STORING THE GRAIN

Grain is harvested only once a year and needs to be stored for 12 months to ensure that flour and therefore bread, biscuits, and a huge variety of other foods are available all year round. Grain is also used for animal feed. As well as housing the grain until it is moved on to the miller or other processors, storage can even out fluctuations in market supply, either from one season to the next, or from year to year.

Keeping the grain in good condition – the storage process

Because it is stored for such a long period of time, care needs to be taken to avoid the grain becoming mouldy or being infested by insects. The following procedures ensure that even after 12 months or more in store, grain is still of good quality.

Store preparation

• Stores must be clean, dry and well ventilated. Equipment must work properly. Preparation should include ensuring adequate facilities to segregate varieties and to ensure proofing structures against rodents.

Drying and cooling

• Temperature and moisture interact to provide suitable conditions for fungi and mice and therefore moisture management is vital.
• Grain must be 'conditioned' before it is stored. That means dried and cooled to reduce the risk of contamination or spoilage. Storing grain below a 14.5% moisture content is critical in preserving its quality. In unpredictable seasons, harvesting wheat with a moisture content of more than 16% may be justified in order to protect grain quality.
• The process of drying grain is costly. With hot air drying, relatively high temperatures can be used without threatening grain quality. Dryer air temperatures must not exceed 60°C while grain temperature should not exceed 50°C otherwise the protein could become denatured, resulting in bread which will not rise. Using ambient air (i.e. unheated) to dry grain can be cheaper, but takes longer and there is a risk of fungi growth, leading to mycotoxin formation.
• Grain will be relatively warm post-harvest, ideal for insect breeding. Grain is a good insulator and loses heat very slowly. Grain must therefore be cooled rapidly to prevent pest increase and reduce relative humidity. Much less air (about one tenth) is needed to cool grain than to dry it. It can be achieved at minimal cost by low volume aeration of stored crops. Good cooling practice can protect grain quality. An airflow of about 10m3/hour/tonne is needed for cooling, taking into account grain volumes, insect breeding rate and amount of cool air available after harvest. For wheat harvested in the summer, the aim is to achieve a grain temperature of 15°C within 2 weeks and 5°C by December. Grain harvested at high temperatures should be cooled if it is to be stored for over a week to prevent heat damage to proteins.

Monitoring

• It is critical to regularly inspect stored grain for insects and mite infestations as well as monitoring temperature.
• Sampling is necessary to determine quality. While time-consuming, it must be carried out thoroughly.

The storage business

In the UK, the majority of cereals are stored in modern on-farm stores. Smaller but significant quantities go directly from the combine harvester to co-operative and merchants’ stores. Some farmers pay to be part of a co-operative which jointly own storage and drying facilities. They pool all their grain together and use combined resources to market and sell the grain. Different varieties of wheat are held separately wherever possible so that farmers and traders can meet the specifications of buyers.

Storage can be an expensive business. The main cost will be the store itself (either rented or bought) but other factors will be labour and supervision, pest control and, sometimes, storage and spillage losses. These costs will vary according to the climate, the amount of pests, and even the cost of the capital purchases.

Storage is the subject of on-going research, into areas including:

• pest management systems
• rodent control programmes
• reduction in the use of synthetic insecticides and fumigants
• insect behaviour
• developments of grain varieties that are resistant to pests
• grain storage design and grain moisture and temperature management.

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