Storage Engineering Questions and Answers

Answer: C

The insects and the grain between them consume the oxygen and raise the carbon dioxide until the atmosphere becomes lethal. It works only if the seal is genuinely airtight, which is why the technique demands careful construction.

Answer: D

Correct answer: Remove field heat quickly

Precooling removes the field heat that produce carries when harvested - often 25 to 30 degrees - as quickly as possible after picking. Respiration roughly doubles for every ten degree rise, so a few hours at field temperature consumes a disproportionate share of the product's storage life.

Rapid cooling therefore slows respiration, water loss, ripening and microbial growth from the outset. It is not a drying, colouring or densifying operation, and delaying it cannot be made up later: storage life lost in the field is not recovered in the cold store.

Answer: A

Lowering the pressure makes water evaporate from the surface and the latent heat cools the produce in minutes. It works only where the surface area is large enough, which is why lettuce cools well and a potato does not.

Answer: B

Correct answer: Product, respiration and more

A cold store's refrigeration load is the sum of several components. The product load is the heat removed in cooling the produce from its arrival temperature to the storage temperature; the respiration load is the metabolic heat the living produce continues to generate; the transmission load is heat conducted through walls, floor and roof.

To these are added infiltration through doors, and internal loads from lights, fans and people. Sizing on any one component alone would badly undersize the plant - respiration in particular is easy to overlook, yet 40 tonnes respiring at \( 45 \) mW/kg adds \( 1.8 \) kW continuously.

Answer: C

Correct answer: Ethylene accelerates ripening

Ethylene is a plant hormone that triggers and accelerates ripening and senescence, and it acts at concentrations of a few parts per million. Because ripening produce emits it, a store can accumulate enough to ripen its own contents prematurely - and ethylene-producing commodities such as apples and bananas will ripen sensitive ones such as leafy vegetables stored with them.

The remedies are separation of incompatible commodities, ventilation, and scrubbing with permanganate or catalytic oxidisers. Ethylene is not toxic to humans at these levels and does not affect the plant or the humidity.

Answer: D

Correct answer: The atmosphere is set once, then evolves

In modified atmosphere packaging the gas mixture inside the pack is established at sealing and thereafter changes on its own, as the produce respires and gases diffuse through the film. The composition is engineered by choosing the film's permeability so that the evolving equilibrium is favourable.

Controlled atmosphere storage, by contrast, holds the composition actively at a set point with generators, scrubbers and sensors throughout the storage period. Modified atmosphere packaging is used across many commodities, usually still under refrigeration; the distinction is between setting once and controlling continuously.

Answer: A

Correct answer: Insect infestation and mould growth

Insects and moulds together account for the great majority of tropical storage losses, because warm temperatures and high humidity favour both. Insects consume and contaminate the grain and generate heat and moisture that then encourage moulds, which spoil it further and may produce mycotoxins.

Rodents and mechanical damage cause real but smaller losses, and loss of colour is a quality rather than a quantity issue. The dominance of insects and moulds is why the standard measures - drying, cooling, cleaning, sealing and fumigation - are all aimed at those two.

Answer: B

Correct answer: Local materials, passive protection

Traditional structures such as the bukhari and morai are built from locally available materials - mud, bamboo, thatch, timber - and protect the grain passively: raised above the ground against damp and rodents, roofed against rain, and often plastered to limit insect entry.

They need no power, no machinery and no purchased inputs, which is what makes them viable at farm scale. They offer no refrigeration, no controlled atmosphere and generally no fumigation, so their protection is more limited and their losses higher than in an engineered store.

Answer: C

Correct answer: Eliminating gaps they can enter

Rodent proofing is fundamentally a matter of exclusion. A rat can pass through a gap of about 12 mm and a mouse through 6 mm, so every opening - door thresholds, ventilator grilles, service penetrations, junctions between wall and roof - must be closed with material they cannot gnaw, and smooth bands or guards fitted to prevent climbing.

Temperature, fumigation and repellents do not exclude them. Fumigation may kill those already present but leaves the store open to reinfestation the moment ventilation resumes.

Answer: D

Correct answer: Following carbon dioxide evolution

Dry matter loss occurs when grain and the organisms in it respire, oxidising carbohydrate to carbon dioxide and water. Measuring the carbon dioxide evolved therefore measures the dry matter consumed directly, through the stoichiometry of respiration, and it does so early - before any visible spoilage.

Weighing the store cannot separate dry matter loss from changes in moisture content, which are far larger. Bulk density and angle of repose are physical properties affected by many things and give no quantitative measure of loss.