Appears in
Oxford Companion to Wine

By Jancis Robinson

Published 2006

  • About

glucose is with fructose one of the two principal sugars of the grape and of sweet wines. Like fructose, it is a six-carbon-atom sugar, or a hexose.

The two major sugars that accumulate in grapes occur in about equal amounts; at the beginning of ripening, glucose exceeds fructose (up to fivefold), but in wines made with overripe grapes there is less glucose than fructose at the end of fermentation. Glucose also serves a very important function as the major sugar used by the vine for forming glycosides (see also flavour compounds). Common table sugar, sucrose, is made up of one molecule of glucose and one of fructose. See fructose for details of the unusual relationship between these sugars and the grape.