Sugar Boiling the Syrups in the Vacuum Pans

One of the most practical means of measuring this important variable is by the temperature of the boiling syrup at a known absolute pressure or by reference to the temperature of water boiling at the same pressure. The so-called “Boiling Point Elevation” or “BPE” has long been used for this purpose. A considerable amount of care must be exercised in making the temperature measurements if they are to yield an accurate measure of supersaturation because the BPE range of interest covers only a few degrees Centigrade. The normal temperature gradients in vacuum pans make intolerable errors if the syrup temperature is taken even a short distance below the boiling surface. This poses some mechanical problems due to changing pan level but one widely used technique is to take the temperature of vapor leaving the pan as it will be at the surface temperature. More of measurement problems later.