The impact of process parameters on flavour profile of alcohol-free beer from a single-stage continuous gas-lift reactor with immobilized yeast

In order to study the formation and conversion of the most important flavour compounds, the real wort used in alcohol-free beer fermentation was mimicked by a complex model medium containing glucose, yeast extract and aldehydes (hexanal, 2-methyl propanal, 3-methyl butanal, furfural). Fermentation experiments were carried out in a continuously operating gaslift reactor with brewing yeast immobilized on spent grains. During continuous experiment, parameters such as oxygen supply, residence time (Rt) and temperature (T) were changed to find the optimal conditions for alcohol-free beer production. The formation of ethanol, higher alcohols (HA), esters (ES), reduction of aldehydes, and consumption of glucose were observed. The results suggest that the process parameters, particularly the oxygen supply, represent a powerful tool in controlling the degree of fermentation and flavour formation carried out by immobilized biocatalyst. Under optimal conditions in the continuous immobilized cell reactor it was possible obtain a fermented model medium with a composition approaching commercial alcohol-free beers.Grant Agency of the Czech Republic - Project 104/06/1418

Fermentação primária da cerveja em contínuo : cinética de imobilização da levedura e qualidade do produto

A one stage continuous primary beer fermentation consisting of brewing yeast immobilized on spent grain particles in a gas lift reactor was studied. The goal of this work was to adjust the flavor of the continuously produced green beer to the desired character by sparging an adequate amount of air and by controlling the fermentation temperature in the immobilized yeast reactor as well as to predict the rate of the brewing yeast immobilization using a kinetic model adapted to the conditions of beer fermentation. The volumetric productivity of the continuous system was approximately 5 times higher than of the batch fermentation. The aroma profile of green beer from the continuous immobilized fermentation, run at zero air flow and temperatures 13 16°C, was fully comparable to that produced by industrial batch technology. Generally, the diacetyl concentration in green beer from the continuous fermentation was higher than in batch process, however, its re-assimilation was enhanced by high total biomass concentration in the system.Foi estudada a fermentação primária em contínuo da cerveja num reactor “gas-lift” com a levedura imobilizada em “drêches”. O objectivo do trabalho foi optimizar as características organolépticas da cerveja verde produzida em contínuo através do controle do caudal e composição do ar e da temperatura. Pretendeu-se também prever a velocidade de imobilização de levedura cervejeira sendo, para tal, desenvolvido um modelo adaptado às condições de fermentação. A produtividade volumétrica do sistema contínuo foi cerca de 5 vezes superior à obtida em descontínuo. O perfil aromático da cerveja verde produzida em contínuo, utilizando um caudal nulo de ar e temperaturas entre os 13 e os 16º C, foi comparável ao perfil aromático da cerveja produzida em descontínuo, numa unidade industrial. Na generalidade das situações testadas, a concentração de diacetilo na cerveja verde obtida em contínuo foi maior que no processo descontínuo sendo a sua reassimilação aumentada pela maior concentração de biomassa no sistema contínuo.Fundação para a Ciência e a Tecnologia (FCT)

Aging of immobilized brewing yeast in a continuous bubble-column reactor

The aim of this work was to study the physiological changes of immobilized brewing yeast Saccharomyces cerevisiae in a continuous reactor. Continuous cultivation was carried out at three different temperatures (15, 20 and 25°C) with an industrial brewing yeast strain (UNICER, Bebidas de Portugal, S.A.). During the continuous experiment the viability of free and immobilized cells was followed using vital staining and flow cytometry. The results of viability determination were used to calculate the specific death rate of the immobilized cells (Kd). Further, the flow cytometry was used to follow the glycogen content of cells and the number of budding cells. The experiments showed that the viability of free cells stayed constant in the course of the whole experiment. Conversely, the viability of immobilized cells decreased during the whole time of the cultivation as well as the viability decreased in the direction from the surface to the depth of the biofilm. The study of the immobilized biomass showed that specific immobilized cell death rate (Kd) was a function of cultivation temperature and that the values of Kd increased with temperature. Higher content of glycogen and a lower count of budding cells was found in immobilized cell fraction.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BPD/3541/2000.MŠMT - MSM 6046137305.UNICER S.A

