Boil sugar and water and something remarkable happens: as water boils off, the syrup's temperature climbs steadily, and each temperature makes a different candy.
Key idea
Sugar stages (at sea level, from the Exploratorium): thread 230°F to 235°F; soft ball 235°F to 240°F (fudge, fondant); firm ball 245°F to 250°F (caramels); hard ball 250°F to 265°F (nougat, marshmallows); soft crack 270°F to 290°F (taffy, butterscotch); hard crack 300°F to 310°F (lollipops, brittle, spun sugar); then caramel, from clear liquid near 320°F to brown near 338°F, and burnt by about 350°F. At high altitude, subtract about 1°F for every 500 feet.
Why it works
The temperature of a sugar syrup tells you how concentrated it is. The less water left, the higher the boiling point and the harder the candy when it cools.
Worked example: Altitude
A caramel recipe says firm ball, 248°F. You live at 5,000 feet. What temperature?
- $5000 \div 500 = 10$, so 10°F lower.
- $248 - 10 = 238$.
Answer: About 238°F.
Safety
- Cooked sugar is far hotter than boiling water and sticks to skin. Use a heavy, deep pan, long-handled tools and an accurate candy thermometer, and keep children and pets well away.
- Add cream or butter to hot caramel slowly and stand back; it bubbles up hard.
Common mistake
Stirring a syrup that has started to crystallize, or splashing syrup on the sides of the pan. Brush the sides with a wet pastry brush and swirl instead of stirring.
Practice at home
- Check your candy thermometer in boiling water first: at sea level it should read 212°F (lower at altitude).
- Make caramel sauce: cook sugar to amber, then whisk in warm cream off the heat.
In Meal Prep
- Marshmallows: a hot sugar syrup whipped into gelatin
- Simple syrup: the gentlest sugar cooking
The science behind it
- Boiling point elevation: why a syrup boils hotter as it concentrates