After doing some research on the topic of brewing sugars, I have put together a quick article that sums up all of the things I have learned.  Grains are soaked in approx. 150 degree water to extract these sugars, this is called mashing.   Next the fermentation process uses yeast to convert these sugars in the wort into alcohol and CO2.  The common sugars associated with brewing, there prevalence in wort, and how yeast breaks them down are described below.

Building Blocks

Here are the very basic things to know about the sugars extracted from grains during brewing.

  • Sugar is basically a ringed structure made up of carbon, oxygen, and hydrogen
  • A sugar ring is named by how many carbon atoms are attached to it.
  • Common brewing sugars, such as glucose and fructose are made up of a single hexose (6 carbon atoms, chemical formula C6H12O6)
  • A single hexose is called a monosaccharide.
brewing sugar -- glucose

brewing sugar -- glucose

Common monosaccharides that existing in brewing sugars are glucose, fructose, and galactose.  When two monosaccharides join they form another sugar structure called a disaccharide.  Common disaccharides that exist in brewing sugars are sucrose and maltose.  Sucrose is made up of a glucose molecule and fructose molecule, while maltose is made up of two glucose molecules.  When three monosaccharides join they form another sugar structure called a trisaccharide.  The most common trisaccharide that exists in brewing sugars is maltotriose, which is made up of three glucose molecules.  When monosaccharides join in structures of 4 or more the resulting structures are called dextrin, which is not fermentable by beer yeast.  Pure dextrin is actually added to some beers during the boil to increase body in the final product, our Northern English Brown ale is a good example.

brewing sugar -- glucose + fructose = sucrose

brewing sugar -- glucose + fructose = sucrose

Common Brewing Sugars Breakdown

  • Monosaccharides — glucose, fructose, and galactose
  • Disaccharides —  sucrose and maltose
  • Trisaccharides — maltotriose

Prevalance in Wort

Here are the typical percentages of the 5 common brewing sugars in wort.

  • 45%   Maltose
  • 14%   Maltotriose
  • 8%     Glucose
  • 6%     Sucrose
  • 2%     Fructose
  • 25%   Unfermentable dextrins

As a side note according to sweetness the order follows this – Fructose(sweetest), sucrose, glucose, maltose, maltotriose(least sweet). 


How does beer yeast break down these sugars?

Beer yeast break down brewing sugars by first working on the sucrose structure.  The yeast will break down the sucrose into its glucose and fructose components.  It will then consume the glucose, followed by fructose then maltose and finally maltotriose in that order. 

The yeast usually use two different enzymes to break down the different sugars.  To break down sucrose the yeast use an enzyme called invertase, which breaks them down outside the yeast cell.  To break down maltose and maltotriose the yeast use an enzyme called maltase, which breaks them down inside the yeast cell.  The take away here is that the sugars are broken down into monosaccharides before being completely utilized by the yeast.  The science behind what the yeast is actually doing is a huge topic on its own.

yeast eating sugars in fermentation vessel

yeast eating sugars in fermentation vessel

Hopefully this article was useful in understanding more about some of the basic chemistry in brewing, if you want to know more just comment below.