Understanding Sugar-Boiling
from Making Chocolates by Alec Leaver

The basis for making candies is sugar and water, therefore it is necessary to understand how they behave. For instance fudge and caramels are made from similar ingredients, but fudge has a crystalline texture and caramels do not, so it is important to know how to achieve this. For instance, caramels are a mixture of sugar, water, and fat. Milk solids are normally added for flavor and other additions may include nuts, dried fruit and flavorings. Fudge is simply a caramel encouraged to grain. Fudge is also cooked to a lower temperature than caramel. This gives a softer, more moist result.

Approximately 15 oz. of granulated sugar can be dissolved in 1/2 pint of cold water. Hot water, however, can hold a much greater quantity of sugar, and 1/2 pint of boiling water can dissolve as much as 2 1/2 pounds of granulated sugar. At this point no more sugar can be dissoved and it is known as a "super-saturated" solution. If more sugar were to be added, it would just remain in crystal form no matter how much stirring you did.

Conversely, a super-saturated solution of sugar which is then cooled can no longer hold all its sugar, which then begins to fall out of solution into crystals resembling dry sugar again. This tendency of sugar solutions to crysallise, or grain, is of great importance in sugar confectionary. Professional sugar boilers know exactly how graining can be controlled, and how it can be encouraged to produce different kinds of sweets.

The most usual way of controlling grain is by adding what is called a doctor to the sugar solution. There is a large range of doctors that are used in various strengths depending upon the desired result. There are broadly two types of doctor, sugar substances which do not crystallise readily and acids or acid substances (acetic acid found in vinegar, citric acid found in citrus fruits, or tartaric acid from grapes. Cream of tartar, an acid substance, is also often used. These must be added in very small quantities.

The most widely used doctor is one of the sugar substances, corn syrup being one, and is added in fairly large amounts.

It is also necessary to know how to encourage grain, particulary for making fudge and fondant. A smaller portion of the doctor is used, but a certain amount is essential or the result will be very coarse crystals instead of a soft, smooth texture.

There are two methods of encouraging grain; agitation and seeding. Seeding consists of introducing some crystalline substance into the boil at the end of the cooking process. This substance may be icing sugar, fondant or anything with a similar structure. Grain by agitation can be caused by stirring or beating the mixture while in the pan, rubbbing the back of spoon on the side of the pan until a small quantity begins to cloud, or pouring the mixture out on to a slab and stirring or folding.

The syrup will thicken and become opaque quite quickly; moreover, the crystals of the finished product will resemble those which were added, so that, if icing sugar were added, the result would be a fine-grained fudge, but if sugar were added, it would be very coarse.

The degree of hardness of toffees and caramels depends entirely on their water content. A soft caramel or fudge contains more water than a hard toffee such as reacle toffee, whic is itself softer and contains more water than butterscotch.

There is a direct relationship between the amount of water left in a boiled syrup and the temperature of the syrup. Thus we can draw up a table which compares the hardness of various sweets with their final cooking temperatures (hard crack, soft crack, hard ball, soft ball, etc.)

If a syrup should accidently reach a temperature higher than you intended, you can always add a little boiling water (cold water would make it explode) and continue cooking until you reach the correct temperature. Any sweet can be recooked in this way exept nougats or marshmallows.

Flavorings can thin a boiling syrup, and if you keep boiling to get the syrup back up, the flavor usually boils away. One of the methods of solving this problem is to cook the syrup beyond the final temperature, so it is thicker than necessary, then cool it until the flavor can be added, thus thinning the syrup to the correct consistency.