Impurities in White Sugar

Appears in
On Food and Cooking

By Harold McGee

Published 2004

  • About
It turns out that the tiny fraction of impurities in table sugar can make a noticeable difference in its color and flavor. Make a concentrated syrup from just water and sugar and it will have a yellow, sometimes hazy cast, thanks to large carbohydrate and pigment molecules that either get trapped between sucrose molecules as they crystallize, or remain stuck to the crystal surface. Beet sugar in particular sometimes carries earthy, rancid off-odors. Where sugarcane grows above the ground and is so perishable that it is processed immediately after harvest, the beet grows underground and may be stored for weeks or months between harvest and processing, during which time it can be tainted by soil bacteria and molds that remain on its surface. In addition, beet sugar sometimes carries traces of defensive chemicals called saponins, which resemble soaps. These are known to cause the development of a scum in syrups, and may also be responsible for the poor baking performance sometimes attributed to beet sugar. (This reputation may be an undeserved legacy of the early 20th century, when refining techniques weren’t as effective and the quality of beet sugar often didn’t measure up to that of cane sugar.)