The Science Of Sugar Confectionery

Rock candy has a unique texture. It is made of large chunks of flavored sugar that you can crunch in your mouth. Other candies come in a variety of textures: chewy (fudge), gritty (cotton candy), or hard (glass candy).

The science of sugar confectionery

To make most types of candies, you always start by dissolving sugar in boiling water. This forms a sugar syrup, which you can cool down by taking it off the burner. But how you cool down the syrup can make all the difference.

For instance, if you want to make rock candy, you need to let the syrup slowly cool down over many days until big sugar crystals form. But if you want to produce fudge, you need to continuously stir the syrup after an initial cooling period, so when the sugar crystals form, they stay small and do not grow too much. If you want to make cotton candy and glass candy, you need to cool the syrup quickly to keep crystals from forming.

The main difference between these different types of candies is whether sugar crystals form and, if so, what their size is. So how do sugar crystals form, and what causes them to have different sizes when the syrup is cooled down?

When you add granulated sugar to water, some of the sucrose molecules start separating from one another because they are attracted to the water molecules (Fig. 3). When water and sucrose molecules are close to each other, they interact through intermolecular forces that are similar to the intermolecular forces between sucrose molecules.

Figure 3. When granulated sugar is added to water, it breaks apart because the water molecules are attracted to the sucrose molecules through intermolecular forces. As a result, each sucrose molecule is surrounded by water molecules and is carried off into the solution.

Figure 4. When a sugar crystal is added to a cup of water, some sucrose molecules separate from the crystal while others join the crystal. Whether the crystal dissolves in water or grows in size is determined by comparing the relative number of sucrose molecules dissolving and leaving the crystal with the number of sucrose molecules leaving the solution and joining the crystal.

As we add more granulated sugar to the solution, the rate of dissolving decreases and the rate of crystallization increases, so at some point, both rates are equal. In other words, the number of sucrose molecules leaving the crystals is the same as the number of sucrose molecules joining the crystals. This is what happens when the solution is saturated.

As a result, past that point, if we add more sugar crystals, the process of dissolving will continue, but it will be exactly balanced by the process of recrystallization. So the sugar crystals cannot dissolve in the water anymore. In this case, the crystals and the solution are in dynamic equilibrium. This means that the size of the crystals stays the same, even though the sucrose molecules are constantly trading places between the solution and the crystals.

To make rock candy, we initially used more sugar than could dissolve in water at room temperature (three cups of sugar for one cup of water). The only way to get all of that sugar to dissolve is to heat up the water, because increasing the temperature causes more sugar to dissolve in water. In other words, the dynamic equilibrium is affected by a change in temperature. If we increase the temperature, we increase the dissolving process, and if we reduce the temperature, we decrease the dissolving process.

To make glass candy, you cool the sugar syrup so rapidly that no crystals have time to form. The dissolved sucrose molecules start binding with each other, but in no particular order. When this happens, the candy is amorphous, and it is an example of a glass.

Cotton candy is produced a little differently because the process does not start with sugar syrup. First, granulated sugar is heated in a cotton candy machine until it melts and the intermolecular forces between the sucrose molecules are broken. Having liquefied the sugar, the cotton candy machine then sprays the liquid through tiny nozzles so that it forms fine filaments of liquid that solidify immediately.

Consumption of added sugar has significantly increased over the past 50 years, and this rise in consumption coincides with the rise of obesity, type 2 diabetes, and heart disease. So, is added sugar harmful?

Hungry for more? Learn about the Science of Food. --> What is sugar? The white stuff we know as sugar is sucrose, a molecule composed of 12 atoms of carbon, 22 atoms of hydrogen, and 11 atoms of oxygen (C12H22O11). Like all compounds made from these three elements, sugar is a carbohydrate. It’s found naturally in most plants, but especially in sugarcane and sugar beets—hence their names.

When you add sugar to water, the sugar crystals dissolve and the sugar goes into solution. But you can’t dissolve an infinite amount of sugar into a fixed volume of water. When as much sugar has been dissolved into a solution as possible, the solution is said to be saturated.

