53 research outputs found
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
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
Assessment of brewing yeast age based on selective bud scar staining and subsequent fluorescence measurement by flow cytometry
To study the yeast cell aging in continuous beer fermentation processes has a considerable
practical significance. Hence, an expeditious method of yeast age estimation was developed
based on selective bud scar staining and subsequent fluorescence intensity measurement by
flow cytometry. The calibration curve resulting from cytometric determination of average bud
scar fluorescence intensities of cell populations with different average bud scar numbers
showed a good correlation. The combination of flow cytometry with bud scar staining
resulted in a method of rapid cell age estimation particularly suitable for continuous main
fermentation systems with elevated risk of immobilized cell aging.Grant Agency of the Czech Republic - Project 104/06/1418
Preliminary optimization study of alcohol-free beer production in a continuous immobilized cell reactor system
Grant Agency of the Czech Republi
Optimisation of lab-scale continuous alcohol-free beer production
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 selected aldehydes. The fermentation experiments were carried out in a continuously operating gas-lift reactor with brewing yeast immobilised on spent grains (brewing by-product). During the continuous experiment, parameters such as oxygen supply, residence time (Rt), and temperature (T) were varied to find the optimal conditions for the alcohol-free beer production. The formation of ethanol, higher alcohols (HA), esters (ES), as well as the reduction of aldehydes and consumption of glucose were observed. The results suggest that the process parameters represent a powerful tool in controlling the degree of fermentation and flavour formation brought about by immobilised biocatalyst. Subsequently, the optimised process parameters were used to produce real alcohol-free beer during continuous fermentation. The final product was compared with batch fermented alcohol-free beers using the methods of instrumental and sensorial analysis.Ministry of Education, Youth and Sports of the Czech Republi
Flow cytometry for age assessment of a yeast population and its application in beer fermentations
An expeditious method of yeast age estimation was developed
based on selective bud scar staining (Alexa Fluor 488-labelled
wheat-germ agglutinin) and subsequent fluorescence intensity
measurement by flow cytometry. The calibration curve resulting
from the cytometric determination of average bud scar fluorescence
intensities vs. microscopically counted average bud scar
numbers of the same cell populations showed a good correlation
and allowed routine cell age estimation by flow cytometry. The
developed method was applied for yeast age control in traditional
batch and continuous beer fermentations. At the pitching
rates used in industrial beer fermentations, our results support
former findings by locating a gradient of increasing yeast age
from the top to the bottom zone of the fermenter cone. The results
also indicate that in continuous beer fermentation, the increasing
bud scar fluorescence of immobilized cells could help
to schedule the replacement of aged biomass, prior to loss of
viability or deterioration of process performance and product
quality.Grant Agency of the Czech Republic (GAČR 104/06/1418) and MŠMT (MSM
6046137305, Czech Republic)
Continuous immobilized yeast reactor system for complete beer fermentation using spent grains and corncobs as carrier materials
Despite extensive research carried out in
the last few decades, continuous beer fermentation has not yet managed to outperform the traditional batch technology. An industrial breakthrough in favour of
continuous brewing using immobilized yeast could be expected only on achievement of the following process characteristics: simple design, low investment costs, flexible operation, effective process control and good
product quality. The application of cheap carrier materials of by-product origin could significantly lower the investment costs of continuous fermentation systems.
This work deals with a complete continuous beer fermentation system consisting of a main fermentation reactor (gas-lift) and a maturation reactor (packedbed) containing yeast immobilized on spent grains and
corncobs, respectively. The suitability of cheap carrier materials for long-term continuous brewing was proved. It was found that by fine tuning of process
parameters (residence time, aeration) it was possible to adjust the flavour profile of the final product. Consumers considered the continuously fermented beer to be of a regular quality. Analytical and sensorial profiles of both continuously and batch fermented beers were compared.(Fundação de Amparo a Pesquisa do Estado de São Paulo, Brazil (FAPESPFundação para a Ciência e a Tecnologia (FC
Legacy of pre-disturbance spatial pattern determines early structural diversity following severe disturbance in mountain spruce forests in Czech Republic
Background
Severe canopy-removing disturbances are native to many temperate forests and radically
alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity
to ecosystem function after such events. Poorly understood is the degree to which the structural
complexity of an old-growth forest carries over to the next stand. We asked how predisturbance
spatial pattern acts as a legacy to influence post-disturbance stand structure,
and how this legacy influences the structural diversity within the early-seral stand.
Methods
Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe
bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and
dead trees, crown projections, down logs, and herb cover.
Results
Post-disturbance stands were dominated by an advanced regeneration layer present before
the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus
aucuparia), were strongly self-aggregated and also clustered to former canopy trees, predisturbance
snags, stumps and logs, suggesting positive overstory to understory neighbourhood
effects. Thus, although the disturbance dramatically reduced the stand’s height
profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance
stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced
advanced regeneration through microsite and light limitation. Under formerly dense
canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater
heterogeneity in heights
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