International Association for Cereal Chemistry (ICC) - ICC-Standard No. 109/1
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Determination of the Moisture Content of Cereals and Cereal Products (Basic reference method).
In the case of maize (and whole maize meal) the method for the determination of moisture content differs in some respects from the method for other cereals (and cereal products). In the Standard the variations are indicated by two columns in the description of the method; the right-hand column applies to maize and the left-hand column to other cereals and cereal products.
Cereals and cereal products (+) Maize and whole maize meal (+) For the sake of simplicity, in following paragraphs the word "product" is used to mean a cereal as well as a cereal product
This method can be taken as the standard for the development of methods which are specifically suited to the practical determination of the moisture content of wheat, rice (hulled paddy), barley, maize or whole maize meal, millet, rye and oats, as grains, ground grains, semolina and flour
It is not to be used for the settlement of commercial disputes.
The moisture content of a product is defined as the loss in weight sustained by the material under the conditions specified in this Standard, expressed as a percentage of the weight of the original sample.
Measurement of moisture loss when the material, ground if necessary without chan ICC-Standard No. 109/1 ge of moisture content, is equilibrated in an anhydrous atmosphere at a temperature between 45° and 50°C and at a pressure of 1.3... 2.7 kPa (10...20 mm Hg).
Analytical balance (min. precision: 0.1 mg, max. load: 200 9).
Apparatus which reduces the pressure to 1.3...2.7 kPa (10...20 mm Hg) (e.g. water jet pump).
Corrosion-proof metal dish watertight cover. Its utilisable surface should allow a sample distribution of 0.3 9 per square centimetre.
Glass or porcelain bowl.
Desiccation tube made of glass (2) with one end closed and the other end provided with a semi-capillary connecting tube and a tap for producing a vacuum. Both ends are closed with a ground stopper. After drying, the sample is cooled in the desiccation tube eliminating the need for a desiccator at this stage.
Electric drying oven with temperature regulation or other apparatus which raises the temperature of the chamber containing the sample dish to between 45° and 50°C.
Air-drying system: washing apparatus containing analytical grade sulphuric acid (d20 K 1830 kg/m³), and connected to a tube containing analytical grade phosphorus pentoxide (P2O5) dispersed on fibreglass.
Desiccator with active drying agent (phosphorus pentoxide). Vacuum bell-jar or desiccator large enough to cover the metal dish
According to I.C.C. Standard Method No. 101.
The weighing should be carried out to a precision of 0.0002 9.
Preparation of the sample
8.1.1 Products which do not require grinding.
Products with a particle size of 1.7 mm or less, with well than 10% by weight larger than 1 mm and more than 50% by weight smaller than 0.5 mm, need not be ground before the determination.
8.1.2 Products requiring grinding.
If the particle size of the sample does not correspond to that of 8.1.1, grinding, with or without preliminary conditioning, is necessary.
22.214.171.124 Grinding without preliminary conditioning.
This is carried out in the case of products the moisture content of which does not vary during grinding; in general these are grains with a moisture content of 7...17%(7...15% for oats). 9...15%
The grinding apparatus is set up so that the particle sizes obtained correspond to those in 8.1.1. A small quantity of the products is ground and discarded. Approximately 3.5 g 30 g of the sample is then ground rapidly. The powder is quickly homogenised with a spatula.
The ground product ca.3 g of the ground product is placed in the previously dried and tared metal dish (6.4.); the dish is quickly covered and weighed (M2).
The determination is then carried out.
When using pin- or hammer-mills, the interval between sampling and weighing before drying must be less than 2 or 3 min.
126.96.36.199 Grinding with preliminary conditioning.
Products which are too dry (m.c less than 7%) or too moist (m.c. less than 9%) (m c. above 17%, or 15% for oats) (me above 15%) must be moistened or dried, respectively, before grinding. In the case of products with a moisture content below 7% below 9% the sample is moistened by being brought into an atmosphere such that the final moisture content is between 7 an 17% (for oats between between 9 and 15% 7 and 15% and for other cereals preferably between 9 and 15%)
The most frequent need is for pre-drying of grain which is carried out generally when the moisture content exceeds 17% exceeds 15% in order to bring it within the limits of 7...17% (for oats 7...15% and for 9. 15% other cereals 9...15% if possible). 3.5 9 of the sample in whole grains (Mo) is weighed accurately and the drying process carried out according to 8.3., however the drying time is 1 1/2 h to max 2 h and a renewal of the phosporus pentoxide is not necessary. 100 9 of whole grains (Mo) is accurately measured into the metal dish (6.4.); the metal dish is placed under the vacuum bell-jar (6.9.) in which there are petri dishes with phosphoric anhydride in a ca. 1 cm thick layer, the vacuum bell-jar is closed and the pressure gradually reduced to 1.3...2.7 kPa (10 to 20 mm Hg), in order to prevent spattering of the substance, (e.g. by inserting a semicapillary tube). The connection with the device producing the vacuum is closed. The sample remains at laboratory temperature until its moisture content is between 9 and 15% (usually 2..4 days). The phosphorus pentoxide is renewed each time it becomes hydrated. The atmospheric pressure in the vacuum belljar is' restored by slowly introducing the air which has passed through the drying system.
