Storing grains and fresh produce at home

24 min

Let's begin

After the maize harvest, many families in Rwanda hang the cobs in rows under the eaves of the house, as in the first photo below. The sun and the wind dry them, the roof keeps off the rain, and the height keeps them away from goats and chickens. It is a good start. But the next steps decide whether the grain feeds the family until the next harvest or is eaten by weevils and rats, or turns mouldy and poisonous. Storing food at home, with no cold room or freezer, depends on three things: making the food dry and clean, choosing the right container, and checking it often.

Definition

Post-harvest loss: food lost between harvest and eating, through pests, mould, damage, rotting or waste.

Moisture content: the percentage of a grain's mass that is water. Maize is safe to store for months when it is below about 13%.

Aflatoxins: poisons made by some moulds (Aspergillus) that grow on damp maize, groundnuts and other foods. They cannot be seen, smelt or destroyed by ordinary cooking.

Hermetic storage: storage in an airtight container, such as a triple-layer bag or a sealed drum, in which insects use up the oxygen and die.

Storing grains and pulses: four steps

Dry. Dry the grain on a tarpaulin or mat in the sun, never on bare ground, where it picks up damp and soil moulds. Turn it often and cover it at night and in rain. Dry grain is hard, and rattles when shaken.
Clean and sort. Winnow off chaff and dust; pick out broken, mouldy, discoloured and insect-damaged grains. One mouldy cob can spoil a whole bag.
Choose the container (table below), and place it on a raised platform or pallet, off the floor and away from the walls, in a dry, rat-proof place.
Check monthly for insects, warmth, damp, smell and droppings, and use the oldest grain first.

Store	Advantages	Disadvantages
Traditional granary (ikigega): woven, raised on legs, thatched	made from local materials; airy, so grain stays dry; raised away from damp	insects and rats can get in; must be repaired often
Woven polypropylene sacks	cheap; easy to move and stack	insects pass straight through; need pallets; rats chew them
Hermetic (triple-layer) bags	kill insects without chemicals; protect dry grain for months	must be sealed carefully; grain must be dry; a hole ruins the seal
Metal silos and sealed plastic drums	airtight; rat-proof; last for years	costly; can sweat if left in the sun

Purdue Agriculture: the PICS (Purdue Improved Crop Storage) bag. Watch how each of the two inner liners is twisted and tied separately before the outer bag is closed, and why no insecticide is needed.

Fresh produce at home

Food	How to store it	Why
Irish potatoes	dark, cool, airy place, in a basket or sack; not with onions	light turns them green and bitter; onions make them sprout
Sweet potatoes, pumpkins	cool, dry room, not in the fridge; handle gently	bruises rot; cold damages them
Cooking bananas and ripe bananas	hang the bunch in a cool, shaded place	air around them slows rotting; cold blackens them
Tomatoes, avocados	room temperature until ripe, then use or refrigerate	they ripen best in warmth
Leafy vegetables (amaranth, cassava leaves)	wrap in a clean damp cloth in a cool place; use within 1 to 2 days	they wilt and lose vitamins fast
Fresh milk with no fridge	boil it, cool it fast, keep it covered in the coolest place; use it within the day	boiling kills germs, but bacteria grow again in warm milk

Worked example

Worked example 1: is a hermetic bag worth it? Illustrative figures. A family stores 300 kg of dry maize for six months. In ordinary sacks they expect to lose 15% to insects; in hermetic bags, 1%. Maize is worth 400 Frw per kg, and three 100 kg hermetic bags cost 3,600 Frw in total. Compare.

Loss in sacks: $300 \times 0.15 = 45$ kg. Loss in hermetic bags: $300 \times 0.01 = 3$ kg.
Maize saved: $45 - 3 = 42$ kg, worth $42 \times 400 = 16{,}800$ Frw.
Net gain: $16,800 - 3,600 = 13,200$ Frw in the first season, more if the bags are reused.

Worked example

Worked example 2: the salt test. How can a farmer without a moisture meter check whether shelled maize is still too wet?

Dry some ordinary salt in a pan and let it cool.
Fill a clean, dry glass jar about one-third with maize, add two or three spoons of the salt, close the lid and shake for 2 to 3 minutes; leave for 15 minutes.
If salt sticks to the inside of the jar, the maize is too wet (above about 15% moisture): dry it longer.
If the salt stays loose, the maize is drier than about 15%. For long storage it should be drier still, below about 13%, so keep drying for another sunny day or two.

Warning

Aflatoxins. Never eat, sell or feed to animals grain or groundnuts that are mouldy, discoloured or smell musty. Aflatoxins are not destroyed by ordinary cooking; a large dose can kill, and long-term eating of small amounts damages the liver and can cause liver cancer. Only use storage insecticides that are approved for food grain, at the dose on the label, and never use crop sprays or other chemicals on stored food.

Tip

Memory hook: "Dry, Clean, Seal, Raise, Check." Most grain losses at home come from skipping one of these five words.

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Practice

Define post-harvest loss and give three causes.
Why is grain dried on a tarpaulin and not on bare ground?
Explain how a hermetic bag kills insects without chemicals.
Give one advantage and one disadvantage of a traditional granary.
Why should Irish potatoes not be stored in the light or next to onions?
Illustrative: 500 kg of beans are stored. Losses are 12% in ordinary sacks and 2% in hermetic bags. How many kilograms are saved by using hermetic bags?
A trader buys cheap, slightly mouldy maize, mixes it with good maize and sells the mixture as animal feed. Evaluate this practice.

Show answersHide answers

Food lost between harvest and eating. Causes: insects, rodents, mould, moisture, physical damage, poor handling and rotting (any three).
Bare ground passes damp and soil moulds to the grain and adds dirt and stones; a tarpaulin keeps it clean and lets it dry evenly.
The bag is airtight. Insects and the grain use up the oxygen inside and give off carbon dioxide; without oxygen the insects stop feeding and die.
Advantage: made from local materials, airy and raised, so grain stays dry. Disadvantage: insects and rats can get in; it needs frequent repair.
Light turns potatoes green and bitter (the green parts contain a harmful substance); onions give off gases and moisture that make potatoes sprout and rot.
$500 \times (0.12 - 0.02) = 500 \times 0.10 = 50$ kg.
It is unsafe and dishonest. Mould can produce aflatoxins that harm animals and pass into milk and eggs, and mixing spreads the poison through the good maize. Mouldy grain should be removed and destroyed, not sold.

1Storing grains and pulses: four steps

2Fresh produce at home

Storing grains and pulses: four steps

Fresh produce at home