Sunday, February 17, 2013

Wort Sugars

For yeast to ferment multi-chain sugars it must first be broken down to a single chain by an enzyme. Whether yeast can produce these required enzymes is dependent on its genetics. (1) So if a typical wort split into several different fermentations, and each is inoculated with a different yeast, each one should fall into a bin representing it's enzyme capability.

Chain length(2)
Fermentation order(1)
Wort composition(1)
4 or more
Un fermentable

To find out more precisely the sugar content of the dried malt extract you may be using search for the data sheet provided by the maltster.  For example, one data sheet from Briess shows a similar break down to the one shown in the table above although the fructose seems to be replaced by more glucose.  This indicates that CBW(R) Golden Light DME is composed of 13% Glucose, 48% Maltose, 14% Maltotriose, and 19% Higher Saccharides. (3)

Given this wort compositions I would expect fermenting microorganisms to fall into four categories:

10% attenuation
  • only capable of fermenting simple sugars.
55% attenuation
  • capable of fermenting 2 chain sugars but not 3 chain.  
  • Eg. Wine yeast
75% attenuation
  • capable of fermenting 3 chain and shorter sugars.
  • Eg. Brewing yeast
100% attenuation
  • capable of fermenting all sugars.  
  • Eg. Hyper attenuating bacteria and possibility Brett (Brettanomyces)

Different strains of yeast can be used to ferment a wort in order to determine the sugar content. Dry malt extract was used to create five worts of different gravities.  These were split into a total of 15 cultures and were allowed to ferment to completion with three different yeasts.  The brewers yeast attenuated the wort 62%, while the wine yeast attenuated the wort 40%.  From this it seems that the dry malt extract is 40% one and two chain sugars, 22% three chain sugars, and the remaining 38% is four or larger chain sugars.

the y axis on the left is the apparent attenuation.
the x axis on the bottom is the original gravity of the wort.

There are other factors that effect attenuation.  Most notably is available oxygen.  For more accurate results of this test a stir plate or agitation table will likely produce more consistent results than culture tubes. 

For recipe formulation this fast ferment test can be used to asses brewing ingredients to asses their impact to alcohol and final gravity in both cider and beer making.

Another useful application, and perhaps more interesting, would be to determine sugar composition produced by different mash temperatures.  A sample could be pulled from the mash periodically and then quickly boiled to denature the enzymes.  These samples could then be evaluated with a fermentation test to determine the sugar composition.

For more details on sugar composition through the mash see this post:


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