The Manufacturing Confectioner • January 2012 79

➤

At first glance, sugar-water state dia-grams can appear rather complex

and far from being a practical tool forunderstanding and improving confec-tionery products. However, over the lastseveral years, these diagrams have beeninstrumental in building a bridge betweenthe art and the science of candymaking.The purpose of this article is to illustratethe usefulness of the sucrose-water statediagram as a map for understanding andpredicting the behavior of sucrose aloneand in sucrose-containing systems. We willjourney around the sucrose-water statediagram exploring processes, such as hardcandy cooking, stopping at specific pointsof interest, such as the melting temperatureof sucrose, and examining differences inwater-solid interactions between crystallineand amorphous states.

SUCROSE-WATER STATE DIAGRAMIn its simplest form, the two-dimensionalsucrose-water state diagram1 is composedof four main curves (Figure 1): the equi-librium freezing (or melting) curve, theequilibrium vaporization (or boiling) curve,

the equilibrium saturation solubility curveand the glass transition curve. The equilib-rium freezing and vaporization curves arealso known as the freezing point depres-sion and boiling-point elevation curves,respectively. This two-dimensional plotshows the physical state of sucrose as afunction of temperature and sucrose con-centration. The two other possible statediagram dimensions, pressure and time,are often excluded from the diagram,assuming that pressure is constant andomitting time-dependence aspects. Sucroseconcentration can be plotted as the dis-solved, solution or liquid-phase concentra-tion (g dissolved sucrose/100g solution) orthe total amount of sucrose present (g dis-solved and g crystalline sucrose/100g total).Most often, and most appropriately, the

Exploring the Sucrose-Water State DiagramThe sucrose-water state diagram is a useful map for understanding and predicting the behavior of sucrose.

Shelly J. Schmidt, PhDUniversity of Illinois at Urbana-Champaign

Shelly Schmidt hasbeen a faculty mem-ber at the Universityof Illinois in thedepartments of foodscience and humannutrition and agricul-tural and biologicalengineering since1986.

1 The term state diagram is used herein, since, strictly speaking,a state diagram includes both equilibrium (e.g., freezing, vapor-ization and solubility) and nonequilibrium (e.g., the glass tran-sition) events in a single figure; whereas, a phase diagramshould contain only equilibrium events. The term supplementalphase diagram is also used. Figure 1

Sucrose-water State Diagram