Food Chemistry

20.1 Beer 901

tanks. With a wort extract content of 12%, 4% of
ethanol is produced during fermentation.
The young “green” beer is stored for 1–2 months
in tanks at 0–1◦C for secondary fermentation.
The beer is clarified by settling of the yeast
and separation of protein-polyphenol complexes
(cf. 18.1.2.5.8). The yeast multiplies attaining 4
to 5 times the original quantity and is harvested
after fermentation. It is used several times until
it is no longer biologically pure or it loses
fermenting power.

20.1.5.2 Top Fermentation

Primary fermentation proceeds in fermentation
tanks, but at higher temperatures (18–24◦C) than
bottom fermentation, and requires a total time of
ca. 3 days. The yeast builds a solid cap at the
top of the tank. It is skimmed off into individ-
ual fractions (hops flock, yeast flock, post-flock).
The secondary fermentation is a very slow pro-
cess and may continue in tanks or bottles. Top
fermentation is used mostly in England and Bel-
gium, while in Germany it is used in the pro-
duction of “Kölsch”, “Altbier” and “Weiss” beer,
a light tart ale made from wheat.

20.1.5.3 Continuous Processes,
Rapid Methods

Several continuous processing methods pro-
vide accelerated fermentation. They make use
of thermophilic yeasts, higher fermentation
temperatures and more intensive wort aeration.

20.1.6 Bottling

After ageing, beer is filtered through cotton
filter pads and some silicates, often having been
preclarified through a kieselguhr pad or by
centrifugation. Then, with the aid of a special
cask/keg filling apparatus, it is foamlessly filled
into transportable casks or metal cisterns. In add-
ition to impregnated oakwood casks, specially-
lined iron, aluminum or V 2 A steel containers
are also acceptable. Bottle filling proceeds from

a “bottle tank” in a fully automated process.

Tin-plated or aluminum cans are also used.

Pasteurization gives the beer biological stability

for overseas export. To avoid cloudiness due to

protein precipitation and changes in flavor, the

beer is heated to 60–70◦Cinawaterbathorby

steam. The beer is often pasteurized at 62◦Cfor

20 min. For sterile filling the beer is heated to

70 ◦C for 30 s or is passed through microfilters

(with pore size less than the size of bacteria) and

then poured into sterilized bottles or cans.

Temperature fluctuations during storage and

transport must be avoided if beer quality is to be

preserved.

20.1.7 Composition

20.1.7.1 Ethanol

The ethanol content, which has a very important

influence on the aroma, is 1.0–1.5% by weight for

a low fermented extract-rich beer, 1.5–2.0% for

a weak or thin beer, 3.5–4.5% for a full beer, and

4 .8–5.5% for a strong beer. Higher alcohols, such

as 2-methylbutanol, 3-methylbutanol, methyl-

propanol and 2-phenylethanol, are also present in

very small quantities.

20.1.7.2 Extract

The nonalcoholic constituents of beer vary within

a wide range from 2–3% for plain beers to 8–

10% for strong beers. These constituents are the

beer solids and consist of to 80% carbohydrate,

mostly dextrins. It is possible to calculate the

solids content of the original wort before fermen-

tation from the solids content (E, weight %) and

alcohol content (A, weight %) of the beer prod-

uct. The calculation is based on the fermentation

equation: 2 parts by weight of sugar equal 1 part

by weight of alcohol. Theinitial solids content of

wort, which actually represents a measure of malt

utilization, is designated as “stemwort” (St) and

can be calculated by the formula:

St=

100 (E+ 2 .0665 A)

100 + 1 .0665 A

(20.5)