Much of the art of confectionery is based on the science of crystallization. In the case of hard candy, toffee, brittle, and caramels, the object is to prevent crystallization in order to create the organic “glass” that is the defining quality of these products. Table sugar (sucrose) is crystalline in nature, and, unless steps are taken to prevent it, sucrose reverts to a crystalline state. Understanding and controlling crystallization is the basis of the entire field of confectionery. Therefore, it is important for the professional to have a basic comprehension of the crystallization process and how to control it. Fortunately, no advanced degree in physics or chemistry is required in order to grasp the fundamentals of sugar crystallization. Once a professional understands the key concepts, he or she can manipulate the formulas and procedures to get precisely the desired results. The following sugar-cooking procedure illustrates the principles involved. Each of the steps is designed to help prevent crystallization.
Technique Theory: Standard Wet-Sugar Cooking
Knowing the simple procedures of the standard wet-sugar cooking method—and having an understanding of the basic theory behind each of those procedures—is invaluable to the confectioner and will help him or her succeed consistently in sugar confectionery. Two simple goals are at the heart of sugar cooking: the sugar must first be dissolved, and then the desired amount of water must be removed. Each of the following steps helps to prevent recrystallization of the sugar.
IN A POT OR CANDY KETTLE, COMBINE SUGAR WITH 20 PERCENT OR MORE WATER TO MAKE THE SUGAR THE TEXTURE OF WET SAND. The water in this procedure is the solvent: it is the substance into which the sugar dissolves. Without the water, the sugar could not go from a crystalline state to an amorphous, or noncrystalline, state. The precise amount of water used is not critical, provided it is sufficient to dissolve the sugar fully. Twenty percent is a satisfactory amount. At the boiling point, sugar solutions can dissolve approxim-ately 80 percent sugar. So, when the 20 percent solution is heated to boiling, it is certain that all of the sugar will dissolve. Using more water will not generally be harmful to the finished product, but, since the goal of sugar cooking is to remove the desired amount of water, the cooking time will be increased by using a greater percentage of water. (See Sugar Cooking.)
PLACE THE POT ON THE HIGHEST POSSIBLE HEAT WITHOUT THE FLAME COMING UP THE SIDES. Sugar should always be cooked on the highest possible heat. There are two primary reasons for this: to minimize unwanted browning and to prevent crystallization. Sugar cooked to a high temperature, as when making hard candy, browns more when it is cooked slowly than when it is cooked quickly. The browning not only affects the candy’s color but also brings with it caramel flavor notes that are often not welcome. The more quickly the sugar reaches the terminal temperature, the less browning occurs. Cooking a sugar solution rapidly helps to prevent crystallization by putting more energy into the system, making the sugar solution less likely to revert to a crystalline state. These two factors are the reasons why, in confectionery shops, syrups are cooked in copper kettles on powerful candy stoves. The copper conducts heat extremely well, and the rounded bottom of the kettle provides a large surface area for heating, resulting in a fast cook. The stoves in confectionery shops are fitted to accept the kettles for the most efficient transfer of heat into the syrup.
STIR CONSTANTLY WITH A WOODEN SPOON UNTIL THE SOLUTION COMES TO A BOIL. Stirring a syrup as it comes to a boil helps to ensure that the sugar crystals circulate throughout the syrup, dissolving quickly and completely. Any undissolved sugar crystals remaining in the solution act as seeds, or nuclei, forming more sugar crystals, which themselves then initiate further crystallization. Confectioners traditionally use wooden paddles or spoons for stirring, as metal conducts heat away from the solution, resulting in cool spots in the syrup that are more prone to crystallization.
WHEN THE SOLUTION REACHES A BOIL, STOP STIRRING. Stirring—as beneficial as it is to the syrup during heating—becomes detrimental once the solution begins to boil. Stirring, or any other agitation, of a supersaturated solution can initiate crystallization by causing the sugar molecules to collide and bond together to form crystals. (See sugar crystallization diagrams.) The exception to this rule applies when the solution contains a dairy product or another type of ingredient that will burn if not stirred during cooking. In formulas containing such ingredients, allowances are made for this excess agitation in the form of extra doctoring agents.
REMOVE IMPURITIES FROM THE TOP OF THE SOLUTION. When syrup first reaches a boil, gray foam often coalesces on the surface of the sugar. This foam can be caused by traces of mineral salts left in the sugar from the refining process or by any other impurities that may be present in the syrup. These impurities should be removed in order to improve the appearance of the finished product and to prevent the impurities from becoming seeds on which sugar crystals can form. The quantity of impurities in the sugar depends on the refining and storage of that sugar and may range from being virtually nonexistent to covering the entire top of the syrup.
