BLBS102-c33 BLBS102-Simpson March 21, 2012 14:5 Trim: 276mm X 219mm Printer Name: Yet to Come
644 Part 5: Fruits, Vegetables, and CerealsTwo continuous maturation systems have been implemented
industrially so far: one at Sinebrychoff Brewery (Finland, capac-
ity: 1 million hL per year) (Pajunen 1995) and another system,
developed by Alfa Laval and Schott Engineering (Mensour et al.
1997). They are both composed of a separator (to prevent grow-
ing yeast cells in the next stages), an anaerobic heat treatment
unit (to accelerate the chemical conversion ofα-acetolactate
to diacetyl, but also the partial directly conversion to acetoin),
and a packed bed reactor with yeast immobilized on DEAE-
cellulose granules or porous glass beads (to reduce the remain-
ing diacetyl), respectively (Yamauchi et al. 1994). Later on, the
DEAE-cellulose carriers were replaced by cheaper wood chips
(Virkajarvi 2002). The heat treatment has been replaced by an ̈
enzymatic transformation in a fixed bed reactor in which theα-
acetolactate decarboxylase is immobilized in special multilayer
capsules, followed by the reduction of diacetyl by yeast in a
second packed bed reactor (Nitzsche et al. 2001).Production of Alcohol-Free or Low-Alcohol BeerThe classical technology to produce alcohol-free or low-alcohol
beer is based on the suppression of alcohol formation by ar-
rested batch fermentation (Narziss et al. 1992). However, the
resulting beers are characterized by an undesirable wort aroma,
since the wort aldehydes have only been reduced to a limited
degree (Collin et al. 1991, Debourg et al. 1994, van Iersel et al.
1998). The reduction of these wort aldehydes can be quickly
achieved by a short contact time with immobilized yeast cells at
a low temperature without undesirable cell growth and ethanol
production. A disadvantage of this short contact process is the
production of only a small amount of desirable esters.
Controlled ethanol production for low-alcohol and alcohol-
free beers have been successfully achieved by partial fermen-
tation using DEAE-cellulose as carrier material, which was
packed in a column reactor (Collin et al. 1991, Van Dieren
1995). This technology has been successfully implemented by
Bavaria Brewery (The Netherlands) to produce malt beer on an
industrial scale (150,000 hL/year) (Pittner et al. 1993). Several
other companies—that is, Faxe (Denmark), Ottakringer (Aus-
tria), and a Spanish brewery—have also implemented this tech-
nology (Mensour et al. 1997). In Brewery Beck (Germany), a
fluidized-bed pilot scale reactor (8 hL/day) filled with porous
glass beads was used for the continuous production of nonal-
coholic beer (Aivasidis et al. 1991, Breitenbucher and Mistler ̈
1995, Aivasidis 1996). Yeast cells immobilized in silicon carbide
rods and arranged in a multichannel loop reactor (Meura, Bel-
gium) have been used to produce alcohol-free beer at pilot scale
by Grolsch Brewery (The Netherlands) and Guinness Brewery
(Ireland) (Van De Winkel 1995).
Nuclear mutants ofS. cerevisiaethat are defective in the
synthesis of tricarboxylic acid cycle enzymes; that is, fu-
marase (Kacl ́ıkov ́a et al. 1992) or 2-oxoglutarate dehydrogenase
(Mockovciakova et al. 1993) have been immobilized in calcium ́
pectate gel beads and used in a continuous process for the pro-
duction of nonalcoholic beer (Navratil et al. 2000). These strains ́
produced minimal amounts of ethanol and they were also able
to produce much lactic acid (up to 0.64 g/dm^3 ).Production of Acidified Wort Using Immobilized Lactic
Acid BacteriaThe objective of this technology is the acidification of the wort
according to the “Reinheidsgebot”, before the start of the boil-
ing process in the brewhouse. An increased productivity of
acidified wort has been obtained using immobilizedLactobacil-
lus amylovoruson DEAE-cellulose beads (Pittner et al. 1993,
Meersman 1994). The pH of wort was reduced below a value
of 4.0 after contact times of 7–12 minutes using a packed-bed
reactor in downflow mode. The produced acidified wort was
stored in a holding tank and used during wort production to
adjust the pH.Continuous Main FermentationDuring the main fermentation of beer, not only ethanol is being
produced but also a complex mixture of flavor-active secondary
metabolites, of which the higher (or fusel) alcohols and esters
are the most important (Verbelen et al. 2010). In addition, di-
acetyl and some sulfury compounds can cause off-flavors. Since
this complex flavor profile is closely related to the amino acid
metabolism and consequently to the growth of the yeast cells,
differences in the growth metabolic state between freely sus-
pended and immobilized yeast cell systems are most probably
responsible for the majority of alterations in the beer flavor. For
that reason, it is important that the physiological and metabolic
state of the yeast in conventional batch systems is mimicked as
much as possible during the continuous fermentation with im-
mobilized yeast. In the continuous mode of operation, cells are
not exposed to significant alterations of the environment, influ-
encing the metabolism of the cells and consequently the flavor.
Hence, the microbial population of continuous systems lacks the
different growth phases of a batch culture. To imitate the batch
process as much as possible, plug-flow reactors or a series of
reactors can be used. As can be assumed, both the continuous
mode of operation and the immobilization of yeast cells can
influence the beer flavor.
The Japanese brewery Kirin developed a multistage contin-
uous fermentation process (Inoue 1995, Yamauchi et al. 1994,
Yamauchi and Kasahira 1995). The first stage is a stirred tank
reactor for yeast growth, followed by packed-bed fermenters,
and the final step is a packed-bed maturation column. The first
stage ensures adequate yeast cell growth with the desirable FAN
consumption. Ca-alginate was initially selected as carrier ma-
terial to immobilize the yeast cells. These alginate beads were
later replaced by ceramic beads (“Bioceramic©R”). This system
allowed to produce beer within 3–5 days.
The engineering company Meura (Belgium) developed a reac-
tor configuration with a first stage with immobilized yeast cells
where partially attenuation and yeast growth occurs, followed
by a stirred tank reactor (with free yeast cells) for complete at-
tenuation, ester formation, and flavor maturation (Andries et al.
1996, Masschelein and Andries 1995). Silicon carbide rods are
used in the first reactor as immobilization carrier material. The
stirred tank (second reactor) is continuously inoculated by free
cells that escape from the first immobilized yeast cell reactor.