Changes in Intergranular Air Properties and Processing Quality of Paddy Stored in a Large Cooled Warehouse

Abstract

This study investigated the relationship between the intergranular air properties of grain bulk and the quality of Japonica paddy stored in a large warehouse cooled by air conditioning (A/C) during oversummering. The psychrometric properties of the intergranular air such as relative humidity, humidity ratio, and wet-bulb temperature, were calculated by a software module. The 2569 tonnes of paddy with 14.5% moisture content (wet basis) was stored in a warehouse in Qihe County, Shandong Province, China, from 16 December 2019 to 9 September 2020. The grain temperature increased more rapidly near the top surface than in other layers of the paddy bulk, reaching the set temperature of 23 °C under A/C cooling, which started from storage day 174 (June 8, 2020). Two 14 kW A/C units (5.5 W t−1 paddy) were sufficient to maintain the set temperature of 23 °C in the headspace. The total electricity consumption was 9.2 kWh t−1 in the two cooling periods (June 8–August 10 and August 28–September 9). When the top surface was cooled by A/C, moisture transferred upwards from the bottom to top surface of the grain bulk, which created favorable conditions for insect growth and the whole grain bulk was fumigated from August 11 to 27. The quality indicators measured in different bulk layers did not change significantly during summer. Regression analysis shows that the percentages of milled rice and head rice, and the taste values and taste panel scores were significantly influenced by the cumulative intergranular air parameters in the paddy bulk. The results suggest that the cumulative intergranular air properties of the grain bulk are useful indicators for assessing the status of paddy stored in a large cooled warehouse.