Thursday, 21 January 2016

Hydrolysis gain

Hydrolysis gain was a tax dodge used back in the days when beer was taxed on its original gravity. As beer is now taxed on its alcohol content it is completely obsolete, but I'm not going to let that stop me. Oh no. 

My researches on brewing sugars, of which they'll be more to come if I get round to it, renewed my interest in the process as I'd never really got my head round it. 

It works like this:

Disaccharide plus water        Two monosaccharides
C12H22O11 + H2O 2C6H12O6

This will happen during fermentation as fermenatable disaccharides will be broken down into two monosaccharides e.g. sucrose → glucose + fructose

I couldn't see what the gain was though, as you won't have made any more fermentable material.

 It took a fair bit of rumaging to find the answer but in an old copy of the Brewers Guardian (Oct 2009) I found an article by Charlie Bamforth where he explains:

"The specific gravity of wort of wort will basically depend on how many sugar molecules are present by unit volume"

As original gravity is a measure of density, not fermentable material, lower gravities, and therefore tax bills, could be obtained by having the fermentables in a small number of large molecules rather than a large number of small molecules.

At Bass brewery they took it rather further than using sucrose instead of invert sugar:

"In most standard worts, of course, most of the sugars comprise maltose, However if you mash at a slightly elevated temperature the predominant component will be dextrins ... Consider a molecule of maltose: molecular weight (mw) 342 because it comprises two glucose units (each mw 180) less the molecule of H2O (mw 18) that is lost when they join together. Now take a molecule of dextrin with perhaps 6 glucose units. Its mw is 990 (6 glucoses at 180 each less the five molecules of water lost when they join together). So for every three maltoses (total molecular weight 1,026) we can have one dextrin (mw 990). Specific gravity being weight per unit volume, assuming a similar volume for both a wort that is primarily maltose and another that is primarily dextrin, then the weight of 1 ml of the latter will be less. In other words, in the old days one would have less duty to declare. The trick then was to add an enzyme to the fermenter that would convert the dextrins into fermentable sugars."

So that was how it was done, and one of the reasons why sucrose became more widely used than invert sugars.


  1. Replies
    1. Cheers Jon, glad to see it's not only me that finds it interesting.