4. Get it Down to a Science
The process of turning sugar into a hard, smooth, transparent confection involves heating a sugar/corn syrup/water solution to 300 – 310° F. {150 - 155° C.}, or what is known as the hard crack stage of sugar. The use of a candy thermometer is not essential, but highly recommended and accuracy is critical.
Test a thermometer’s accuracy by inserting it in a pan boiling water. After about five minutes, it should read 212° F or 100° C. If the reading is higher or lower, take the difference into account when testing the temperature of your sugar syrup.
For granulated sugar to transform into sugar glass (yes, hard candy is technically a glass) the sugar/corn syrup mixture needs to be heated to the proper temperature and cooled properly. If uncooked sugar crystals are reintroduced to the candy syrup, the mixture will revert back to its original large crystal state!
To prevent this, after your mixture comes to a boil, wash down the sides of the pan with a wet pastry brush to wash away any sugar granules clinging to the sides of the pan. Also, use only clean, dry utensils when stirring the sugar syrup.
