IMPORTANCE OF MOISTURE AND TEMPERATURE IN SAFE STORAGE

OF FOOD GRAINS

Factors affecting quality of grains during storagePhysical factors

TemperatureMoisture & relative humidity

Chemical factorsBiochemical deteriorationPesticides

Biological factorsInsects and mitesRatsBirdsMicro-organisms

Engineering factorsStructural Factors

Bag storage Bulk storage

Handling equipments

Abiotic variablesMoistureTemperature

Biotic variablesMicroorganismsInsectsMitesProperties of the grains

Scientifically visualized controls bring ideal balance in the relationship of the abiotic variables with the biotic variables, which ensure proper grain preservation and soundness. When these relationships got disturbed due to unfavourable storage conditions or defective practices, spoilage occurs.

So the scientific storage of food grains in India is of para mount importance

The effects of temperature and moisture content in safe storage of food grains are inter related

Grains are living beings and respireDuring respiration oxygen is taken up and and inherent carbohydrates are catabolised to CO2 and water. In the process heat is also produced.This decomposition causes a material loss of weight, commonly known as dry matter loss.

Respiration activity is mainly influenced by – Temperature and moisture content

Upto moisture content of 15% , this activity is extremely lowFurther 2% rise from 15% to 17% will increase the CO2 production by 80 times.

Grains have low thermal conductivityThe heat produced during respiration is accumulated and grain temperature rises.

The grain being hygroscopic in nature picks up and gives up moisture from atmosphere and attains equilibrium.

Moisture content (%) g dry matter Loss (%)

11.0 0.21 0.000214.5 0.96 0.00117.0 83.90 0.0820.5 244.8 0.2433.0 1364.00 1.36

Loss of dry matter through respiration of 100kg wheat at 180C within 10 days

Temperature 0C g dry matter Loss (%)

18.0 0.96 0.00130 5.1 0.00540 13.6 0.01352 169.8 0.017

Loss of dry matter through respiration of 100kg wheat at 14.5% within 10 days

Mean values of dry matter loss for a storage period of six months15.0% moisture, at 200C = 0.38% dry matter loss 15.0% moisture, at 60C = 0.38% dry matter loss

Sr. No. Stored cereal Safe moisture content (WB, %)

1 Wheat 12.0

2 Paddy 14.0

3 Rice 13.0

4 Corn 13.0

5 Soybean 12.0

Critical moisture content(%) for safe storage of cereal grains

Harvesting and drying• Grain moisture

content (12-14%)• Minimize cracked and

broken grain during processing

• Don’t mix old and new grain

MoistureMigration

ResultsFrom

Non-uniformTemperature

Hot spot caused by insects

Hot spot spreading

From warm moist air

Condensation near cool surface

Damage due to moisture rising from hot spot

mould

Sprouting of grains

Spoilage of grains due to development of insect and fungi

Outside air temperature above grain temperature

Damage at bottom

Outside air temperature below grain temperature

Damage at top

Management for successful storage:

Control of temperature

Control of seed moisture

Control of temperature Temperature is one of the most important environmental factors which influence seed viability and vigour during storage, the lower the temperature; the longer the seeds maintain germination capacity. Thus, temperature control is an important consideration in building seed storage. Temperature control may be achieved in one of the following ways: Ventilation Insulation Refrigeration

These methods are not mutually exclusive, and are normally used to supplement each other. Ventilation Ventilation could be used to reduce seed temperature and seed moisture content, if used judiciously. In addition, it also helps prevent hot spots from developing; the formation of convection air currents and maintenance of uniform seed moisture content and temperature. Time of ventilation: Whenever the outside temperature of air and relative humidity are low enough to benefit the seeds, either by reducing seed temperature or seed moisture content, the ventilating fans (exhaust fans) can be turned on.

Advantages of Silo Storage• Space required in Silo facility is 1/3rd against

conventional storage• Quick transaction of farmer’s produce in most efficient

& transparent manner• Lesser threat from weather & hence lesser possibility of

grain spoilage• Efficient clearing of mandis during season & usage of

silos as storage point after the procurement season is over

• Economical linkages to Rail heads• No glut in mandis• Elimination of unproductive operations & reduced

losses

Contd…

• Scarcity of labour & inefficient labour operations further justify need for silos

• Right from farm till its sale in mandi, foodgrains are handled in bulk. Hence Silo Storage is best match for mechanical bulk handling in mandis

• Some existing storage facilities in Punjab/ Haryana are far from procurement as well as Rail heads resulting in excessive transportation cost.

Contd…..• 90% of wheat arrives in Punjab/ Haryana Mandis in

just 20 days resulting in choking of mandis• Increasing arrivals require expansion & upgradation of

Mandis• Horizontal expansion needs heavy investments in land• Many mandis are situated in commercial areas, where

further expansion may not be feasible. Alternately, these can be profitably used for other commercial ventures

• Booming economy & more employment opportunities in labor surplus states like Bihar, UP, Orissa has created labor shortage in Punjab/ Haryana

Contd…• Inefficient manual operations carried out in

mandis at present cannot cope up with peak marketing requirements of state

• Limited resources of transporters result in non lifting of stocks on day to day basis causing choking of mandis during peak season

• Unpredictable weather during season threatens procurement process besides spoiling the stocks lying in open yard

• Present manual operation creates lot of environmental problems

• Weighment & Quality Check System in present mandis is not effectively implemented due to inherent limitations of the manual system

The following table shows the EMC of paddy under different storage conditions. The green colored areas represent the desirable environmental conditions for safe storage of paddy or rough rice in the tropics. The yellow areas represent conditions for safe seed storage. Grain needs to be stored at less than 14% moisture and seed at less than 12%. 

At the time of storage

Initial wt of wheat = 100 kgIMC = 12%Wt of dry matter (BDW) = 88 kg

At the time of dispatch

Moisture content = 13%Final wt of wheat = W

100*WBDWW

MC

W= 101.149 kg

At the time of dispatch

Moisture content = 11%Final wt of wheat = W

W= 98.876 kg