2009_Book_FoodChemistry

20.1 Beer 905
Fig. 20.3. Terminology for the description of odor and taste notes of beer (American Society of Brewing Chemists,
according to Meilgaard, 1982)
Nine of the terms given in Fig. 20.3 describe the
most important odor and taste characteristics of
a good beer (Table 20.8). They are also suitable
for the differentiation of different types of beer
(Table 20.8).
Foaming is an important criterion of the taste of
beer. A distinction is made between foam volume
(produced by the content of carbon dioxide),
foam density, and especially foam stability
(caused by protein degradation products, bitter
hop compounds, and pentosans). Lower fatty
acids that are present in beer bouquet act as defoamers.
Beer defects detract from the odor and taste and
are caused by improper production and storage.
An example of a taste defect is the harsh, hard,
bitter taste produced by the oxidation of polyphenols
and some hop constituents. A flat taste, as
already mentioned, comes from a low content of
carbon dioxide. Diacetyl and ethanal in concentrations
greater than 0.13 mg/l and 25 mg/l respectively,
produce a taste defect. Acceleration
of fermentation caused, e. g., by intensive stirring
of the wort, raises the content of diacetyl
and higher alcohols in the beer and lowers the
content of esters and acids. On the whole, the
aroma is negatively influenced. Higher concentrations
of ethanal can arise, e. g., at higher fermentation
temperatures and higher yeast concentrations.
Beer is very sensitive to light and oxidation. The
“light” taste is due to the formation of 3-methyl-