Description
Presenter: Richard W. Hartel, PhD, Renee Lietha, Rajesh Bund, Baomin Liang and Lian Yu, University of Wisconsin – Madison
Stickiness and graining are common problems associated with high humidity during storage of hard candies. Although the molecules in the glassy structure of a hard candy are tightly packed, the random nature of the molecular organization means there are spaces between the sugar molecules — the free volume — into which smaller molecules like water can diffuse. Water molecules from the air slowly penetrate into this free volume between sugar molecules in the hard candy glass, plasticizing the matrix as the water content increases. Since penetration of the water molecules into the glassy matrix is slow compared to sorption of water molecules at the air surface of the candy, a backlog of water molecules builds up at the surface. This causes formation of a distinct moisture front, which slowly penetrates into the candy, leaving behind a layer of higher water content that becomes sticky and potentially can crystallize.
