39D-1

H. D. ISENGARD, Institute of Food Technology, University of Hohenheim, Garbenstr. 25, D-70593 Stuttgart, Germany and D. Schultheiss.

Honeys must not contain too much water to prevent them from microbiological spoilage. Water content is usually measured via the refractive index (RI). From the value measured the water content is calculated by an empirical formula or looked up in "translation" tables. Creamy honeys must be heated before analysis, a procedure that may result in a loss of water and makes a comparison with liquid honey measurements at room temperature difficult. Another problematic point is that the composition of the solid content, which in fact is determined by RI measurements, varies from one sort of honey to another. The formula used for calculation is therefore necessarily not equally correct for every honey.

The objective of this work was to establish a generally applicable method to determine the true water content of honeys.

A variation of the Karl Fischer (KF) titration was found to be applicable on all of the more than fifty honey samples from different countries and from various biological sources. The results were very precise and the titration curves indicated a complete and correct detection of the water. The results were compared to those obtained by RI measurements. It could be shown that creamy honeys do loose up to 0.2% water during the necessary preheating and, thus, that RI measurements do not yield the original water content. In most of the cases the KF results were higher (0.5% in average). In a few cases, however, the RI results were higher (up to 1%). This seems to depend on the botanical origin of the honeys and indicates that the empirical formula is not equally applicable on all sorts of honey.

The investigation shows that RI results have an accuracy of only 1%. For correct analyses of the true water content the KF titration should be applied.