Guidelines for Storing Grains in Plastic Bags

This is a low-cost technology, but various points must be kept in mind in order to avoid losses during the storage of the grains: 

1. The basic principle is to keep the grains dry in a modified atmosphere, with low oxygen content and a high concentration of carbon dioxide (CO₂). This gives control of insects and fungi that are the major causes of increases in the temperature of the grains. 

2. It should also be considered that grains are living organisms and must be healthy, clean and without mechanical damage in order to have a greater chance of maintaining their quality during storage.  

3. The place where the bag is laid must be as high as possible, far from trees and from any possible source of breakages. The ground must be firm and plain, to enable the bag to be laid properly without its bottom part breaking. This also helps when emptying it. It must be laid in a north – south direction.  

4. The suitable make-up of the bag depends on many factors, one of which is the quality of the bagging machine. With a well-built and well-designed machine, it is easier to obtain well-made-up bags. 

5. The principle for making up the bag, so that it stretches appropriately, is based on maintaining a dynamic and steady rhythm while filling it. This is done by regulating the braking, which depends on the brake of the machine itself and on good preparation of the land. 

6. Bag quality is fundamental for good conservation. The bag must permit sufficient stretching over a prolonged period of time, without losing its grain-holding capacities and its impermeability. 

7. It should be noted that the pressure when filling is mainly produced by the specific weight of each particular grain, and to a lesser extent by the auger of the bagger. As the grain pours in, it gradually pushes the cereal lightly against the bag-filling wall. The bag in turn exerts resistance to the stretching that is regulated mainly with the bagger brake.  

8. All these factors must come together for the bag to be made up with a diameter that is even and with uniform stretching. This requires the bag to be filled well enough to expel the greatest possible quantity of air, neither leaving the bag "loose", nor surpassing the stretching capacity recommended by the manufacturers. This is measured by the rule found on the side of the bag.   

9. The most important aspect to bear in mind is the augers, both of the bagger and of the extractors. The augers should be of the greatest diameter possible, well-centred in the tube, well-finished, with low revolutions and working with the least possible slope. They must also be operated completely full. When the augers are worn, it is better to avoid using the machine, since this causes significant mechanical damage to the grains. The augers should be changed, for a new one, once they are worn-out.  

10. As a general rule, the humidity with which the grains should be stored must not be greater than the base humidity for commercialization. The lower the humidity of the grain, the better it will keep and the more time it will be possible to keep it. In the case of seeds, the conditions are even stricter.  

11. As the humidity of the grain to be bagged increases, so too does the risk of damage. Tests made by INTA have shown that the quality of grains tends to deteriorate when they are stored in silo bags for a long period of time and with high humidity content. Damp grains can only be stored in plastic bags when it is an emergency and there is no other alternative. In these cases it is advisable to mount, 40 cm above the bag, a cover with a plastic net (80% of shadow) when the spring comes. It will attenuate the incidence of the outside temperature and reduce the risk of grain damage. 

12. It should be remembered that this is a simple technology, but that it needs extreme care to protect and maintain the integrity of the bag. There must be permanent monitoring so that any breakages are immediately repaired.  

13. Lastly, particular care must be taken after emptying the bag to pick up all the remains of plastic. Plastic remains are one of the most dangerous contaminants of the environment. The farmer is recommended to collect every kind of plastic (used bags and containers from pesticides) and keep them in one place to be sold later. Every measure should be taken to ensure they do not scatter around the environment.  

14. When planning storage in plastic bags, it is recommended to keep in mind the following guidelines:

Guidelines for Storing Dry Grains in Plastic Bags

It is not recommended to store wheat with a humidity above  14% for a long period (greater than 90 days)

The risk is measured taking into consideration the humidity of the grain, the normal aging of the bag and the possibility of the bag being broken by external agents. It As the ambient temperature increases, the risks increase When the grains are damaged, the risks increase When the grains are dirty (impurities), the risks increaseimportant to bear in mind that these risk values are guidelines, are not absolute and that they may vary in different situations.

With these guidelines the farmer can plan the storage and the monitoring that must be carried out so as not to lose quantity and quality in the grains being kept. That is, for example, that the bags containing grains that are damper, and/or damaged, and/or with impurities, will be the ones that must be taken care of most intensively. These must be the first ones to be delivered for commercialisation, and the others that contain dry, healthy and clean grains left for the end.

This is a simple technology but it needs maximum care: in the quality of the grain to be stored, in the quality of the bag, in its filling and in its subsequent monitoring.

Information prepared by: Cristiano Casini, Ph.D. (ccassini@correo.inta.gov.ar )
INTA EEA Manfredi – January 2005