Applications of natural ingredients in alcoholic drinks - Natural Food Additives, Ingredients and Flavourings - page 363

deep freeze, refrigerator or cold room (Bruning 2009). Unfortunately the
compression packing techniques rupture many of the lupulin glands in the hop
cones, and oxidative degradations and other transformations occur during extended
storage periods. Loss of α -acids, in particular, can be extensive (∼50%) after 12
months storage, even at low temperatures. In extreme cases, the carbonyl side
chains of α -acids (Fig. 16.1) are oxidised to short chain carboxylic acids, which
have distinctive cheesy notes. Because of this, some breweries use hop powders,
pellets or extracts to supplement, or to replace entirely, hop cones in the kettle as
pellets do not deteriorate as rapidly as cones (especially if stored at 0-5°C) and
offer a higher degree of α -acid extraction/isomerisation. Table 16.2 lists the main
hop products and their point of use available to the commercial brewer.
Certain hop pellets are made from mechanically enriched powder and are
especially useful for the dry hopping of cask-conditioned ales. Stabilised hop
pellets are prepared by mixing 1-2% (w:w) of magnesium or calcium oxide with
hop powder to convert the α -acids into more stable salts (Briggs et al. 2004;
McKay et al. 2011a).
A majority of modern hop extracts are produced using liquid and supercritical
carbon dioxide (CO 2 ) (at ca. 10°C and 50 atm. pressure) since this allows
collection of multiple hop fractions (aroma compounds (essential oil), β -acids,
α -acids). Hop oil, produced by the low pressure (∼0.02 mm Hg) steam distillation
of hop powder at 25°C can be added either to bright beer during conditioning or
used for the dry hopping of cask-conditioned beers.
During the boiling process of beer production, many of the aroma (essential
oil) and resinous components are either lost to the atmosphere, decompose or
rearrange (as with the acid-catalysed reactions of citrus oil components, terpenoids
of hop are particularly prone to rearrangement when heated under mild acidic
conditions (Clark and Chamblee 1992)).
The conversion of α -acids to the vastly more hydrophilic iso - α -acids (by a ring
contracting rearrangement) is the principle isomerisation (see Fig. 16.3 for the
example of humulone to isohumulone) alongside, for example, various hydrolysis
and oxidation reactions (McKay et al. 2011a). Many of these conversions are
incomplete after traditional brewery boiling times (60-120 minutes), particularly
with regard to iso- α -acid formation, and hence isomerised hop extracts are
often added to post fermented beer (see Table 16.2). This allows the control of
consistent bitterness (expressed as international bittering units (IBU)), which is
commercially important for larger breweries with multiple production sites and
global markets.
Some beers are fl avoured at breweries with ingredients other than or as well as
hops. This fl avouring addition occasionally takes place at the boiling stage, but is
usually carried out during the fermentation or conditioning/maturation stages.
Some examples of naturally fl avoured beers using ingredients including whole
fruits (or concentrates), beans and pods, spices, leaves, needles and oak are shown
in Table 16.3 .
Adjuncts are used in brewing beer to supplement the main ingredients in the
mash (malted barley). The intention of adjunct addition can be to lower the overall

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