If I leave my jar of brown sugar standing overnight, the surface crystals will bind together and I will need a spoon to scrape and loosen them so I can pour the sugar out. What property of brown sugar causes the surface to bind together so quickly?
鈥� This question was really nostalgic for me. Many years ago I collaborated with David Bagster, a chemical engineer at the University of Sydney, whose research career was dedicated to the wayward properties of unrefined sugar and how to overcome them to allow it to be handled in bulk.
Raw or brown sugar crystals have a permanent liquid layer on their surface. Normally this is apparent only as an obvious stickiness but if it can evaporate, as in your correspondent鈥檚 sugar jar, the sugar in the surface layer will crystallise and cement the grains together. In cold weather the sugar can crystallise throughout the whole mass, turning it solid.
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Bagster told me of a spectacular case of this, in which a bulk transport ship took on a load of raw sugar in the tropics destined for a cold-water Russian port. On arrival the sugar had set like rock and was immovable. The last I heard, the situation hadn鈥檛 been resolved and the ship was still clinging on to its load.
Guy Cox, Australian Centre for Microscopy and Microanalysis, University of Sydney
鈥� If the humidity around brown sugar is low then it will dry and clump into hard pieces, making it difficult to pour. This happens to my brown sugar even in a jar with a lid.
To prevent this, during the winter months I put a piece of bread or apple peel into the container. The sugar then stays moist and free from clumping.
Gina Kirby, New Maryland, New Brunswick, Canada
