Long-term storage of wheat—III: Some changes in the quality of wheat observed during 16 years of storage

In 1957 1-tonne lots of each of two different types of pest-free dry wheat, Manitoba and Cappelle, (moisture content 11·9 and 12·6% respectively) were placed in bins. The influence of low temperature (4·5 ± 0·5°C) and low oxygen concentration (<2% by vol) during storage, on the grain quality, was contrasted separately and in combination with ambient levels of each. Over a period of 16 yr there has been no significant changes in the mean moisture contents of the wheats. The viability of wheats stored at low temperature has remained at about 96%, but that exposed to ambient temperature fell to 39% for Manitoba and to 14% for Cappelle. Free fatty acid values increased with time in both types of wheat, the rate of increase in the bins at ambient temperature being about twice that in the cooler bins. The wheats yielded satisfactory bread throughout. However, the need to add 20 ppm of potassium bromate, and 224 ppm of fungal alpha-amylase to correct a deficiency of natural alpha-amylase, became apparent after 8 yr storage.

There was no growth of micro-organisms in samples of the dry wheats stored for periods up to 10 yr in tubes pushed into the surface of the main bulks of wheat. Except for Aspergillus, the fungi and bacteria survived better at 4·5°C than at ambient temperature. Numbers of Aspergillus remained almost unchanged at ambient temperature over the whole decade, so the survival of Aspergillus over a considerably longer period under all the conditions studied is quite probable. Some bacteria might also be expected to survive for a long period under all the conditions studied while many other species of fungi might survive at low temperature.

Oxygen concentration had little influence on the changes during storage of either the wheat itself or on the survival of the microflora. Restriction of oxygen however, prolonged germinative capacity at ambient temperature for about four years. Low temperature was more effective generally, in reducing adverse changes than low oxygen.