Post-harvest losses (grains) facts for kids
Grains are super important for feeding the world! But sometimes, a lot of grain gets lost before it even reaches our plates. These losses can happen at different times:
- Before harvest: This is when crops are still growing. Pests like insects, weeds, or plant diseases (like rusts) can damage the plants.
- During harvest: This happens while farmers are gathering the crops. Grains can fall off the plants and shatter, meaning they break or scatter.
- After harvest (post-harvest): This is the biggest part! It's all the grain lost from the moment it's harvested until it's eaten. This can happen right on the farm when grains are being separated from their stalks (called threshing) or cleaned (called winnowing) and dried.
Other reasons for losses after harvest include not harvesting at the right time, bad weather, or problems with how the grain is handled and sold. A big problem is often poor storage, which makes grains spoil faster. This is especially true in many developing countries, where farmers store grain for their families or while waiting for better prices.
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Why Do We Lose So Much Grain?
Grains can be lost at almost every step after they are harvested. Let's look at some common ways this happens.
Losing Grain During Processing
When farmers separate grain from the plant, like removing corn kernels from the cob (called shelling), some kernels can be missed or damaged. If machines are used, they might not get all the grain, or they might crack the kernels. Cracked grains are easier for insects to get into.
For crops like paddy, separating the grain from the outer shell (chaff) is called threshing. Grains can spill or not be fully removed. After threshing, if the grain isn't cleaned well, dirt or chaff can stay with it. This can cause problems later when the grain is processed into food.
How Drying Affects Grain Loss
Drying grain is super important to keep it from spoiling. But even drying can cause losses! When grain is dried outdoors, like on roads in some parts of Asia, birds and rodents might eat some of it. Wind from passing cars or nature can also blow grain away. The main problem during drying is when grain kernels crack. This often happens with rice. If grain isn't dried enough, it can spoil completely, making the whole harvest useless. Farmers need to dry their crops well, especially if they plan to store them for a long time. Grain with too much moisture can get moldy, heat up, change color, and spoil. Most grains should be dried within 2-3 days after harvest.
Milling and Storage Losses
Milling is when the outer layers are removed from grain to make it edible, like turning paddy rice into white rice. If the milling machines aren't set correctly, a lot of good grain can be wasted or broken. Even a small improvement in how much whole grain is produced can mean a lot more food for people.
Since grains are harvested only once a year in many places, they need to be stored for a long time – sometimes over a year! This makes storage a very important part of the food supply chain. A lot of grain can be lost during storage, especially corn in Africa.
Losses in stored grain happen because of how the grain, its storage place, and tiny organisms interact.
Mold and Pests in Stored Grain
Molds grow when grain is warm and has enough water and oxygen. The warmer and wetter the grain, the faster mold grows. For example, corn stored at 15°C (59°F) with 15% moisture can last a year. But the same corn at 30°C (86°F) will be badly damaged by molds in just three months.
Insects and mites (tiny spider-like creatures) also cause big problems. They damage the grain and eat its nutrients. They can also carry mold spores, helping mold spread. Insects usually don't infest grain below 17°C (63°F). Mites can infest grain between 3°C and 30°C (37°F and 86°F) if the moisture content is above 12%. When insects and mites are active, they make the grain warmer and wetter, which helps mold grow even more. Broken grain kernels also make it easier for mold to grow.
Rodents like mice and rats are also a big cause of post-harvest losses. Three types of rodents are found all over the world: the house mouse (Mus musculus), the black rat (Rattus rattus), and the brown rat. They eat and contaminate a lot of stored grain.
How Much Grain Is Really Lost?
It's hard to know exactly how much grain is lost, but it's a lot! In some developing countries, especially for small farms, up to 40% of grain can be lost. In Africa, about 10-20% of corn is lost from harvest to market. About 40% of these losses happen during storage on the farm, 30% during processing (like drying and threshing), 20% during transport from the field, and 10% during transport to the market.
Trying to Reduce Grain Loss
Many groups, including governments and aid agencies, have tried to help farmers reduce post-harvest losses. But it's still a big challenge. One problem is that new technologies for drying and storage, even if they work well, are often not used by small farmers. This might be because the farmers aren't sure the new methods will help them enough, or the cost is too high.
Sometimes, farmers don't get paid more for selling better-quality, drier grain. So, even if they improve their drying, it doesn't help them earn more money. This means that focusing only on new machines or technologies isn't enough. We also need to think about what farmers need and how the market works.
For example, some expensive driers made of local wood were eaten by termites. Others made of sawn wood were too costly. In the 1980s, there was excitement about strong storage bins made of cement or brick, but farmers often found them too hard or expensive to build.
Success Stories in Reducing Loss
There have been some good ideas that worked! In the Central African Republic, a simple 1-tonne storage structure was easy for farmers to build and became popular. Metal bins have also been very successful in Central America and Eswatini for many years. However, spreading these successes to other areas can be tricky if there aren't local craftspeople to build them or if the grain needs special drying or treatment.
Smaller bins used inside homes seem to work better than larger outdoor bins. A newer idea is using special sealed bags called "hermetic bags." These bags keep air and moisture out, which helps store grain without chemicals. The Purdue Improved Cowpea Storage (PICS) bags are an example, used for storing cowpeas. Similarly, the GrainPro SuperGrainbag is another type of hermetic bag that helps store rice and other grains very well. These bags offer good ways to store different amounts of grain safely.