ADD A DOCTORING AGENT TO THE SOLUTION. In confectionery, doctoring agents—also called “doctors”—are ingredients added to help prevent or control the crystallization of sugar. Three categories of doctoring agents are typically used in candy making: glucose syrups, acids, and invert sugar. While all of them help to control crystallization, each has its own characteristic effects on the final product.
GLUCOSE SYRUPS. Glucose syrup is ubiquitous as a doctoring agent throughout confectionery. Glucose syrups with different dextrose equivalents (DEs) affect the finished product slightly differently with regard to texture, flavor release, and hygroscopicity. When using glucose syrup as a doctoring agent, add it after the solution reaches a boil, as it is easier for the sugar to fully dissolve in the water without the presence of the syrup. Low-DE syrups contribute to a chewy texture and less sweetness. Higher-DE syrups result in a shorter texture and greater levels of sweetness. (See Characteristics of Glucose Syrups.)
ORGANIC ACIDS. Tartaric acid, cream of tartar, lemon juice, and vinegar are also commonly used as doctoring agents in sugar cooking. These ingredients work by inverting a portion of the sugar in the syrup. (See Inversion.) In addition to preventing crystallization, inversion makes the finished product softer, sweeter, shorter textured, more hygroscopic, and more prone to browning. Inversion is an ongoing process; as long as the sugar and acid are together in a fluid state, inversion will continue, resulting in a softer, stickier, and potentially browner finished product. In most cases these are qualities to be avoided. This is the reason some candy formulas specify the temperature at which to add the acid used as a doctoring agent.
INVERT SUGAR. Invert sugar may be added to syrups directly. By adding invert sugar directly, rather than relying on acids to invert a portion of the sugar, the confectioner can get more consistent results that are not affected by variables such as the output of the stove, the strength of acids, or the hardness and pH of water. Regardless of whether invert sugar is a discrete ingredient or is created by inversion during cooking, it has the same tendency to increase sweetness, provide rapid flavor release, increase hygroscopicity, and contribute to potential Maillard browning. (See Maillard Reaction.)
USING A MOISTENED PASTRY BRUSH, WASH DOWN THE SIDES OF THE SUGAR POT TO REMOVE ANY SUGAR RESIDUE. Repeat this step as often as necessary to keep the sides of the pot clean, but do not clean more often than necessary. Brushing the sides of the sugar pot with a wet brush removes the sugar crystals that are likely to form there and returns them to the solution. If such crystals are allowed to remain undissolved on the sides of the pot, they are likely to make their way back into the mixture after cooking, seeding it and initiating crystallization. Unless these crystals become part of the solution, they quickly become part of the problem! Remember that the goal when cooking sugar is to remove water from the syrup. Therefore it is counterproductive to wash the sides of the pot excessively, as this simply introduces more water that must again be removed. Clean the side of the pot only when there is sugar present on it.
INSERT A THERMOMETER INTO THE SOLUTION AND COOK TO THE DESIRED TEMPERATURE. Alternatively, use a refractometer or a finger test to measure the concentration of sugar in the solution. Various methods exist for determining the percentage of water and sugar present in a cooking solution. The most common method is to use a thermometer and to cook the syrup to a predetermined temperature. At standard atmospheric conditions, sugar cooked to a given temperature will always contain the same percentage of dissolved solids. The following graph indicates the relationship between the temperature to which the sugar is cooked and the resulting dissolved-solids content. The thermometer is the most accessible, reliable method for determining the sugar density of a cooking mixture. Another highly accurate method is the use of a refractometer. Available in a variety of ranges, a refractometer quickly and accurately measures the density of a syrup without the fluctuations due to atmospheric pressure, altitude, and relative humidity that are inherent with a thermometer. Another time-honored method is to test the mixture using a bowl of ice water and one’s fingers. (See Stages of Sugar Cooking.) The finger test, while adequate for some purposes, and having enjoyed many years of use by confectioners, is subjective and dependent on the experience and skill of the confectioner. More consistent, accurate results are obtained by using either a thermometer or refractometer.
