The most accurate way to measure the temperature of cooking sugar syrup is to use a thermometer; there is little reason that a home confectioner would want to use any other method. Finger testing is a time-honored technique that can be used in place of, or in addition to, a thermometer: dipping fingers in ice water, quickly retrieving a sample of hot syrup from the boiling pot with your cold, damp fingers, and immediately placing your fingers, with the hot syrup, in the ice water before you burn them. While professionals frequently use their bare fingers and ice water to check the temperature of cooking sugar, this technique is best not attempted by nonprofessionals.
A similar technique can be used at home using a teaspoon.
- Place a small bowl of ice water next to the saucepan of cooking sugar.
- As the sugar boils, spoon small samples of the syrup out of the saucepan and immerse
- the spoon holding the syrup in the ice water.
- Allow the syrup to cool for several seconds, then remove the spoon from the water.
- Take the cooled sample of syrup between your thumb and forefinger and squeeze it to
- evaluate the consistency.
The temperature of the cooking sugar corresponds with the stages of sugar cooking as illustrated in the photographs below.
While this test is reasonably accurate in the hands of an experienced sugar cook, nothing beats the accuracy of a thermometer for achieving excellent results batch after batch. Perhaps the only time manually testing a batch of sugar is really useful is when cooking Soft Caramels. By spoon testing the cooking caramels, it is easier to be certain that the finished candies will have the right texture.
