Sugar Syrup Calculator

What the numbers rest on

The concentration figures are Claassen's empirical boiling-point table for pure sucrose at sea level, as reproduced in Hugot's Handbook of Cane Sugar Engineering: 80 percent at 229 °F, 85 at 235, 90 at 247, 94 at 267. Figoni's teaching table agrees with it to half a degree where they overlap, and supplies the one figure above it, 98 percent at 280 °F. The calculator interpolates between those rows and says so when a reading has gone past them, because above about 99 percent the syrup is no longer boiling and its temperature tracks caramelization rather than concentration.

Elevation is handled by physics, not by the 1 °F per 500 ft rule. Air pressure falls with altitude along the standard-atmosphere curve and water boils where its vapor pressure meets that air pressure; the calculator computes both. The linear rule is right at 1,000 ft and over-corrects by about a degree for every 5,000 ft beyond, which is why the two disagree by a degree at Denver. Weather moves the boiling point by about as much as the last thousand feet, so the better input is the temperature your water actually boils at, measured on the day, which also corrects your thermometer.

A refractometer reads concentration directly and needs no elevation correction, but its Brix scale is calibrated for sucrose alone. A syrup carrying glucose syrup or invert sugar reads as equivalent sucrose, and the true solids differ by an amount that grows as the sucrose fraction falls; the stage is still a fair guide, the percentage is not exact. The same doctoring nudges the thermometer the other way: at the same total solids a doctored syrup boils slightly hotter, so it reads a little less concentrated than the table says.

The physics, the reconciled stage table, and the sources: Sugar Syrup Physics · The confections and the crystalline-versus-glassy divide: Chocolate & Confectionery · Leavening, sugar, and liquid corrections for elevation: Altitude Adjustment