Theory: Boiling Point of Cooking Syrup
It is a common occurrence that the temperature of the boiling syrup remain at or below approximately 106°C/223°F for quite some time before it begins to steadily rise. Why does the temperature of cooking syrup climb so slowly at first and then much more rapidly? When the syrup reaches 106°C/223°F, the solution becomes saturated, and the temperature rises more rapidly, actually accelerating as it cooks. If 1 kilogram/2.2 pounds of sugar were combined with 200 grams/7 ounces of water and cooked, it would quickly reach 106°C/223°F (saturation) and would continue cooking relatively quickly beyond that temperature. If the same kilogram of sugar were combined with a kilogram of water, the syrup would take much longer to become saturated. Once it reached 106°C/223°F, however, that sugar would cook just as quickly as the batch that began with less water. All the extra cooking time for the batch of sugar with the kilogram of water would have been spent removing water to reach the point of saturation. Once saturation is reached, the syrups would cook at the same rate. This is the reason the confectioner uses a minimum of water to dissolve sugar for cooking, so as not to waste time waiting for a syrup to reach saturation and for the temperature to rise.
The higher the sugar content of a syrup, the higher its boiling temperature is. Pure water boils at 100°C/212°F; an 80-percent sugar solution boils at 110°C/230°F. When the solution reaches 98 percent sugar, the boiling point is raised to 155°C/311°F. Early in cooking, a large amount of water is present in the syrup; much of this water must be removed in order to noticeably increase the percentage of sugar and therefore raise the boiling point. It takes time to remove this water. Later in cooking, a smaller amount of water remains in the syrup; as a result, removing less water brings about a larger corresponding increase in the percentage of sugar and in the boiling point. Therefore, the boiling point rises quickly. The less water that remains in the syrup, the more quickly the sugar percentage increases, and the faster the temperature rises.
Technique Theory: Standard Dry-Sugar Cooking
The important difference between the standard wet-sugar cooking technique and the dry technique is that the dry technique is used only for making caramel, while the wet technique can be used to make a variety of syrups, from thread stage to hard crack or caramel. The key reason for this difference is the use of water as a solvent. When cooking sugar by the wet method, the sugar is dissolved in water, then a portion of the water is removed. In the dry method, the sugar is not dissolved, but rather is melted. Because no water is added, the only possible outcome of the dry method is melted, caramelized sugar.
PRIOR TO CARAMELIZING, WORK A SMALL AMOUNT OF LEMON JUICE OR OTHER DOCTORING AGENT INTO THE SUGAR. As always when cooking sugar, the addition of acid inverts some of the sugar, preventing crystallization and softening the finished product. In the dry method the acid also helps to prevent the formation of agglomerates of sugar as the sugar melts. Again, many formulas provide specific information as to the amount and type of acid to use. Excessive acid softens the finished product. As a rule, only a few drops per pound of sugar are required to help prevent crystallization and to prevent lumps from forming.
PLACE THE SUGAR IN A HEAVY-BOTTOMED SUGAR POT OR SAUCEPAN. Place the pot on high heat, stirring the sugar constantly with a wooden spoon to ensure that the sugar heats evenly. The sugar may either be placed in the pot all at once or added in stages, with the confectioner allowing each addition of sugar to melt fully before adding the next. Each of these methods has its merits. When the amount of sugar being caramelized is small, it is easiest to put all of the sugar in the pot, place the pot on direct heat, and caramelize the sugar. If the amount of sugar is larger, it is more efficient to add the sugar in stages, which eliminates the need to stir the entire quantity of sugar as it heats. Both variations on the method proceed more quickly if the pot is preheated. Regardless of which technique is employed, constant stirring is required in order to heat and melt the sugar evenly without forming lumps. This amount of stirring is contraindicated for the wet method, in which stirring initiates crystallization of the dissolved sugar. There the sugar is dissolved in water, and the desired result is to maintain the sugar’s amorphous form while removing water. In the dry method, however, the sugar is already in crystalline form, and the desired outcome is to melt the crystals. When making caramel by either method, a wooden spoon is the preferred implement for stirring because it conducts little heat.
CONTINUE STIRRING THE SUGAR OVER HIGH HEAT UNTIL IT IS COMPLETELY MELTED AND CARAMELIZED TO THE DESIRED DEGREE. The dry method is used exclusively to caramelize sugar. It is not possible with the dry method to reach intermediate stages of sugar cookery such as thread, soft ball, and so on because there is no water present. The degree of caramelization desired depends on the product being made; deeper caramel color and flavor are more desirable for some products than for others. The darker the color of the caramel, the more bitter the caramel flavor carried into the finished product will be. This may or may not be desirable, depending on the intended use of the caramel and the flavor sought.