Sugar syrup stages and temperatures

Sugar stage temperature chart

This chart uses the Celsius ranges published by NIST, the US National Institute of Standards and Technology, with Fahrenheit converted and rounded to the nearest degree. The cold-water tests and typical uses combine NIST and the Exploratorium. All temperatures are for sea level; see adjusting for altitude if you live higher up.

To do the cold-water test, drop a little hot syrup into a bowl of very cold water, gather it with your fingers and feel how it has set. At hard crack, let it cool in the water for a few moments first, because it is hot enough to burn (Exploratorium).

NIST lists Italian meringue under firm ball; for how the hot syrup is beaten into the whites, see French, Swiss and Italian meringue compared. For the colours and flavours above 160 °C (320 °F), see Caramelization explained.

Where published ranges differ

Sugar stages are kitchen conventions, not physical constants, and reference charts draw the boundaries in slightly different places. The biggest gap is at thread stage, where NIST starts at 102 °C (216 °F) and the Exploratorium at 110 °C (230 °F). King Arthur Baking, quoting the professional textbook Baking and Pastry: Mastering the Art and Craft, gives single targets for soft and firm ball and a lower soft-crack range than the other two. At the top, the Exploratorium already calls 177 °C (350 °F) burnt, while NIST runs the caramel stage to 182 °C (360 °F).

Celsius values in brackets are converted from the sources’ Fahrenheit figures and rounded. When a recipe gives its own temperature, use it: Pastry Arts Magazine notes that caramels and marshmallows can be cooked to different temperatures depending on the texture you want, with lower temperatures giving a softer result.

Why the temperature keeps rising

Water boils at 100 °C (212 °F) at sea level, but a sugar syrup boils hotter. As it boils, water leaves as steam, the syrup that remains holds a higher proportion of sugar, and its temperature rises (Exploratorium). That makes the thermometer a measure of concentration. The Exploratorium gives about 80% sugar at thread stage, 85% at soft ball, 92% at hard ball, 95% at soft crack and 99% at hard crack. By about 160 °C (320 °F) all the water has gone and what is left is liquid sugar, ready to caramelize.

The highest temperature the syrup reaches decides how it behaves when it cools. A syrup taken to soft ball makes soft candies such as fudge and fondant; one taken to hard crack sets hard and brittle, as in lollipops and nut brittle (Exploratorium).

Adjusting for altitude

Water boils at a lower temperature at altitude, so a syrup reaches each stage at a lower temperature too. Colorado State University Extension advises lowering candy temperatures by 2 °F for every 1,000 feet above sea level, which works out at roughly 1 °C for every 300 metres. The Exploratorium’s rule of 1 °F for every 500 feet is the same rate.

The same extension service lists water boiling at 212 °F (100 °C) at sea level, 208 °F (98 °C) at 2,000 feet (610 m), 203 °F (95 °C) at 5,000 feet (1,524 m) and 193 °F (89 °C) at 10,000 feet (3,048 m). New Mexico State University suggests a more exact method: measure the temperature at which water boils in your own kitchen and lower each target by the difference from 212 °F (100 °C).

Adjusted target (°C) = sea-level target − (100 − your boiling point)
Adjusted target (°F) = sea-level target − (212 − your boiling point)

Worked example: water boils at 95 °C (203 °F) in your kitchen, so the adjustment is 100 − 95 = 5 °C (9 °F). A firm-ball target of 118 °C (244 °F) becomes 113 °C (235 °F), and a hard-crack target of 150 °C (302 °F) becomes 145 °C (293 °F).

The cold-water test needs no adjustment, because it judges the syrup by how it sets rather than by temperature (Colorado State University Extension; New Mexico State University).

Check your thermometer in boiling water

A thermometer that reads a few degrees too high or too low can make you stop a syrup at the wrong stage. The USDA Food Safety and Inspection Service describes a boiling-water check:

1. Bring a pot of clean water to the boil. Distilled water gives the truest result.
2. Put the stem of the thermometer at least 5 cm (2 inches) into the boiling water.
3. Wait at least 30 seconds, until the reading settles, without lifting the stem out.
4. At sea level it should read 100 °C (212 °F). If your thermometer has a calibration nut or dial, adjust it as the maker’s instructions describe.

If it cannot be adjusted, note how far it reads high or low and shift your candy temperatures by the same amount (Exploratorium). At altitude this one reading covers both problems at once: it shows where water boils in your kitchen on your thermometer, which is exactly the number the altitude formula above needs (New Mexico State University).

Crystallisation: causes and fixes

As a cooked syrup cools it holds more dissolved sugar than it normally could, which makes it supersaturated and unstable. Stirring, jostling or stray sugar crystals can start crystals forming and turn the candy grainy (Exploratorium; Colorado State University Extension). Fudge and fondant are meant to contain crystals, but caramels, taffy, brittle and lollipops should stay crystal-free (Exploratorium).

Common causes

• Seeding: undissolved sugar, or crystals from the sides of the pan, getting into the syrup while it cooks or cools (Colorado State University Extension).
• Agitation: stirring a plain sugar-and-water syrup once it boils, or moving non-crystalline candy while it cools (King Arthur Baking; Colorado State University Extension).
• Scraping the pan: Colorado State University Extension advises never scraping out the last of the syrup when pouring candies that should stay smooth, such as caramel, taffy and brittle.

Fixes

• Dissolve the sugar completely before the syrup boils, and pour it into the centre of the pan so grains do not stick to the sides (King Arthur Baking; America’s Test Kitchen).
• Wash crystals off the sides with a wet pastry brush, or cover the pan briefly so the steam dissolves them (King Arthur Baking; Colorado State University Extension).
• For a plain sugar-and-water syrup, stop stirring once it boils. Let non-crystalline candy cool undisturbed and pour without scraping the pan (Colorado State University Extension). Dairy caramel mixtures are different: follow the recipe’s stirring instructions to prevent scorching. King Arthur Baking’s Mom’s Caramels, for example, requires constant stirring.
• Add an interfering agent. Glucose or corn syrup gets in the way of sucrose crystals, and some lollipop recipes use as much as 50% corn syrup. An acid such as lemon juice or cream of tartar splits some sucrose into glucose and fructose, and fat such as butter also interferes (Exploratorium).

Keep candy temperatures with your recipes

CookBook saves recipes from websites, social posts, photos and cookbooks and keeps them organised, so your fudge, toffee and Italian meringue recipes sit together. In cooking mode you can change servings and the measurement system. Ingredient amounts scale but cooking times do not, so trust the thermometer and the cold-water test rather than the clock when you make a bigger or smaller batch. See how to add and import recipes.

Sources

King Arthur Baking: Mom’s Caramels

• NIST: Metric kitchen, culinary temperature
• Exploratorium: Sugar stages
• Exploratorium: What is sugar?
• King Arthur Baking: How to make caramel
• Pastry Arts Magazine: The science of sugar
• Colorado State University Extension: Candy making at high elevation
• Colorado State University Extension: High elevation food preparation (2023)
• New Mexico State University: High-altitude cooking (Guide E-215)
• USDA Food Safety and Inspection Service: Food thermometers
• America’s Test Kitchen: Salted caramels