When you cook up a batch of candy, you cook sugar, water, and various other ingredients to extremely high temperatures. At these high temperatures, the sugar remains in solution, even though much of the water has boiled away. But when the candy is through cooking and begins to cool, there is more sugar in solution than is normally possible. The solution is said to be supersaturated with sugar.

Supersaturation is an unstable state. The sugar molecules will begin to crystallize back into a solid at the least provocation. Stirring or jostling of any kind can cause the sugar to begin crystallizing.

The fact that sugar solidifies into crystals is extremely important in candy making. There are basically two categories of candies - crystalline (candies which contain crystals in their finished form, such as fudge and fondant), and noncrystalline, or amorphous (candies which do not contain crystals, such as lollipops, taffy, and caramels). Recipe ingredients and procedures for noncrystalline candies are specifically designed to prevent the formation of sugar crystals, because they give the resulting candy a grainy texture.

One way to prevent the crystallization of sucrose in candy is to make sure that there are other types of sugar—usually, fructose and glucose—to get in the way. Large crystals of sucrose have a harder time forming when molecules of fructose and glucose are around. Crystals form something like Legos locking together, except that instead of Lego pieces, there are molecules. If some of the molecules are a different size and shape, they won’t fit together, and a crystal doesn’t form.

A simple way to get other types of sugar into the mix is to "invert" the sucrose (the basic white sugar you know well) by adding an acid to the recipe. Acids such as lemon juice or cream of tartar cause sucrose to break up (or invert) into its two simpler components, fructose and glucose. Another way is to add a nonsucrose sugar, such as corn syrup, which is mainly glucose. Some lollipop recipes use as much as 50% corn syrup; this is to prevent sugar crystals from ruining the texture.

Fats in candy serve a similar purpose. Fatty ingredients such as butter help interfere with crystallization—again, by getting in the way of the sucrose molecules that are trying to lock togeter into crystals. Toffee owes its smooth texture and easy breakability to an absence of sugar crystals, thanks to a large amount of butter in the mix.

Explore the super sweet science of sugar by creating sugar skulls, chocolate lollipops, rock candy sticks, gummy gems and sugar glass. Features 23 pieces including a sugar skull mold, candy molds, rock candy sticks and full instructions. You supply the sugar.

The more I explore this notion, the more fascinating I find it and the more I enjoy tapping into those emotions. In other words, the true path to our inner selves may indeed be something as simple as candy. Though confections are tucked beneath the broad umbrella of pastry arts that includes chocolate, ice cream, cakes, and plated desserts, my own interest in candy has increased along with a better understanding of its underlying science. Through candy-making we can explore the properties of sugars and fats, the behavior of concentrated syrups and crystallization, and numerous complex interactions that influence taste and texture.

Controlling crystallization, for example, is very important. Understanding just when to stir a sugar syrup (or when not to) and when to use inhibitors like acids and glucose will help provide the right end result. Simple knowledge of basic hydrocolloids can help us craft a range of textures like chewy gummies, melt-in-your-mouth pâtes de fruits and ultra-light marshmallows.

Navigating the complex flavor-creating mechanisms of caramelization and Maillard reactions help us understand what is happening as our cooked confections transform into something greater than the sum of their parts. My own recent explorations have resulted in tooth-friendly sugar-free candies for a private client and "savory" confections flavored with vegetable juices, such as carrot. With just a little confidence, patience, and know-how, the sky is the limit!

Designed as a complete reference and guide, Confectionery Science and Technology provides personnel in industry with solutions to the problems concerning the manufacture of high-quality confectionery products.

Richard W. Hartel, is Professor of Food Engineering with the Department of Food Science at the University of Wisconsin-Madison. He conducts research on phase transitions in foods, primarily sugar confections, chocolate and ice cream. He teaches courses in Food Manufacturing, Food Preservation, Food Functionality, and Candy Science, as well as a freshman career orientation course. He has been involved with the UW Resident Course in Confectionery Technology (candy school) as an instructor since 1987 and as lead coordinator since 1998. 041b061a72