Sweet glasses
Stories from Physics
for 11-14
14-16
Candy floss and lollipops are technically considered glasses as they are materials which have been cooled to a rigid state without crystallising. The film industry makes use of the similar properties of certain kinds of sugar and glass. Bottles and window panes on movie sets are often made of sugar so the props can display a safe but realistically brittle shattering behaviour when broken.
Sugars change from being soft and rubbery to a hard, brittle material at what is referred to as the glass transition temperature. The transition temperature is dependent on the moisture content of the confectionery. Any water in the air acts as a plasticiser, lowering the transition temperature to room temperature and making the sugar rubbery.
Glassy sweets typically have transition temperatures in the range of 65-70°C whilst the sucrose used to make candy floss has a transition temperature of around 60°C. Sweets with high moisture content, such as jellies, gummies and marshmallows, have transition temperatures as low as -40°C so exist in a soft, amorphous state at room temperature.
References
Sweet Glasses
J. M. Aguilera, Edible Structures: The Basic Science of What We Eat, Boca Raton, CRC Press, 2013, pp. 66-69
A. Paul, The Chemistry of Glasses, London, Chapman and Paul, 1982, p. 1
P. Hull, Glucose Syrups: Technology and Applications, Oxford, Wiley Blackwell, p. 152
R. W. Hartle, & C. M. Nowakowski, Non-equilibrium States in Confectionery, In B. R. Bhandari, & Y. H. Roos (eds.), Non-Equilibrium States and Glass Transitions in Foods: Processing Effects and Product-Specific Implications, Amsterdam, Elsevier, 2017, pp. 283-302.
J. N. Coupland, An Introduction to the Physical Chemistry of Food, New York, Springer, 2014, p. 104
