For the past few months, I've been toying with the idea that some of the tannins within sorghum, is what may be causing the astringent/metallic flavor that many people describe when they come into contact with sorghum-based gluten free beer. 

The loose reasoning behind this is that too much tannin in any product will cause a tart, astringent or metallic flavor.  Not enough tannin in some things, means that the flavor can absent.  Strawberries and cranberries have a tartness to them due to their tannins, they just wouldn't be the same without them.  Black tea also has tannin, which gives it that dry flavor.  Enough tannin in tea makes it taste good, too much tannin, usually from overextracted tea, makes a person's mouth feel dry.

The hardest part though, is that the word tannin encompasses a large range of organic compounds and those compounds are different from item to item. So some items can have the same amount of total tannins (lets say 12 for each) but both can have a completely separate set of 12, and thus the tannin has a different effect. 

Apparently sorghum has about twice as many different phenolic and flavinoid compounds as barley does, and only a few of them overlap.  So the desired experiments would be twofold, to reduce tannin compounds overall, or even to remove one type of tannin, until the desired effect results. 

Now that second option is definately eliminated for me, and I can't even appropriately do the first set of experiments since I don't have any viable setup, including:  Space, constant temperature & environment, which are crucial to having constant elements in an experiment.  I'll still be doing some loose, not so scientific experiments in the meantime.

One set of experiments is to malt my own sorghum. The enzymatic process involved is said to reduce the amount of tannins.  (Note: Link to scientific paper from 1978)
A second set of experients is to first soak the sorghum in an alkaline solution prior to malting, or even using an enzymatic compound to break the sorghum down to fermentable sugars.  (link to 2010 scientific paper studying the effect of alkaline solution & sorghum tannin amounts)
The third set of experiments is to use a fining compound that will react with the tannin to reduce it during the secondary/clearing process of the beer.  Possible fining compounds include gelatin, isinglass, egg whites.

These (and some other) fining compounds react with tannin, which will drop it out of the solution.  If I'm not too careful though, this will also mean that flavor and body will be removed from the beer as well.  In the meantime, I'm using about a gallon's worth of my first 5 gallon beer to test this out on.

My next set of beer, I expect to be testing this as well, and this will be reported on the next post.