Beer : Health and Nutrition

80 Chapter Three
Carbohydrates
While most of the sugar found in wort is fermented to ethanol by yeast, some carbohydrates
remain in the beer. Furthermore, extra sugars (‘primings’) may be added to
sweeten the nal product.
The carbohydrates surviving into beer from wort are the non-fermentable dextrins
and some polysaccharide material. The dextrins are remnants of starch degradation,
whereas the polysaccharides derive from cell walls in barley.
Most of the starch in the endosperm of barley survives malting, because it is relatively
resistant to enzymatic hydrolysis over anything other than prolonged contact
times. However, if starch is gelatinised (which can be likened to melting) by heat treatment,
then its constituent molecules, amylose and amylopectin, become much more
accessible to enzymes. Thus the start of brewing involves gelatinisation, typically at
65°C, a stage known as ‘conversion’. Other cereals, which may be used as adjuncts,
have starches that need higher gelatinisation temperatures, e.g. rice and corn, in which
starch gelatinises over the range 70–80°C. As stated above, amylase enzymes in the
malt degrade the gelatinised starch to fermentable sugars; however, a proportion (usually
around 20–25%) remains in the form of unfermentable dextrins. A range of beers
is available, which are termed ‘super-attenuated’ but generally marketed as ‘light’, in
which all of the available starch is converted into ethanol. To effect this, an exogenous
heat-stable glucoamylase or pullulanase of microbial origin is often added to the mash
or to the fermenter (Bamforth 1985a). It is not obligatory to approach the problem in
this way. By judicious use of the mashing regime, and also perhaps the addition of an
extract of lightly kilned or unkilned malt to the fermenter, the enzymes native to malt
are suf cient to deal with all the dextrins.
The world’s rst approved, genetically modi ed (GM) brewing yeast was transformed
to express a glucoamylase; however, as yet this strain has not been used in any commercial
operation (Hammond & Bamforth 1994). Indeed, no GM material is knowingly
or deliberately introduced into beer by any brewer. The only commodities that are based
overtly on products of gene technology are some of the commercial enzymes. However,
most brewers do not use these and, where they are used, they are added to the mash,
and are denatured and precipitated in the kettle boil. Even so, it needs to be stressed
that GM commercial enzymes are themselves rigorously screened before approval for
commercial use.
Another major carbohydrate component in brewing systems is in the cell walls of
barley, a β-glucan comprising β 1–4 links (as in cellulose) but disrupted by occasional
β 1–3 links. This molecule is very similar to the β-glucan that is found in oats and which
is well known as the ‘soluble bre’ championed as part of oat-based breakfast cereals
(Lasztity 1998). While one of the main purposes of malting is to degrade the cell walls
through the action of β-glucanase enzymes during germination, in practice some glucan