Flavour formation in continuous fermentations

Fundação para a Ciência e a Tecnologia (FCT

Continuous production of pectinase by immobilized yeast cells on spent grains

A yeast strain secreting endopolygalacturonase was used in this work to study the possibility of continuous production of this enzyme. It is a feasible and interesting alternative to fungal batch production essentially due to the specificity of the type of pectinase excreted by Kluyveromyces marxianus CCT 3172, to the lower broth viscosity and to the easier downstream operations. In order to increase the reactors’ productivity, a cellulosic carrier obtained from barley spent grains was tested as an immobilization support. Two types of reactors were studied for pectinase production using glucose as a carbon and energy source - a continuous stirred tank reactor (CSTR) and a packed bed reactor (PBR) with recycled flow. The highest value for pectinase volumetric productivity (Pv=0.98 U mlˉ¹ hˉ¹) was achieved in the PBR for D=0.40 hˉ¹, a glucose concentration on the inlet of Sin =20 g lˉ¹, and a biomass load in the support of Xi=0.225 g gˉ¹. The results demonstrate the attractiveness of the packed bed system for pectinase production.Fundação para a Ciência e a Tecnologia (FCT) - BD/18203/98, SFRH/BPD/3541/2000

Continuous beer fermentation using immobilized yeast cell bioreactor systems

Traditional beer fermentation and maturation processes use open fermentation and lager tanks. Although these vessels had previously been considered indispensable, during the past decades they were in many breweries replaced by large production units (cylindroconical tanks). These have proved to be successful, both providing operating advantages and ensuring the quality of the final beer. Another promising contemporary technology, namely, continuous beer fermentation using immobilized brewing yeast, by contrast, has found only a limited number of industrial applications. Continuous fermentation systems based on immobilized cell technology, albeit initially successful, were condemned to failure for several reasons. These include engineering problems (excess biomass and problems with CO2 removal, optimization of operating conditions, clogging and channeling of the reactor), unbalanced beer flavor (altered cell physiology, cell aging), and unrealized cost advantages (carrier price, complex and unstable operation). However, recent development in reactor design and understanding of immobilized cell physiology, together with application of novel carrier materials, could provide a new stimulus to both research and application of this promising technology.Fundação para a Ciência e a Tecnologia (FCT

Use of two different carriers in a packed bed reactor for endopolygalacturonase production by a yeast strain

A packed bed reactor (PBR) design was tested for the purpose of continuous pectinase production with yeasts, as a possible alternative to the traditional batch process using fungal cultures. Two different carriers - a porous glass (Siran) and a cellulosic carrier obtained from spent grains (barley) - were used to immobilize Kluyveromyces marxianus CCT 3172, a yeast strain secreting endopolygalacturonase. To improve cell distribution throughout the column, part of the outflow was recycled. Cell loads of 0.204 and 0.247 g(biomass)/g(carrier) were obtained at the top and bottom of the PBR with spent grains, respectively. Using the PBR with Siran as the immobilization support, 0.071 g(biomass)/g(carrier) was the biomass load at the top of the column while at the bottom a value of 0.147 g(biomass)/g(carrier) was found. The highest value for pectinase volumetric productivity (Pv = 1.68 U/ml h) was achieved in the PBR with Siran for a D = 0.260 h(-1) and a glucose concentration on the inlet of S-in = 40 g/l. Both carriers were suitable for pectinase production. The best results were obtained with a high and uniform biomass concentration in the column, together with high dilution rates and total glucose consumption.Fundação para a Ciência e a Tecnologia (FCT) - BD/18203/98 , SFRH/BPD/3541/2000

Continuous beer fermentation with yeast immobilized on spent grains : the effect of operational conditions

Fundação para a Ciência e a Tecnologia (FCT) - SFRH / BPD / 3541 / 2000