Heat effect on rheology of light- and dark-colored honey

The effect of temperature and time of constant temperature heating (t(CTH)) on the rheological properties of light and dark types of honey was examined. Honey samples were heated up to 40 degreesC, 60 degreesC, 80 degreesC or 94 degreesC, and hold for 5, 10 or 20 min, and their viscosities were then measured either immediately at the heating temperature or after being cooled overnight, where measurements were carried out at 25 degreesC and 35 degreesC as a function of the shear rate. The types of honey used were identified via assessing the source of the nectar using pollen analysis (Melissopalynology). It was found that both honey types behave like a Newtonian fluid regardless of the conditions of heating. The time of heating required to reach the desired ultimate temperature correlates with the water content of the fresh, untreated sample. A light-colored, low water-content, heat-treated honey showed a change in viscosity only at higher heating temperatures when compared with the fresh untreated control sample. On the other hand, a dark-colored, heat-treated honey showed a change in viscosity at all levels of heating temperature. In general, the viscosity of a heat-treated honey increases with increasing ultimate heating temperature and tCTH. (C) 2001 Elsevier Science Ltd. All rights reserved.