Storage Engineering Questions and Answers

Answer: C

Correct answer: Only three

Three pairs are right. Higher moisture content shortens storage life by permitting mould growth; higher temperature shortens it by accelerating respiration, mould and insect development; and damaged or broken grain shortens it by exposing the starchy endosperm to moulds and insects and by holding more moisture.

The fourth is wrong and inverts the effect. Cleaning before storage lengthens storage life: removing fines, trash and damaged kernels takes out the material that carries most of the moisture, spores and insect eggs, and improves airflow through the bulk as well.

Answer: D

Correct answer: Only three

Three pairs are right. Temperature probes in the bulk detect developing hot spots, which is their purpose; carbon dioxide measurement detects respiration and hence early spoilage, often before temperature responds; and moisture meters on samples reveal moisture migration and wet pockets.

The fourth is wrong. Bulk density is affected by variety, moisture, cleanliness and packing, so it is far too insensitive and ambiguous to detect infestation. Insects are found instead by sieving samples, by probe or pitfall traps, or by acoustic and carbon dioxide monitoring.

Answer: A

Correct answer: Precooling of perishables

Precooling is a measure for harvested perishables - removing field heat to slow respiration and senescence. It concerns fruit and vegetables rather than stored grain, and insects are not what it targets.

The other three are all insect control measures for stored grain. Fumigation with phosphine kills the infestation chemically; controlled atmosphere storage kills it by depriving it of oxygen or exposing it to high carbon dioxide; and aeration to cool the bulk suppresses breeding by taking the temperature below about 15 degrees.

Answer: B

Correct answer: Cleaning to remove fines and damaged grain

Cleaning lengthens storage life. Fines, trash and broken kernels carry a disproportionate share of the moisture, mould spores and insect eggs entering the store, and they also block the interstitial spaces so that aeration air cannot move freely. Removing them addresses several problems at once.

The other three all shorten storage life: a higher temperature accelerates respiration, mould and insect development; a higher moisture content permits mould growth; and broken kernels expose the endosperm and hold moisture, which is exactly what cleaning removes.

Answer: C

Correct answer: Compressor motor heat rejected outdoors

Heat rejected outdoors at the condenser is not a load on the cold room. It is heat the plant has already removed, together with the work done in removing it, discharged to ambient outside the insulated envelope - so it never enters the space being cooled. A compressor located inside the room would be a different matter.

The other three are genuine loads: the product cooling load from bringing produce down from its arrival temperature, the respiration heat the living produce generates continuously, and infiltration of warm moist air through door openings.

Answer: D

Correct answer: Crusting and mould on the top surface

Crusting and mould on the top surface is a failure, and a diagnostic one: it is the signature of moisture migration. Convection currents in the interstitial air carry moisture from the warmer core to the cold underside of the roof, where it condenses and wets the surface layer, and moulds establish there even though the bulk average moisture is unchanged.

The other three describe good management. An even temperature means the gradients driving migration have been removed, the correct safe moisture prevents mould growth, and carbon dioxide monitoring catches spoilage before it is visible.

Answer: A

Correct answer: Controlled atmosphere store

A controlled atmosphere store is the opposite of low-cost: it needs a gas-tight envelope, generators and scrubbers to establish and hold the atmosphere, instrumentation to monitor it, and continuous energy - justified only by high-value commodities.

The other three are traditional or low-cost structures built from local materials with no purchased inputs. The bukhari and morai are raised, plastered or thatched farm granaries of the Indian subcontinent, and underground pits exploit stable soil temperature and, when well sealed, a naturally hermetic atmosphere.

Answer: B

Correct answer: Moisture has migrated upward

The pattern is the classic moisture migration failure. In a cold winter the silo wall and roof cool while the core of the bulk stays warm, and the resulting temperature difference drives a slow convection current: air warmed at the centre rises, carrying moisture, and on reaching the cold roof is cooled below its dew point and deposits it on the surface grain.

That wetted layer supports mould growth and cakes into a crust, even though the grain was sound and dry when stored - the average moisture is unchanged, only redistributed. Aeration prevents it by removing the gradient that drives the circulation.

Answer: C

Correct answer: A hot spot is forming

Rising carbon dioxide with normal probe readings is the expected early signature of a developing hot spot. Respiration releases carbon dioxide that diffuses through the whole bulk and reaches any sampling point, whereas the heat it also generates stays local, because grain conducts poorly and the interstitial air moves slowly.

A probe therefore responds only if it happens to be within or very near the developing spot. The carbon dioxide reading is the more sensitive instrument, and a steady rise warrants investigation - probing, sampling and aeration - rather than reassurance.

Answer: D

Correct answer: The structure leaked

A leaky structure is the standard explanation for both outcomes at once. Phosphine acts slowly and must be held at a lethal concentration for the full exposure period - several days - to reach eggs and pupae as well as adults. If the gas escapes, the concentration falls below lethal while some individuals are still alive.

Those survivors are disproportionately the least susceptible, so repeated sublethal exposures actively select for resistance. This is why sealing quality, not dose, is usually the critical variable, and why raising the dose in a leaky store makes the resistance problem worse rather than better.