Storage of pelleted wheat middlings in farm bins

Abstract

The objective of this study was to describe the storage-related characteristics of pelleted wheat middlings (WM) and to test strategies for maintaining the desirable bulk flow characteristics of the pellets during storage in farm bins during warm, humid weather. Cattle producers located close to flour mills purchase pelleted WM in the summer when prices are low and store them into the winter when they are needed. Four Kansas flour mills were surveyed on four sampling dates to characterize samples of pelleted WM relative to storage-related factors, e.g. moisture content, bulk density, bulk flow characteristics, and mycological conditions. Physical simulations were done in environmental chambers to determine the cause of aggregation (loss of bulk flow characteristics) and develop techniques for controlling aggregation and mold growth. Findings were verified at a larger scale in farm bins. Pelleted WM had twice the bulk density and a greatly reduced count of storage molds compared to unpelleted WM. Mold counts remained low for at least 6 weeks after pelleting, even with storage at 30°C. The moisture contents of WM pellets ranged from 128 to 149 g/kg with a mean of 140±5 g/kg in March, April, and May, but the mean moisture content was reduced to about 132 g/kg by June. Pelleted WM aggregated when stored at high moisture and temperature even if the level of mold infection was low. Mold growth that caused heating and aggregation was observed at higher temperatures when pellets remained moist, but the species of molds predominating were not those associated with the production of aflatoxin. Drying and cooling the pellets by means of near-continuous summer aeration prevented mold growth to a large extent and minimized the effects of aggregation. Spout lines, areas where fine material accumulated directly beneath the fill spout, were associated with mold growth, heating, and impedance of airflow.