ISO 6540:2021 pdf download – Maize — Determination of moisture content (on milled grains and on whole grains).
4.2.3 Grinding mill, having the following characteristics: a) made of material that does not absorb moisture; b) easy to clean and having as little dead space as possible; c) enabling grinding of 30 g of maize grains to be carried out rapidly and uniformly, without appreciable development of heat and, as far as possible, without contact with the outside air; d) adjustable so as to obtain particles of the dimensions indicated in 4.4.1. 4.2.4 Metal boat, without lid, with an effective surface area enabling 100 g of maize grains to be distributed in a single layer. 4.2.5 Metal capsule, of suitable dimensions, non-corrodible under the test conditions, or, failing this, a glass dish, with a sufficiently tight-fitting lid, and having an effective surface area such as to allow distribution of the test portion with no more than 0,3 g per square centimetre. 4.2.6 Constant-temperature oven, electrically heated, adjustable between 60 °C and 80 °C, and with adequate ventilation. 4.2.7 Constant-temperature oven, electrically heated, capable of being controlled in such a way that the temperature of the air and of the shelves carrying the test portions is within the range of 130 °C to 133 °C in the neighbourhood of the test portions, in normal working condition. The oven shall have a heat capacity such that, when initially adjusted to a temperature of 131 °C, it can again reach this temperature in less than 45 min (preferably in less than 30 min) after insertion of the maximum number of test portions that can be dried simultaneously. The effectiveness of the ventilation shall be determined using durum wheat semolina, with a maximum particle size of 1 mm, as the test material. The ventilation shall be such that, after inserting all the test portions that the oven can hold and drying at a temperature of 130 °C to 133 °C, the results after a heating period of 2 h and then a further 1 h will not differ by more than 0,15 g of moisture per 100 g of sample.
4.4.2.2 Grinding without pre-conditioning For products that are not likely to undergo variations in moisture content in the course of grinding (in general, products with a moisture content between a mass fraction of 9,00 % and 15,00 %, see 4.8), carry out grinding without pre-conditioning. Adjust the grinding mill ( 4.2.3 ) to obtain particles of the dimensions indicated in 4.4.1. Then quickly grind about 30 g of the laboratory sample, mix with a spatula and proceed immediately as specified in 4.5.1. 4.4.2.3 Grinding with pre-conditioning Products that are likely to undergo changes in moisture content in the course of grinding (in general, products with a moisture content more than a mass fraction of 15,00 % or less than a mass fraction of 9,00 %) shall be pre-conditioned to bring their moisture content to between a mass fraction of 9,00 % and 15,00 %, see 4.8) before grinding. If the moisture content is greater than a mass fraction of 15,00 % (which is the more frequent case), weigh, to the nearest 0,1g, about 100 g of the laboratory sample in the metal boat (4.2.4), place this in the oven ( 4.2.7 ) controlled at between 60 °C and 80 °C, and leave it for the time necessary to bring the moisture content to between a mass fraction of 9,00 % and 15,00 % . Take the boat out of the oven and allow it to stand in the laboratory atmosphere for the time necessary (at least 2 h) for the pre- conditioned sample to return to the laboratory temperature and for the moisture distribution to be relatively uniform. During this rest, it shall be ensured that no addition or withdrawal of material is made to the contents of the boat. If necessary, cover it with a sheet of paper but not with a lid, since this could limit the exchange of moisture between the air and the grain. After conditioning, weigh the sample to the nearest 0,1 g, then, proceeding rapidly, grind about 30 g of this product. Mix using a spatula.
