Food Biochemistry and Food Processing (2 edition)

BLBS102-c33 BLBS102-Simpson March 21, 2012 14:5 Trim: 276mm X 219mm Printer Name: Yet to Come

628 Part 5: Fruits, Vegetables, and Cereals

fermentation needs to be performed. During this fermentation,

major flavor-active compounds are produced (and some of them

are again metabolized) by the yeast cells. The metabolism of

the most important fermentation by-products during main and

secondary fermentation is discussed in detail. The latest trend

in beer fermentation technology is the process intensification

using immobilized cell technology (ICT). This new technology

is explained and some illustrative applications—on small and

large scale—are discussed.

THE BEER BREWING PROCESS

The principal raw materials used to brew beer are water, malted

barley, hops and yeast. The brewing process involves extracting

and breaking down the carbohydrate from the malted barley to

make a sugar solution (called “wort”), which also contains es-

sential nutrients for yeast growth, and using this as a source of

nutrients for “anaerobic” yeast growth. During yeast fermenta-

tion, simple sugars are consumed, releasing heat and producing

ethanol and other flavoring metabolic by-products. The major

biological changes, which occur in the brewing process, are cat-

alyzed by naturally produced enzymes from barley (during malt-

ing) and yeast. The rest of the brewing process largely involves

heat exchange, separation, and clarification, which only pro-

duces minor changes in chemical composition when compared

to the enzyme catalyzed reactions. Barley is able to produce all

the enzymes that are needed to degrade starch,β-glucan, pen-

tosans, lipids, and proteins, which are the major compounds of

interest to the brewer. An overview of the brewing process is

shown in Figure 33.1, where also the input and output flows are

indicated. Table 33.1 gives a more detailed explanation of each

step in the process.

CARBOHYDRATE

METABOLISM—ETHANOL PRODUCTION

Wort Carbohydrates Uptake and Metabolism

Carbohydrates in wort make up 90–92% of wort solids. Wort

from barley malt contains the fermentable sugars sucrose, fruc-

tose, glucose, maltose, and maltotriose together with some

Malt

Wort cooling and

aeration

Primary fermentation

Beer filtration

Maturation and

conditioning

Beer stabilization

Beer packaging

Brewing water

Unmalted cereals

Hops/hopproducts

Syrups

Yeast

Spent grains

Hot trub

Spent hops

Yeast

Cold trub

Yeast

Milling

Mashing

Wort separation

Wort boiling

Wort clarification

Figure 33.1.Schematic overview of the brewing process (input flows are indicated on the left side and output flows on the right side).