Sugar gives toffee its sweetness and contributes to its hardness. Sucrose itself does not contribute to Maillard browning, and toffee never reaches a temperature sufficient to caramelize sucrose, so other than a small quantity that may be inverted during cooking, sugar does not significantly add to the caramelized flavor of toffee.
Glucose syrup is a key ingredient in toffee production. As usual, glucose syrup acts as a doctoring agent, helping prevent crystallization of the supersaturated sugar solution. Without the addition of glucose syrup, toffee and caramels would recrystallize rapidly, resulting in a greatly shortened shelf life. Glucose syrup also provides a source of the reducing sugars necessary for Maillard browning. All the caramel flavor found in caramels is a result of Maillard browning. In fact, the candies might more accurately be called “Maillards.” Glucose syrup also contributes greatly to the chewy texture of caramels. Insufficient use of glucose syrup or the use of a high-conversion glucose syrup results in caramels with a short texture instead of the characteristic chew.