Although technically cooking to the thread stage does not create a candy (but instead a syrup), this cooking stage is still considered a part of the candy-making process. Basically, making candy is boiling sugar in water, which, as we know, is what creates a syrup. What dictates which type of candy you are making is the point when the water stops boiling.
There are seven stages of candy making: thread, soft-ball, firm-ball, hard-ball, soft-crack, hard-crack, and caramel. Different types of candy—from fudge to lollipops—need to be cooked to different stages. As the water boils, the higher the temperature and greater concentration of sugar, creating very different types of confections. Since the thread stage is at the lowest temperature range, the water is boiling for the shortest amount of time, not allowing the sugar to come together and keeping it in a liquid form.
Tools to Determine Each Stage
A candy thermometer is a necessary tool for making candy at home. Each stage occurs at a different range of temperatures, so keeping an eye on the thermometer will help you know when the sugar has reached the correct stage. If you don't have a candy thermometer, or would like to use an additional technique, you can try the cold water method. Each stage can be determined by what the syrup's consistency is when dropped into cold water.
If you are using a candy thermometer and live in a higher altitude, you will need to do a bit of calculating: for every 500 feet above sea level, subtract one degree Fahrenheit from the stage's required temperature.
The Thread Stage
The thread stage occurs between 223 and 235 F, the lowest temperature range in candy making. In addition to using a candy thermometer, you can determine the thread stage by dropping a spoonful of the hot syrup into a bowl of very cold water. If the syrup drips from a spoon and forms thin threads in cold water (kind of resembling a spider's web), the thread stage has been reached. If it is still a liquid then it needs to be cooked to a higher temperature; if the syrup can be gathered into a ball when using your fingers, then it was overcooked to the soft-ball stage.
Thread Stage Sweets
You will need to achieve the thread stage if you plan to make syrups, some icings, and fruit liqueurs.