EXPERIMENTS ON THE AIRTIGHT STORAGE OF DAMP GRAIN

Airtight storage as a means of preventing deterioration of damp grain was studied both on a laboratory scale and in 10-ton bins, at grain moisture contents from 17 to 24%.
Except when containers leaked, there was no development of mould, and the grain was bright and free-flowing, even after prolonged storage, at high moisture content. The grain remained mould-free after a bin was opened several times and small quantities of grain run out in cool weather. Such grain, removed from hermetic conditions and stored in sacks in an unheated building, showed no mould development for several weeks.
With prolonged hermetic storage or at high moisture content the grain developed a sour-sweet smell and taste which when extreme were not entirely removed by subsequent airing or drying.
There was no spontaneous heating; the grain in the 10-ton bins reflected the mean temperature of the surroundings.
The oxygen in the intergranular air was reduced to a low level and replaced by carbon dioxide within a few days or weeks, according to the moisture content and temperature of the grain. At moisture contents of 16% and above, appreciable positive pressure developed inside the containers. The carbon dioxide concentration rose to 90–95% at grain moistures of 22–24%, 70–75% at 19%, 50% at 18%, and 35–40% at about 17% moisture content. The change from aerobic to anaerobic activity was marked by a reduction in the rate of production of carbon dioxide. With grain of less than 14% moisture content, the rate of respiration was slow, the carbon dioxide concentration being only about 2% after 18 months' storage. As long as oxygen remained, the apparent respiratory quotient was consistently between 0.6 and 0.7, whatever the moisture content of the grain.
This work formed part of the programme of work of the Pest Infestation Laboratory.