Preserving grain quality in long-term storage

Partners:
Zimbabwe grain companies

Problem:
Large-scale storage is an essential component in both grain marketing chains and food security systems.  Grain and other durable commodities may be stored for relatively long periods and subsequent quality deterioration is a common problem leading to nutritional and financial losses.

Achievements:
Two research outputs offer opportunities for better retention of the quality of grain kept in long-term storage, favouring better food security, increasing the options for strategic storage and improving opportunities for grain to be marketed at the most favourable times. 

In the 1990s, improved methods of long-term storage of maize were developed to prevent stackburn.  This is characterised by brown discolouration due to the build-up of heat in the interior of bag stacks and can affect local or imported maize grain, especially when kept in polypropylene sacks.  The improved method of storage involves the use of passive ventilation and additionally, for grain stacks maintained out of doors, a moisture absorbent layer between grain and tarpaulins. 

For milled rice, quality decline can be rapid in hot humid climates but if bags stacks are sealed into plastic envelopes flushed with phosphine or carbon dioxide then quality can be maintained for several years, the same technique may also have applications for small-scale storage of high value commodities such as spices, coffee etc.  Although initially more expensive than conventional storage methods, sealed stack storage becomes cost effective when used for relatively long periods.