2009_Book_FoodChemistry

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 individual
fractions (hops flock, yeast flock, post-flock).
The secondary fermentation is a very slow process
and may continue in tanks or bottles. Top
fermentation is used mostly in England and Belgium,
while in Germany it is used in the production
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 provide
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 addition
to impregnated oakwood casks, speciallylined
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, methylpropanol
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 fermentation
from the solids content (E, weight %) and
alcohol content (A, weight %) of the beer product.
The calculation is based on the fermentation
equation: 2 parts by weight of sugar equal 1 part
by weight of alcohol. The initial 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)