumigating a well-sealed structure kills the population outright, provided the concentration is held for the full exposure; and a controlled atmosphere of high carbon dioxide or low oxygen kills them without chemicals.

Answer: A

Correct answer: It reduces the moisture content of the produce

This is the false statement. Precooling removes heat, not moisture, and indeed a well-run precooling operation is designed to minimise water loss - hydrocooling and icing add water rather than removing it, and forced-air cooling is run at high humidity to limit wilting.

The other three are true. It removes field heat quickly after harvest; it slows respiration and senescence, which is why it extends storage life; and vacuum cooling suits produce with a large surface-to-volume ratio, such as leafy vegetables, because it works by evaporating water from the surface.

Answer: B

Correct answer: Bulk density measurement

Bulk density is affected by variety, moisture content, cleanliness, kernel size and how the bulk was filled, so a change in it is ambiguous and a small early change is undetectable. It gives no useful warning of incipient spoilage.

The other three are all standard monitoring tools. Carbon dioxide monitoring is the most sensitive, responding wherever the sample is drawn; temperature probes detect hot spots once heat has accumulated locally; and moisture testing of samples reveals migration and wet pockets before mould becomes visible.

Answer: C

Correct answer: High carbon dioxide or low oxygen kills insects

Controlled atmosphere storage works by altering the gas composition - raising carbon dioxide, lowering oxygen, or both. Insects at every life stage depend on aerobic respiration, so such an atmosphere kills them over days to weeks and leaves no chemical residue.

It has nothing to do with drying the grain. It requires a well-sealed structure to hold the atmosphere, and generators, scrubbers and instrumentation to establish and maintain it - which makes it among the more expensive methods, not the cheapest.

Answer: D

Correct answer: Fines spoil first and impede airflow

Fines, dust, weed seeds and broken kernels are the most vulnerable material in the store: damaged and metabolically active, they carry a disproportionate share of the moisture, mould spores and insect eggs, and they spoil first, seeding trouble in the sound grain around them. They also pack into the spaces between whole kernels, raising the resistance to airflow and creating pockets aeration cannot reach.

Cleaning does not itself lower the moisture content of the sound grain, nor does it kill insects, and any change in bulk density is incidental.