Studies on Grain Moisture Content Measurements by Air Oven Methods (II)

Investigation on the Methods without the Apparent Loss of Dry Matter

Abstract

We noticed the fact that the following equation did not hold good for some air oven methods of grain moisture measurement, where the apparent loss of dry matter was not taken into considration. Therefore we investigated on improved air oven methods so as to aviod the apparent losses of dry matter.
W_i(1-M_i/100)=W_f(1-M_f/100)
where
W_i: Initial weight of grain
M_i: Initial moisture content of grain (wet basis)
W_f: Final weight of grain
M_f: Final moisture content of grain (wet basis)
The three standard measurement conditions for three air oven methods are shown in the following.
(1) At 105°C for 5 hours with whole grain of about 5 grams
(2) At 105°C for 24 hours with ground grain of about 10 grams
(3) At 135°C for 24 hours with whole grain of about 10 grams
The materials used were wheat, six-rowed barley, two-rowed barley and rough rice.
1. The replicate moisture determinations of samples were within 0.2% throughout all the tests.
When the content of kernels with primary branch and ear breaking in rough rice was below 15%, the representative moisture content of rough rice including kernels with primary branch and ear breaking was able to be regarded as the moisture content of kernels.
For the moisture measurement by the two-stage drying method, there were not effects of tempering period after pre-drying on moisture content values.
2. The weights of samples dried by the methods as shown in (1), (2) and (3) were regard as the defined constant weight regardless of drying time in the air oven.
The defined constant weight means the weight after drying which does not vary over 0.1% during 2 hours of drying time in the air oven.
According to the experimental results by the the methods in which the drying time only is varied in the air oven, the reduction in weight of sample stopped completely after the drying time of 48 hours in (1) and 240 hours in (2). However, the reduction continued deyond 240 hours in (3).
3. Regardless of the kinds of grains and moisture contents, the drying time in the air oven which did not show apparent loss of dry matter was 48 hours in (1), 240 hours in (2) and 48 hours in (3) respectively.
4. It was assumed that the moisture remained yet in the dry matter obtained from the drying period shown in the standard measurement methods, and this moisture was calculated as “the remained moisture content” on the base of the dry matter dried in the air oven during the period mentioned in 3
The relation between the remained moisture content and the measured moisture content was made clear.
For below 15% and above 5% of moisture contents of rough rice, the lower the moisture content the higher the remained moisture content, For the rough rice in (2) and (3) except the range of moisture contents above mentioned, wheat, six-rowed barley and two-rowed barley, the higher the moisture content the higher the remained moisture content.
5. The smallest quantity of apparent loss of dry matter among the methods (1), (2) and (3) was obtained in the case of (3). In order to maintain the apparent loss of dry matter as insignificant as possible in the wide range of moisture contents, the adoption of the two-stage drying method was recomended