Beer : Health and Nutrition

The Basics of Malting and Brewing 81
always survives into malt (Bamforth & Barclay 1993). Unless it is properly degraded it
renders the wort extremely viscous, with attendant problems in the operations of separating
the wort from the spent grains and with downstream beer ltration (Bamforth 1994).
Thus some brewers mash-in at low temperatures (say 50°C) to allow the β-glucanase
(which is sensitive to heat) to act. Additionally a heat-stable glucanase from bacteria
(such as Bacillus subtilis) or fungi (such as Trichoderma reesei or Penicillium funiculosum)
may be employed (Bamforth 1985a). Barley has been transformed to express a
heat-resistant β-glucanase, but it is not yet cleared for commercial use (Mannonen et al.
1993). All of these efforts to eliminate β-glucan are important if production problems
are to be avoided, as well as quality problems, for the glucan can cause hazes and precipitates
in beer. The beers that will contain the most residual glucan are those that are
produced with a high charge of barley adjunct, for instance some well-known stouts.
The products of β-glucan breakdown in malting and mashing are not fermentable by
yeast, so they survive into beer. Even those beers in which most of the glucan has been
converted to low molecular-weight oligosaccharides may be of some value as sources of
bre, as it is now understood that any β-linked sugar, no matter how small, may retain
some bene cial properties when they reach the lower gut (Schneeman 1999).
β-Glucan is not the only polysaccharide found in the cell walls of barley, the other
being arabinoxylan. For reasons that are not entirely understood, this seems to survive
malting and brewing more readily than does β-glucan, such that beers tend to contain
more arabinoxylan than glucan (Schwarz & Han 1995). It also ranks as soluble bre. In
the cell wall the arabinoxylan is covalently linked to ferulic acid (Ahluwalia & Fry 1986).
This phenolic acid is released during mashing (McMurrough et al. 1996) and survives
into beer (unless the beer is made with yeasts, such as those used in the fermentation of
wheat-based beers, which contain an enzyme that can decarboxylate the ferulic acid to
4-vinylguiacol, a substance that gives the classic clove-like character to such products).
There is huge interest in ferulic acid as an antioxidant (Kroon & Williamson 1999).
Proteins, polypeptides and amino acids
The presence of polypeptide material in beer is important for the contribution it makes
to foam (Bamforth 1985b). In the processes of malting and brewing, the native proteins
of barley undergo considerable degradation and denaturation, such that those present
in the nished beer bear little resemblance to those found in the barley kernel. While
polypeptides can be bene cial for foaming, they are detrimental in another respect: they
can crosslink with polyphenols to form hazes (McMurrough & Delcour 1994).
The amino acids in beer provide no real bene t to the beer. If present in excess, they
potentiate infection of a product by acting as nitrogen sources for spoilage microorganisms.
This is why brewers seek to optimise the level of amino acids in wort, so that the
yeast uses up all that is readily assimilable.