Confectionery is the most temperature-sensitive cooking most people attempt. The difference between a soft caramel and a hard one is a few degrees, and there is no way to judge it by appearance until it is too late to change.
What Is Happening
Boiling a sugar syrup drives off water. As water leaves, the sugar concentration rises and so does the boiling point, which means temperature is a direct proxy for how much water remains.
That relationship is why every confectionery recipe specifies a temperature rather than a time. The temperature tells you the concentration, and the concentration determines the texture once it cools.
A reliable probe thermometer is therefore not optional equipment for this kind of work, and ranges listing instant-read and probe models alongside scales, such as Escali, cover both the weighing and the temperature measurement that sugar work requires.
The Classic Stages
- Thread, around 106 to 112°C: syrups and some icings
- Soft ball, around 112 to 116°C: fudge, fondant, Italian meringue
- Firm ball, around 118 to 120°C: soft caramels
- Hard ball, around 121 to 130°C: nougat, marshmallow
- Soft crack, around 132 to 143°C: taffy and butterscotch
- Hard crack, around 149 to 154°C: brittle, toffee, spun sugar
The old cold water test, dropping syrup into water and judging the ball it forms, is what the names describe. It works and is considerably less precise than a thermometer.
Caramel
Beyond the hard crack stage, sugar begins to caramelise, browning and developing flavour from around 160 degrees. Light caramel sits around 170; dark caramel around 180; above that it burns rapidly and turns acrid.
The window is narrow and the process accelerates, which is why caramel goes from perfect to burnt in seconds. Removing the pan from the heat slightly early and letting residual heat finish the job is the safer approach.
Practical Points
Use a heavy pan, since thin bases produce hot spots that burn the sugar locally. Do not stir once the sugar has dissolved, as agitation encourages crystallisation.
Brush down the sides of the pan with a wet brush to dissolve stray crystals, which otherwise seed crystallisation throughout the batch. A little acid, lemon juice or cream of tartar, or a spoon of glucose, helps prevent it.
Altitude
Water boils at a lower temperature at altitude, which shifts every one of these figures downward. The usual rule of thumb is to subtract roughly half a degree for every hundred metres above sea level.
Anyone working significantly above sea level should adjust rather than following recipes literally.
Safety
Sugar syrup at hard crack stage is above 150 degrees and sticks to skin, which makes it considerably more dangerous than boiling water. It causes serious burns.
Work with sleeves down, keep children and pets out of the kitchen, never move a pan of hot sugar unnecessarily, and have a bowl of cold water within reach. Adding cream or butter to hot caramel causes violent bubbling; add it slowly and off the heat.