Good Malt - Good Beer? How does malt influence beer appearance? Malt is the soul of beer!
Malt contributes two classes of compounds to beer that impart colour: these are polyphenols and melanoidins. In addition, malt contributes an enzyme called polyphenol oxidase which modifies the colour of the polyphenolic material during mashing and run-off. Speciality malts such as chocolate, amber, and Cara pils malts can be used to impart distinctive colours to beer and to provide more control over beer colour.
Haze material contains two major components - protein and polyphenol. Malt and hops are the two sources of polyphenols in beer: proteins are generally contributed by malt. During the beer production process these two groups of components are encouraged to react to produce insoluble complexes. In this way they are gradually eliminated from the process stream.
In most beer styles, malt is the primary source of beer foam proteins and polypeptides. In beer, these materials are cross-linked by hop-derived iso-alpha-acids, which are in turn bound to divalent metal ions, to give a stable three-dimensional structure around bubbles of CO2 gas. The identity of these malt-derived foam proteins has been much debated, especially the point of whether they differ from those involved in haze production. As yet there is no definite agreement. However, the consensus appears to be: (i) Foam proteins have a range of sizes, though protein fractions with molecular masses of 40,000, and 8,000 - 18,000 play an important role; (ii) They are amphipathic: that is, they have both hydrophilic and hydrophobic properties. The hydrophobic properties of the foam proteins are particularly important; (iii) Substituent groups on the foam proteins (eg sugar residues) may be important.
To make up for deficiencies in malt quality, process performance, or trade dispense practices, some breweries use foam stabilizers. The most common of these is propylene glycol alginate (PGA). PGA protects foams against lipid damage. Malt contains a natural foam stabilizer, though its importance in commercial brewing operations has yet to be clarified. Lipid transfer protein (LPT1) can bind lipids, that might otherwise destabilize beer foam.