There has been a HBD thread in which I have suggested crushing coarse and concentrating on gelatinisation, others have suggested that, except for the leafy husk, flour is the ideal crush. The argument has been about extract VS undesirable polyphenol extraction and it has puzzled some that crush should influence polyphenol extraction.
I am always puzzled by brewers' tendency to lump all parts of a chemical class together as though they were the same, beers aren't. The logical fallacy of summation and division is best refuted in the advertising expression, "oils ain't oils". (sophistry sometimes contains a kernel of truth)
Phenols ain't phenols and husks ain't husks either.
Beer has a complex mixture of phenolic compounds from about 150 mg/l to 350 mg/l in concentration. About 2/3 are malt derived and 1/3 hop derived. They fall into two broard (some say "vague"!) categories, a)the semi-volatile Monophenols (phenolic acids, alcohols and amines) and Monomeric phenols (flavonoids, anthocyanogens, catechins and flavanols) and b)the non-volatile condensed Dimeric and Polymeric phenols (polymers of the above).
The volatile phenols are aroma active compounds and originate from raw materials, processing and yeast fermentation. e.g. Ferulic acid from barley is reduced by Bavarian wheat yeasts to the prized aromatic Vinyl Phenol, 4-vinylguaiacol. Residual chlorine from municiple water treatment, natural water or brewer's sanitisers can readily combine with simple phenols to produce the medicinal aroma of the Chlorophenols with very low thresholds (<1 microG/litre). Wild yeasts and bacteria will also preduce undesirable phenolic aromas. It is thought that during boiling some Phenolic Acids are decarboxylated to flavour active compounds which are oxidized to the corresponding aldehydes. 4-hydroxycinnamic acid is a suspect here. Phenolic aroma compounds seem to fall into the desirable Floral range, or the undesirable Ethereal (Bandaid-tm) range.
Amomg the larger condensed phenols, it is not only *polyphenols* that are the problem, but *oxidisable polyphenols*. There are not many of these oxidisable phenols in hops. The simpler phenolic molecules are more polar, i.e. their relatively simple structure has more pronounced spots of unbalanced charges, they are electrically dipolar. Without going into detail, polar molecules are very soluble and in fact, the vast majority of all phenolic compounds are extracted with the first runnings!
Eventually all simple phenols will complex into polyphenols under acid conditions and oxidise and complex with protein into haze. However good beer doesn't last long enough for this to happen significantly, it gets harvested.
The real problem of haze and astringency is the existing small fraction of less polar, i.e. more complex and large, polyphenols. Many fingers have been pointed at Catechines (flavan-3-ols) and Anthocyanogens (flavan-3,4 diols), and especially their polymers, in the formation of haze. However some well known brewing lawyers claim that, while not exactly innocent, they are no more guilty than the rest of the population. (a new legal defence?)
As you would have guessed by now, the polyphenols are not so soluble and if dissolved by higher pH water (>5.5), are repulsed by the polar medium they are in. They thus tend to floc together like friends in a hostile crowd (hydrophobic force) and, with catalysts like metal ions and oxygen, complex with other large (and less soluble) molecules fairly quickly. This is the unsightly but essentially tasteless so-called "tannin-protein haze". (it actually contains many other components of the wort). The protein neutralizes the tanning power of tannoids by forming essentially "tanned" bonds. Tannoids, on their own, have a definite dry astringent taste!
The oxidized polyphenols with tanning power (MWt 700-1000) are called "tannoids" (or tannigens) and they try to turn your taste buds into leather. They do this by covalently crosslinking proteins in your taste buds just as they do in tanning leather and forming haze. They were not intended to do this, they actually seem to be in the *"husk fraction"* (my emphasis) as an astringent inhibitor of fungal and bacterial attack on the barley corn and perhaps a growth inhibitor.
The oxidized polyphenols in sweet wort will *readily complex out* as hot break. Despite their size, they are a *first and middle runnings* extraction problem. These are best controlled by recycling wort through the hot break in the grain bed, or vigorous boiling to form hot break during the boil phase.
The unoxidized, *oxidizable* polyphenols are less soluble and a *late runnings problem* and a large portion can survive (uncomplexed & unprecipitated) into the hopped wort, waiting for oxygen so as to cause haze and astringency problems by becoming Tannoids. These are best controlled by terminating the sparge early at SG 1.015, keeping sparge water pH<5.5,(see Ken Schwartz's new Brewater software with acid additions), keeping sparge temperature below 75C, and crushing your malt coarse.
Polyclar (tm), the "plastic protein" used as a polyphenol fining, removes some of these more active oxidisable and oxidised polyphenols to buy some time for the brewer. The less polymerised phenols will eventually polymerise to replace those removed, beer remains an unstable product.
The sparge process removes extract from *between* and from *within* the kibble of the grain bed. The osmotic leaching process of removing extract (of anything soluble) from *within* bits is slowed down if the bits are big. The solvent (water) simply has further to penetrate.
If the big bits are the "husk fraction",i.e. low in fermentable extract, high in oxidizable polyphenols, then this crush is benficial for reduced polyphenol extraction.
If the big bits happen to be starchy Endosperm bits, then advanced gelatinization of starch is beneficial for better extract of sugar.
Crush coarse, gelatinise well! (See Gelatinisation 101)
Charlie (Brisbane, Australia)