From hardening of marshmallow to graining of hard candies, moisture plays a critical role in determining the quality and shelf life of sugar-based confections. Water is important during the manufacturing of confections, is an important factor in governing texture, and is often the limiting parameter during storage that controls shelf life. Thus, an understanding of water relations in confections is critical to controlling quality. Water content, which is controlled during candy manufacturing through an understanding of boiling point elevation, is one of the most important parameters that governs the texture of candies. For example, the texture of caramel progresses from soft and runny to hard and brittle as the moisture content decreases. However, knowledge of water content by itself is insufficient to controlling stability and shelf life. Understanding water activity, or the ratio of vapor pressures, is necessary to control shelf life. A difference in water activity, either between candy and air or between two domains within the candy, is the driving force for moisture migration in confections. When the difference in water activity is large, moisture migration is rapid, although the rate of moisture migration depends on the nature of resistances to water diffusion. Barrier packaging films protect the candy from air whereas edible films inhibit moisture migration between different moisture domains within a confection. More recently, the concept of glass transition, or the polymer science approach, has supplemented water activity as a critical parameter related to candy stability. Confections with low moisture content, such as hard candy, cotton candy, and some caramels and toffees, may contain sugars in the amorphous or glassy state. As long as these products remain below their glass transition temperature, they remain stable for very long times. However, certain glassy sugars tend to be hygroscopic, rapidly picking up moisture from the air, which causes significant changes that lead to the end of shelf life. These products need to be protected from moisture uptake during storage. This review summarizes the concepts of water content, water activity, and glass transition and documents their importance to quality and shelf life of confections.

When two emulsion drops begin to coalesce, their complete fusion into a single spherical drop can sometimes be arrested in an intermediate shape if a rheological resistance offsets the Laplace pressure driving force. Arrested coalescence of droplets is important, both for its broad impact on commercial food production as well as its potential for fabricating novel anisotropic colloidal microstructures. We use a micromanipulation technique to demonstrate the dynamics of arrested coalescence between droplets with interfacially adsorbed colloids. Surface coverage of the droplets is precisely determined by a capillary aspiration technique and then their coalescence is studied in situ. Depending on their surface coverage, droplets can experience total coalescence, arrested coalescence or total stability. We use microscopic observations along with geometrical packing arguments to confirm that coalescence is arrested due to close-packed jamming of particles. The anisotropic Laplace stress within the arrested structure is balanced by the elastic modulus of the jammed interface and thus further relaxation of the arrested structure is halted. Precise mapping of the arrested coalescence regime at a microscopic scale helps us to anticipate its effects on bulk scale production of such anisotropic colloidal structures.

It has been said that the key to making high-quality candy is understanding and controlling the transitions of sugar. Whether found as crystal, glass, or fluid solution, sugars impart the texture necessary to distinguish one confection from another and to provide a unique experience to the consumer. In principle, the phase/state transitions of sugars are best understood through careful application of the phase diagram. However, many, if not all, confections are not at equilibrium, meaning that the phase diagram is simply a starting point for understanding and controlling the state of sugars. An understanding of the thermodynamic driving forces that push a confection towards equilibrium and the kinetic constraints that control the rate of approaching that equilibrium are key elements to creating products with the desired texture, quality, and shelf life. In this review, we summarize the thermodynamic and kinetic aspects of controlling phase/state transitions in sweeteners, with particular emphasis on applications to confectionery products.

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