Economic and Social
10 December 2002
Original: ENGLISH and FRENCH
ECONOMIC COMMISSION FOR EUROPE
COMMITTEE FOR TRADE, INDUSTRY AND
Working Party on Agricultural Quality Standards
Fifty-eighth session, Geneva, 29 to 31 October 2002
REPORT OF THE FIFTY-EIGHTH SESSION
ANNEX II: DETERMINATION OF THE MOISTURE CONTENT
FOR DRY PRODUCE (NUTS)
Note by the secretariat: The revised text of Annex II to the standard layout for dry and dried produce has been accepted by the Working Party for adoption. It will be automatically included in all relevant standards.
DETERMINATION OF THE MOISTURE CONTENT FOR DRY PRODUCE (NUTS)
METHOD 1 - LABORATORY REFERENCE METHOD
1. Scope and application
This reference method serves to determine the moisture and volatile matter content for both inshell nuts and shelled nuts (kernels).
This method is based on the method prescribed by ISO: ISO 665-2000 Oilseeds - Determination of moisture and volatile matter content.
Moisture content and volatile matter content for dry produce (inshell nuts and shelled nuts): loss in mass measured under the operating conditions specified in ISO 665-2000 for oilseeds of medium size (see point 7.3 of ISO 665-2000). The moisture content is expressed as mass fraction, in percent, of the mass of the initial sample.
For whole nuts, when moisture content is expressed both on the whole nut and on the kernel, in cases of dispute between the two values, the moisture content value of the whole nut takes precedence.
Determination of the moisture and volatile matter content of a test portion by drying at 103 ± 2º C in an
oven at atmospheric pressure, until practically constant mass is reached.
5. Apparatus (see ISO 665-2000 for more details)
5.1 Analytical balance sensitive to 1 mg or better.
5.2 Mechanical mill.
3 mm round-holes sieve.
Glass, porcelain or non-corrosive metal containers, provided with well-fitting lids, allowing the test portion to be spread to about 0.2 g/cm 2 (approximately 5 mm height).
5.5 Electric oven with thermostatic control capable of being regulated between 101 and 105º C in normal operation.
5.6 Desiccator containing an effective desiccant.
Follow the operating conditions as specified in ISO 665-2000 for oilseeds of medium size (point 7 and 7.3 of ISO 665-2000), but with the following specific modifications, concerning the preparation of the test sample.
Although ISO 665-2000 sets up one initial period of 3 hours in the oven set at 103 ± 2º C, for nuts it is recommended one initial period of 6 hours.
6.a Determination of the moisture and volatile matter content of kernels:
For shelled nuts, homogenize the laboratory sample and take a minimum of 100 g of kernels as a test sample.
For inshell nuts, take a minimum of 200 g and, using a nutcracker or hammer, remove the shells and fragments or particles of shell, using the rest as a test sample. The kernel skin (cuticle or spermoderm) is included in the test sample.
Grind and sieve the test sample until the size of the particles obtained is no greater than 3 mm. During the grinding operation, care should be taken to avoid the production of a paste (oily flour), the overheating of the sample and the consequent loss of moisture content (for example, if using a mechanical food chopper, by successive very short grinding and sieving operations).
Spread evenly over the base of the vessel about 10 g of the ground product as a test portion, replace the lid, and weigh the whole vessel. Carry out two determinations on the same test sample.
6.b Determination of moisture and volatile matter content on whole nuts (shell plus kernel):
Homogenize the laboratory sample and take a minimum of 200 g of nuts as a test sample. Remove all the foreign matter (dust, stickers, etc.) from the test sample.
Grind the whole nuts using either a Rass Mill, a Romer Mill or a Brabender apparatus or similar, without overheating the product.
Spread evenly over the base of the vessel about 15 g of the ground product as a test portion, replace the lid, and weigh the whole vessel. Carry out two determinations on the same test sample.
7. Expression of results and test report
Follow all the instructions as specified in ISO 665-2000 (point 9 and 11) for method of calculation and formulae, and for test report, without any modification. 1
For conditions of repeatability and reproducibility apply specifications of ISO 665-2000 (point 10.2 and 10.3) for soya beans.
METHOD 2: RAPID METHOD
Determination of the moisture content using a measuring apparatus based on the principle of loss of mass by heating. The apparatus should include a halogen or infra-red lamp and a built-in analytical balance, calibrated according to the laboratory method.
The use of apparatus based on the principle of electrical conductivity or resistance, as Moisture Meters, Moisture Testers and similar, is also allowed always at condition that the apparatus has to be calibrated according with the laboratory reference method for the tested product.
2.1 Mechanical mill or food chopper.
2.2 3 mm round-holes sieve (unless indicated otherwise by the instructions for use of the apparatus.
2.3 Halogen or infrared lamp with built-in analytical balance sensitive to 1 mg or better.
3.1 Preparation of sample
Follow the same instructions as given for the laboratory reference method (points 6.a and 6.b), unless indicated otherwise by the instructions for use of the apparatus, particularly with regard to the diameter of the fragments.
3.2 Determination of moisture content
Carry out the determination on two test portions of approximately 5 to 10 g each, unless indicated otherwise by the instructions for use of the apparatus.
Spread the test portion over the base of the test receptacle, thoroughly cleaned in advance, and note the weight of the test portion to within 1 mg.
Follow the procedure indicated in the instructions for use of the apparatus for the product to be tested, in particular with regard to the adjusting of temperatures, the duration of the test and the recording of the weight readings.
4. Expression of results
The result should be the arithmetic mean of the two determinations, provided that the conditions of repeatability (4.2) are satisfied. Report the result to one decimal place.
The difference in absolute value between the respective results of the two determinations performed simultaneously or one immediately after the other by the same operator, under the same conditions on identical test material, must not exceed 0.2%.
5. Test report
The test report must state the method used and the results obtained. The report must contain all information necessary for the full identification of the sample.