Studies of long-term storage of high quality raw sugar

Abstract

Although existing contracts do not provide sufficient economic justification to increase raw sugar quality, the trend of manufacturing better quality raw sugar in the factories will likely continue. Relatively few studies have been conducted on storage of VHP (very high pol) and VLC (very low color) sugars, especially when the storage period approaches 9–10 months. Monitoring of commercial sugar shipments indicated that, after an initial relatively safe period of storage, sugar color might double or even triple in a short period of time. Large experimental piles of VHP and VLC sugar were monitored in two sugar factories with different crystallization sequences (conventional and double magma) for two consecutive seasons. Temperature and relative humidity probes were placed up to 15 m inside the piles. Samples were taken periodically to evaluate the effects of storage conditions on color, purity, invert sugar content and other parameters. It was concluded that sugar of high quality stores better compared to conventional sugar. However, even VHP sugar can double its color during long-term storage. Sampling near the surface of the sugar pile (up to 1.5 m inside the pile) is not representative of the bulk of sugar. It has been found that sugar temperature follows the ambient trend as deep as 3 m inside the pile. Sugar within 1.5 m of the surface that was not subjected to temperature increase stored well compared to sugar in the core of the pile. It is unclear what conditions trigger color increase in storage. Changes in temperature profiles of raw sugar during storage in commercial warehouses indicate that some exothermic reactions take place in the core of the piles that result in color increase and reduction of sucrose content. The reactions take place even when the initial sugar water content and temperature meet the requirements accepted for safe storage (safety factor below 0.25 and temperature below 30 °C). Lower sugar pH value may be one of the reasons that make sugar less stable in storage. Options of cooling sugar before or during the storage will be considered in future research.