The sample must be held at laboratory atmosphere for at least 24 h.
The pre-dried sample is accurately weighed (M') and some 30 9 of it is immediately ground; the powder is homogenised rapidly with a spatula. 3 9 of it is weighed accurately into the determination dish (6.4.). The interval between the two weighings (M' and M2) should be less than 2 min.
After conditioning the. sample is accurately weighed (M') and immediately ground in the previously set up grinding apparatus (6.3.). The ground product is placed in the metal dish (6.4.). The sample is weighed again, and the interval between the two weighings (M, and M2) may not exceed 2...3 min. The determination is then carried out.
Sample for analysis
8.2.1 In the case of products not requiring grinding (see 8.1.1.) quickly
- place some 3 9 of the substance in the metal dish (6.4.) which has, after being in the srying cupboard (6.7.), been tared, and cooled to laboratory temperature in the dessiccator (6.9);
- close the dish and weigh (Mo).
8.2.2 In the case of products which require grinding (see 8.1.2.), the ground product (see 188.8.131.52. and 184.108.40.206.) in the closed and weighed metal dish (4.4.), is used as the sample for analysis.
The open dish (6.4.) containing the sample is placed inside the glass tube (6.6.); a dish (6.5.) containing a 1 cm thick layer of phosphoric anhydride is placed next to it. The two ends of the desiccation tube are joined together; the pressure in the enclosed space is gradually reduced to between 1.3 and 2.7 kPa (10...20 mm Hg), to avoid spattering of the substance (e.g. by inserting a semi-capillary tube). The connection with the device producing the vacuum is closed. The part of the tube containing the dish is heated to 50°C in the drying oven (6.7.).
As soon as the phosphoric anhydride cakes it must be renewed, after which atmospheric pressure is restored inside the desiccation tube (6.6.) by introducing slowly, using a semi-capillary tube, air which has passed through the drying system (6.8.). The desiccation tube is closed again and vacuum drying carried out at 50°C as before. After cat 100 h the tube is removed from the drying oven and cooled to laboratory temperature. Atmospheric pressure is restored inside as previously indicated. The dish is rapidly removed, covered, and weighed immediately (M3)
Dehydration is continued until constant weight is attatined (less than 0.00006 9 difference between two weighings carried out 48 h apart).
The determination must be performed at least twice.
9. PRESENTATION OF RESULTS
Calculation method and formulas
The percentage moisture content of the product is
9.1.1 without preconditioning
9.1.2 with preconditioning
M0 = initial weight of the original sample in 9 (whole grains before conditioning in the case of
a determination with preliminary drying or wetting),
M1 = weight of the original sample in 9 after conditioning,
M2 = weight of the sample in 9 after grinding,
M3 = weight of the sample in 9 after complete drying.
The determination must be carried out at least twice. The arithmetic mean of the determinations, if the condition for the accuracy of the determination (9.2.) is fulfilled, is taken as the result. The result is rounded off to the nearest 0.05 9 water per 100 9 sample.
Accuracy of the determination
The difference between the results of two determinations is calculated to the nearest 0.01%. The difference between the results of these determinations, which have been carried out simultaneously or in quick succession by the same person, should not exceed 0.10 9 water per 100 9 sample. If this is not the case, another duplicate determination must be performed.
Note: with some practice, differences of less than 0.05 9 water per 100 9 sample can be achieved in one laboratory.
10. EXPERIMENTAL REPORT
The experimental report should give the method used and the result obtained. In addition, all details of the procedure which are not provided for in the present ICC-Standard or are optional must be mentioned, and any incidents which might have influenced the result.
The experimental report must contain all the data necessary for complete identification of the sample.
The moisture content range given for conditioning the cereal grains before grinding is suitable for a temperature of approximately 20°C and relative humidity of 40 to 70% in the laboratory. Under other atmospheric conditions the m.c. range would have to be changed.
The length of pre-drying time should only be thought of as a guideline. It is necessary to check whether the desired conditioning can be achieved in this time with the equipment and type of cereal being used.
Discolouration of the surface of the phosphorus pentoxide indicates the loss of traces of volatile organic substances from the product being tested. This phenomenon serves as a warning. If in the case of certain adulterated products the discolouration becomes very marked, the heating temperature should be reduced. The phosphorus pentoxide should be renewed as soon as it cakes at the surface.
The above-described basic reference method for the determination of moisture content in cereals and cereal products was worked out to guarantee the elimination of the entire moisture content of the product, as water addition and removal experiments show. At the same time any chemical change in the substance, especially oxidation or loss of volatile organic substances, is avoided. Given the present state of knowledge this method offers a practical way of measuring the moisture content of cereals and cereal products.
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