Thoughts on Mash Temperature, Limit Dextrins, and the Effects on Beer

I have been perplexed the past few days trying to reconcile brewing conventional wisdom with comments from Dr. Charlie Bamforth on a recent podcast.  In the podcast, Bamforth gives an excellent review of the enzymes present in the mash and the effects of mash temperature.  At higher mash temperatures, beta-amylase (the enzyme responsible for producing maltose from longer amylose and amylopectin derived oligosaccharide chains) becomes inactivated while alpha-amylase (the enzyme responsible for breaking long amylose and amylopectin chains into shorter oligosaccharides) remains active at quite high temperatures.  The end result is that at higher mash temps, a wort with a greater concentration of unfermentable oligosaccharides (dextrins) would be produced.  All of this we know, right?  Here’s the kicker: Bamforth suggests that these dextrins have no noticeable effect on beer body or mouthfeel … that the only real consequence of a high mash temp is a lower amount of fermentable sugar that would lead to a lower alcohol level in the beer.

As support, Bamforth sites the work of another highly respected researcher also from UC Davis:  Emeritus Professor Michael Lewis (J. Inst. Brew., January-February, 1993, Vol. 99, pp. 31-37).  This is a great article that deals with much more than just dextrins, but the section on dextrins (pp. 34-35) summarizes research findings regarding sensory perception of these compounds in beer.  I highly recommend reading the article (or at least the dextrin section) yourself and drawing your own conclusions, but what I took from it was this:

1. There doesn’t seem to be much scientific support for the commonly accepted notion that dextrins contribute to mouthfeel or ‘fullness’ (body?) of beer.
2. These dextrins are rather tasteless.  So ‘sweetness’ doesn’t seem to be derived from these compounds either.

What are we as homebrewers to make of this?  Does mash temperature do nothing to affect the character of the beer (other than the final ethanol level)?  I find this difficult to accept.  While I realize the sensory evaluation of beer is highly subjective, I just can’t believe that homebrewers and beer judges have been bamboozled into seeing something that’s not really there.  I think there is a definite effect of mash temperature on beer mouthfeel and body but perhaps we are wrong in assigning this effect to the dextrins that are present as a result of the mash conditions.  While there certainly should be more of these dextrins in a higher temperature mash, the research seems to indicate that this alone does not cause the increased body and mouthfeel in the resulting beer.


So what is it then?  Here’s a theory … Maybe it is not the dextrins themselves that produce body and mouthfeel characteristics but rather glycopeptides formed by Maillard type reactions between these dextrins and peptides in the boil.  This could produce molecules with unique properties.  Also, we (as brewers) tend to associate a high mash temperature with a ‘maltier’ beer.  The malty flavors (in malt) are derived from Maillard reactions that occur during kilning.  Perhaps dextrin/peptide Maillard reactions in the boil could give rise to malty flavors as well.  I haven’t yet come up with a scientific way to evaluate this theory … but I’m working on it.