The microbiology of moist barley storage in unsealed silos

SUMMARYThe microflora of moist barley grain and whole‐crop barley silage stored in top‐unloading, unsealed concrete‐staved silos on six farms in England depended on the initial water content of the grain (23–58%), method of covering the grain, and the rate at which it was unloaded. Fungi and actinomycetes were fewest when the initial water content was more than 30%, and the grain was covered first with a layer of wilted grass, and then a plastic sheet. During unloading, the uppermost layer of grain remained in good condition provided 7.5 cm was removed daily.With an inefficient top‐seal, the top grain heated and became mouldy, as it also did when unloading was slow. As the rate of unloading slowed, heating increased, and a characteristic succession of fungi and actinomycetes developed. With unloading at 7.5 cm/day or more, only yeasts, chiefly Endomycopsis chodatii Wickerham and Hansenula anomala (Hansen) H. & P. Sydow, were abundant, but at slightly slower rates of unloading Penicillium spp. also became common. Both these groups became less common as unloading was slowed further and were replaced, first by Absidia spp. and Mucor pusillus Lindt, then Aspergillus fumigatus Fres., Humicola lanuginosa (Griffon & Maublanc) Bunce, Micropolyspora faeni Cross, Maciver & Lacey, and Thermoactinomyces vulgaris Tsiklinsky as the heating increased. The number of spores (including bacterial cells) that could be removed from samples by blowing air ranged from 0.4–428 times 106/g dry weight of grain. Whole‐crop barley silage contained 2.9–132 times 106spores/g dry weight. Similar species were isolated from whole‐crop silage as from grain. Little moulding occurred deeper than 30 cm below surface of the grain.Concentrations of airborne spores were estimated periodically during two seasons. There were always more airborne spores than is usual in outdoor air. Without disturbance the silos contained 106‐107 spores/m3 air, but when mouldy grain was unloaded concentrations increased to a maximum of 2860times106 spores/m3 air; more than half of these were bacteria and actinomycetes and a quarter Aspergillus flavus Link. Potentially pathogenic fungi and actinomycetes were frequent, particularly when they also occurred in the grain or capping materials for spontaneous heating. Some probably survived in dust deposits and were resuspended during unloading. Airborne spores were frequent around the silos when grain was unloaded and rolled. Workers should wear efficient dust respirators at these times and while inside silos.