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2016/6/11 1 Moisture Adjustment
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1. Objectives 2. Collection and Preconditioning of Grain Reference Samples 3. Arrangement of Moisture Content 4. Homogenization and Low Temperature Storage 5. Precautions for Use 2016/6/11 2
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Adjusting the moisture content of reference samples Samples are to be used for (1) development of calibration curves of grain moisture meters (2) verification of commercial grain moisture meters. 2016/6/11 3
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Usually minimum number of samples are prepared. (1) Selection of samples 1 Cover more than 70% of the varieties. 2 Cover more than 70% of growing places. 3 Be harvested within one year. 4 Circulation of grain in the market be taken into account. 5 Kind, variety, type, place of sampling, place of product and year of harvest be recorded. 6 More than 4 times of the minimum weight required be collected. 7 Be collected immediately after harvesting. 2016/6/11 4
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THE AMOUNT OF SAMPLE Original Sample Ag2 x Ag Arranged Sample Ag 2 x Ag 2 x 2 x Ag = 4 x Ag 5
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(2) Preliminary Procedures for Conditioning 1 Clean the samples by manual sieving or the mechanical separator Pick out foreign substances 2016/6/11 6
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Manual sieves (ISO 5223) ・ long rounded apertures of 1.50mm width for rice; ・ long rounded apertures of 1.90mm width for rye, durum wheat, bold rice ; ・ long rounded apertures of 2.00mm width for wheat; ・ long rounded apertures of 2.20mm width for barley; ・ round holes of 4.50mm diameter for maize 2016/6/11 7
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2 Original moisture content is measured by a verified grain moisture tester. three or five times average. 3 Mixing well and equally divided. 2016/6/11 8
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AN EQUILIBRIUM MOISTURE CONTENT ON WETTING AND DRYING PROCESS Fig.1 Equilibrium moisture contents on brown rice under wetting process and drying process at 20 ℃ and 70%RH. The equilibrium moisture content is usually different between wetting process and drying process. This phenomenon is called as the “hysteresis.” The moisture content of grains, set at a given thermo-humid condition, shall be driven to an asymptotical and stable state, denoted as the “equilibrium moisture content.” 10
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EQUILIBRIUM AND HYSTERESIS Fig.2 Moisture sorption isotherm for cornstarch The equilibrium moisture contents have the hysteresis in the intermediate of the humidity condition. A given thermo-humid condition drives the grain moisture to a certain equilibrium moisture content. 11
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Development and evaluation of wide range moisture content reference samples Adjustment of Moisture Content by Drying 1 Check the original moisture content 2 Dry samples (in the room or by the oven) 3 Check moisture content by weighing 4 Mix sample well to homogenize 5 Put data label 12
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(2) Adjustment of Moisture Content by Moistening 1 Check original moisture content 2 Moisten samples by a moist bath 3 Elevate moisture content up to 2% higher than the target by checking the weight 4 Dry sample slightly by an oven 5 Mix sample well to make homogenize 6 Put data label 13
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1. Adjustment of Moisture Content by Drying M x < M 0 M 0 original moisture content W 0 g M x target moisture content W x g W x g=W 0 x (100- M 0 )/(100- M x ) 2. Adjustment of Moisture Content by Moistening M 0 < M y M 0 original moisture content W 0 g M y+2 target moisture content plus 2% W y+2 g M y target moisture content W y g W y+2 g=W 0 x (100- M 0 )/(100- M y+2 ) W x g=W 0 x (100- M 0 )/(100- M x ) 14
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Minimize dispersion of the moisture content and keep the sample quality. (1) Homogenization (2) Low temperature storage 2016/6/11 17
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To minimize the dispersion among grain kernels of the samples by diffusion of water molecule. Water molecules are exchanged among grain via ambient water vapor. It is necessary to seal the bag containing a sample. 2016/6/11 18
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The lower temperature the quality of the samples is stored, the better the quality is obtained. Freezing should be avoided since the ice crystal damage the grain tissue and change the physical properties. It is impossible to maintain the quality of sample forever even if they are stored at 5˚C. 2016/6/11 19
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When a sample stored for a long time at a low temperature is to be used for the measurement of moisture content at room temperature, the sample bag should not be opened immediately after taking the sample out of the refrigerator. Samples are equilibrated overnight to room temperature. High moisture samples need the time at least 4 hours. 2016/6/11 20
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THANK YOU FOR YOUR ATTENTION!
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