Influence of bulk density on grain moisture meter
Bulk density is one of the comprehensive indicators reflecting the characteristics of grain, and it is also the main indicator for grading grain at home and abroad and evaluating the quality of grain technology [4] . According to the bulk density, the quality of a certain volume of grain pile and the storage capacity required for a certain quality of grain can be calculated, which has certain practical significance for grain storage and transportation [2] . In addition, the test density is also one of the important basis for calculating the theoretical flour extraction rate of wheat [6] .
Bulk density refers to the mass of grain and oil seeds per unit volume. The grading of many grains such as wheat and corn in my country is based on bulk density. Grain bulk density is determined by the size, shape, uniformity, depth of ventral groove, fullness, endosperm texture and other aspects of the grain [6] . Generally speaking, samples with mature and plump grains, compact structure, small grains, and low water content have larger bulk density [5]; otherwise, smaller bulk density [5]. In particular, the water content in the grain affects the size of the bulk density, which is generally a negative linear relationship. This is mainly because the proportion of water is smaller than that of grain. At the same time, water also affects the volume of the grain. The quality inside is small [8].
Moisture is an important component of grain, it not only affects the change of grain, but also affects the processing, storage and production of grain [1]. Grain with too much moisture is prone to heat and mildew, and an appropriate amount of moisture can ensure the smooth progress of grain processing and food production. There are two forms of moisture in food: free water and bound water. When the grain moisture reaches 14% to 15%. [2] Free water begins to appear. When the grain moisture is below 13.5%, it is generally regarded as bound water [8] . Free water in grain grains is very unstable, and its existence is very unfavorable to the safe storage of grains. Only when the water content of grains drops to the bound water range, grain grains can be in a dormant state, and life activities can be minimized. The limit is conducive to the storage of grain [6].
In order to increase the stability of grain storage, purchasing and storage enterprises must take measures to reduce the moisture content of the purchased high-moisture grains. As the moisture decreases, the bulk density will also change. Since the test density is the grading index of wheat and is directly related to the wheat price, it is of great significance to study the relationship between moisture change and test density [6].
