Rice and corn: Harvest and storage
Let’s move on to see how rice and corn are harvested and stored.
Rice grows in ears, in envelopes called glumes.
Once rice has been harvested, it needs to be threshed to separate the glumes from the ear of rice. This process can be carried out either manually, or with the help of animals, or by using machines. This step releases what is referred to as paddy rice. The husk covering paddy rice is hard and inedible. Once it has been removed, we get what is called wholegrain rice, brown rice or cargo rice, which has many nutritional properties.
Removing the germ and the bran (another envelope that covers the grain) gives white rice. The grains are then parboiled.
What about corn? It can be harvested either in cobs or as kernels, but it is now more commonly harvested as kernels. This entails a process called shucking, to separate the kernels from the cobs. The corn is then hulled to remove part of the germ and the bran.
Corn can also be consumed in its original state, i.e. without having undergone any transformations.
After harvesting and threshing, grains of rice and kernels of corn usually still have a high water content, which promotes the growth of mould and bacteria. So, they must be dried. This step is also called desiccation..
There are two main methods for drying rice: natural drying and artificial drying.
Natural drying consists essentially of exposing the grains of rice to air, sun or shade. This method is suitable for small quantities of rice, but may be limited by the climate. Natural drying is not recommended in humid regions or during the rainy season. Moreover, if drying is insufficient or too slow, it can cause significant losses.
The technique for drying rice artificially was developed in order to dry the grains faster, in greater quantities, and without relying on the climatic conditions. However, this method requires the purchase of dryers and the use of fuel so it is more complex than natural drying and more costly in terms of energy.
There are also several methods for drying corn: natural drying on the stalk, drying on the cob and drying kernels.
Natural drying on the stalk means that, before harvesting, corn is left to dry for several weeks after it has reached maturity but whilst still on its stem. This simple method has major disadvantages: The corn remains in the field, delaying the preparation of the soil for another crop, and rodents, birds and insects may attack the cobs.
Drying corn whilst still on the cob, but after harvesting, avoids these disadvantages. The cobs are hung in an area where air circulates freely. Natural ventilation is often inadequate, especially in humid regions so, in many cases, artificial ventilation is required.
Drying kernels of corn is carried out after shucking. Since kernels of corn are very moist, they deteriorate very quickly, so artificial dryers are often used to speed up the process. This method makes it possible to dry large quantities of corn in a relatively short period of time.
After rice and corn have been dried, they are then stored.
The main objectives of storage are to allow the deferred use of agricultural products and to guarantee a regular and continuous supply for processing industries. Storage also serves to balance the supply and demand of agricultural products on a commercial basis, thereby stabilising market prices.
Most of the time, rice and corn are stored in bags for transportation and sale.
However, in large collection centres, ports or large processing sites, rice and corn are stored in bulk in warehouses or in silos. Such large facilities can hold up to 15 000 cubic metres, equivalent to five Olympic swimming pools. They require ventilation to maintain a suitable temperature and especially a low level of humidity. This can represent a significant energy cost, as storage of 15 000 tonnes of rice or corn in silos consumes about 160 000 kilowatts per year.