Food Biochemistry and Food Processing

29 Biochemistry and Fermentation of Beer 675

BEER FERMENTATION USING
IMMOBILIZED CELL
TECHNOLOGY

The advantages of continuous fermentation—such
as greater efficiency in utilization of carbohydrates
and better use of equipment—led also to the devel-
opment of continuous beer fermentation processes.
Since the beginning of the 20th century, many dif-
ferent systems using suspended yeast cells have
been developed. The excitement over continuous
beer fermentation led—especially during the 1950s
and 1960s—to the development of various interest-
ing systems. These systems can be classified as
(1) stirred versus unstirred tank reactors, (2) single-
vessel systems versus a number of vessels connected
in series, and (3) vessels that allow yeast to overflow
freely with the beer (“open system”) versus vessels
that have abnormally high yeast concentrations
(“closed” or “semiclosed system”) (Hough et al.
1982, Wellhoener 1954, Coutts 1957, Bishop 1970).
However, these continuous beer fermentation pro-
cesses were not commercially successful due to
many practical problems, such as the increased dan-
ger of contamination (not only during fermentation
but also during storage of wort in supplementary
holdings tanks, which are required since the up-
stream and downstream brewing processes are usu-
ally not continuous), changes in beer flavor (Thorne
1968), and a poor understanding of the beer fermen-
tation kinetics under continuous conditions. One of
the well-known exceptions is the successful imple-
mentation of a continuous beer production process
in New Zealand by Morton Coutts (Dominion Brew-
eries) that is still in use today (Hough et al. 1982,
Coutts 1957).
In the 1970s, there was a revival of interest in de-
veloping continuous beer fermentation systems due
to the progress in research on immobilization bio-
processes using living cells. Immobilization allows
fermentation processes with high cell densities, re-
sulting in a drastic increase in fermentation produc-
tivities compared with the traditional time-consuming
batch fermentation processes.
In the last 30 years, immobilized cell technology
(ICT) has been extensively examined, and some
designs have already reached commercial exploita-
tion. Immobilized cell systems are heterogeneous
systems in which considerable mass transfer limita-
tions can occur, resulting in a changed yeast cell

metabolism. Therefore, successful exploitation of

ICT requires a thorough understanding of mass

transfer and of the intrinsic yeast kinetic behavior of

these systems.

CARRIERMATERIALS

Various cell immobilization carrier materials have

been tested and used for beer production/bioflavor-

ing. Selection criteria are summarized in Table 29.5.

Depending on the particular application, reactor

type, and operational conditions, some selection cri-

teria will be more appropriate. Examples of selected

carrier materials for particular applications are tabu-

lated in Table 29.6.

APPLICATIONS OFIMMOBILIZEDCELL

TECHNOLOGY(ICT) IN THEBREWING

INDUSTRY

Flavor Maturation of Green Beer

The objective of flavor maturation is the removal of

diacetyl and 2,3-pentanedione and their precursors,

-acetolactate and -acetohydroxybutyrate, which

are produced during the main fermentation (see

above). The conversion of -acetohydroxy acids to

the vicinal diketones is the rate-limiting step. This

reaction step can be accelerated by heating the

beer—after yeast removal—to 80–90°C during a

couple of minutes. The resulting vicinal diketones

are subsequently reduced by immobilized cells into

their less flavor-active compounds.

The traditional maturation process is character-

ized by a near-zero temperature, low pH, and low

yeast concentration, resulting in a very long matura-

tion period of 3–4 weeks. Using immobilized cell

technology, this long period can be reduced to 2

hours. An ICT maturation process using a packed-

bed bioreactor with diethylaminoethyl (DEAE) cel-

lulose beads has been successfully integrated in

Synebrychoff Brewery (Finland) for the treatment of

1 million hL/year (Pajunen 1995). Alfa Laval and

Schott Engineering developed a maturation system

based on porous glass beads (Dillenhöfer and Rönn

1996). This system has been implemented in several

breweries in Finland (Hyttinen et al. 1995), Bel-

gium, Germany, and elsewhere. The German com-

pany Brau and Brunnen has also shown an interest

in the Alfa Laval maturation technology. In 1996, a