Ever wondered why some sweets are called hard boiled. It's all to do with water content
Most sweets are made from a syrup made with sugar and water, or in the case of sugar free sweets, an isomalt syrup or other sweetener.
As the syrup is heated the water content goes down and the consistency of the mixture changes. The longer the syrup is heated. the more water is lost as it changes to steam and the temperature of the remaining syrup rises.
The most accurate way to judge the state of the syrup id to use a thermometer designed to the temperature reached. Modern digital devices give the exact temperature.
Older conventional ones had markings such as "hard crack" or "hard ball", These terms relate to the way confectioners worked without using a thermometer.
If you drop a small amount of the hot syrup into cold water to cool you can judge the temperature of the syrup by the way it behaves. Unboiled syrup will just .disappear into the solution but once the temperature has started to rise you can see it that it remains as a sugary ball that can be felt between the fingers. The texture of the ball indicates the temperature reached.
The first stage is "thread", a sticky mass that can be pulled out between finger and thumb. At 115C it forms a "soft ball" and the syrup will be perfect for soft sweets like fudge. If it's marshmallows you are making you heat a bit more to 120C and you get a "hard ball" when you test it. For boiled sweets and lollipops the syrup needs to be heated to "hard crack" where it makes crisp pieces that break easily and at this stage the temperature will be about 148C.
At even higher temperatures, the sugar starts to go brown and turns to caramel , getting browner and browner till it finally turns black and decomposes at 210C - this point it will also ruin your saucepan! !
If you are tempted to try cooking sugar syup at home, remember it is very hot and can cause nasty burns.
Sugar free sweets
The sweeteners in sugar free sweets do behave differently and i now from talking to the manufactures that say isomalt meeds a higher tempute to get to the hard crack stage.