Vol. VII · Starches and Sugars Plate 6 of 11sugar syrup, candy, soft ball, hard crack, boiling point, concentration, thermometer, altitudeMT

Sugar Syrup Stages.

A candy thermometer is really a concentration meter: the hotter a boiling syrup, the less water is left in it.

Boil a syrup of sugar and water and, as water steams off, the remaining syrup gets more concentrated — and because dissolved sugar raises the boiling point (III.7), the temperature climbs. So the thermometer tells you how much water is left. Confectioners name the stages by how a drop behaves when cooled in cold water: thread near 110 °C, soft ball about 112–116 °C (fudge, fondant), firm and hard ball (caramels, nougat), soft crack (toffee) and hard crack about 146–154 °C (brittle, lollipops, 拔丝 spun-sugar coatings). Above about 160 °C the sugar itself begins to break down into caramel (VII.8).

The workshop computes the concentration of a boiling syrup from its temperature — Norrish's water-activity equation up to 80 %, the confectioners' table above — and places it on the stages.

Below: the boiling point of a sucrose syrup against its sugar concentration, with the confectioners' stages, at your altitude; and the concentration at the temperature you choose.

What you will learn
Workshop
Boiling point of sucrose syrups at sea level (Norrish water activity to 80 %, McGee's confectionery table above), shifted by the fall in water's boiling point at altitude. Stage ranges are the standard confectionery ones.

A thermometer that reads water

A syrup boiling at 115 °C is about 85% sugar — soft ball, the stage for fudge and fondant; at 150 °C about 99%, hard crack, with only a trace of water left. Between them the syrup goes from soft and pliable when cooled to glassy and brittle, because less water means a stiffer, then glassy, sugar mass. That is the whole logic of candy making: cook to a temperature, and you have cooked to a water content.

Altitude shifts every stage, because the syrup's boiling point falls with water's: at 2 000 m subtract about 6.7 °C from a sea-level recipe's temperatures. Calibrate the thermometer in boiling water first (I.4) and use the difference. And watch the last stages closely: near hard crack the temperature climbs quickly as the last water leaves, and a few degrees more begins caramelisation.

At the stove

Boil 200 g sugar with 80 g water and a thermometer in the pan. At 112, 120, 135 and 150 °C drop a little into a glass of iced water and feel it: a soft ball that flattens, a firmer ball, flexible threads, then brittle glass. Take great care: boiling sugar is far hotter than boiling water and sticks to skin.

拔丝 dishes — 拔丝地瓜, 拔丝苹果 — coat fried pieces in sugar cooked to the hard-crack stage, so that it pulls into glassy threads as the pieces are lifted; dipped in cold water at the table, the coating sets glass-hard.

Terms

Sugar stages
Named consistencies of cooled syrup — thread, soft ball, hard crack — that correspond to temperatures.
Candy thermometer
A thermometer reading up to about 200 °C, for syrups and frying.
Hard crack
About 146–154 °C: syrup cools to brittle glass.
Altitude correction
Lowering a recipe's syrup temperatures by the drop in water's boiling point.
A boiling syrup's temperature measures its water: each stage is a concentration, from soft ball (about 85 % sugar) to hard crack (about 99 %).

Sources

  1. R. S. Norrish, "An equation for the activity coefficients and equilibrium relative humidities of water in confectionery syrups", J. Food Technol. 1, 1966 (K = −6.47 for sucrose).
  2. Sugar syrup stages by temperature at sea level: thread 106–112 °C, soft ball 112–116 °C, firm ball 118–120 °C, hard ball 121–130 °C, soft crack 132–143 °C, hard crack 146–154 °C, caramel from about 160 °C (standard confectionery tables, e.g. the Culinary Institute of America, Baking and Pastry, 3rd ed., 2015).
  3. IAPWS, Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam (IAPWS-IF97), region 4 (saturation).