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

644 Part 5: Fruits, Vegetables, and Cereals

Two 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 The heat treatment has been replaced by an ̈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 Beer

The 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 Bacteria

The 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 Fermentation

During 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.