Improvement of the drying oven method for the determination of the moisture content of milk powder

For the determination of the moisture content using both the IDF Provisional Standard 26A: 1993 and the EU method (1979) a test portion of milk powder is dried at 102 degrees C until constant mass is obtained. The values for repeatability and reproducibility, established in 1987 by the 'Methods of Analysis Group' of Asfalec by means of an international collaborative study, using the IDF Standard, were unacceptably high. The variation of the moisture content of milk powder determined according to these methods is especially affected by the relative humidity of the air in the laboratory where the test is carried out. COKZ has developed a test apparatus for drying test portions of milk powder under adjustable, standardized conditions regarding temperature and relative humidity. With this apparatus the influence of the drying temperature and time, relative humidity and flow of air used for drying the test portion on the level and variation of the moisture content was studied. A constant mass of the test portion is obtained after 4-5 h at a drying temperature of 87 degrees C and by flushing dry air (0.01 mg H2O L-1) through the test portion. Under these conditions a moisture content is obtained that corresponds well with the moisture content determined by the EU method. (C) 1998 Elsevier Science Ltd. All rights reserved.