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Feb 20, 2013 (4 years and 5 months ago)

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Rascon, Lucas

Writing 116

Research Review

4/15/2012



Developments in Maintaining and Improving Beer Flavor Stability

Abstract


Production of a high quality beer is of the utmost importance for a brewery if it is to be
successful
. The fermentation process must be carefully monitored and controlled from start to
finish in order
preventing the formation of undesirable flavors. The

organic compounds which
cause undesirable

flavors in

beer
form

not only during the fermentation process

but
also

the

aging
process
beer undergoes while in storage
.

This

review addresses the recent methods of
improving or maintaining beer stability during the fermentation process

and the aging process
.
This is approached on the f
ermentation media level by id
entifying and altering the chemical

composition of wort, as well as

through alterations in brewer
s

yeast
’s physical structure

and its
genome.

Introduction

While the fermentation process remains the central method for conduction fermentation
research
, t
he
development

o
f new analytic techniques along with the

advances in

the biological
sciences
has

provided
new methods for monitoring the fermentation process
of beer and wine
;
H
ybrid e
lectronic tongues
Create

precise chemical imag
e

of

fermenting
which can be
interpreted
as to

how a beer would taste

[5], and
the additional use of polymerase chain reaction (PCR) and
gas chromatography have
also
provided a greater scope for interpreting
chemical

data.
.
W
ith

these new tools and knowledge at our disposal, we now ha
ve a greater understanding of the
significance both yeast and wort play in developing and maintaining proper beer stability and
flavor profiles.


Rascon
2


Moderating
W
ort
C
omposition

and Fermentation Conditions


A major component of flavor balance comes from the
wort composition itself; the wort
gravity and nitrogen levels have a significant effect on yeast performance and the final beer
flavor
. With an increase in wort gravity (usually through the addition of sugars) there is dilution
effect on the nitrogen leve
ls in the form of free amino nitrogen (FAN). Lower FAN levels have
an adverse effect
on yeast performance,
since the lowered nitrogen containing
molecules are necessary for proper yeast
growth and functionality.

In a study
conducted by Hongjie Lei et al
[6
]
,
various
wort gravities and FAN concentrations
were pitched, fermented, and then
analyzed with Headspace Gas
Chromatography, PCR, and mass spectroscopy. Results indicated cell growth rates and growth
numbers decrease in response to a higher gravity or lo
wer nitrogen level (
figure

2). F
ormation of
higher alcohols

necessary for synthesis ester that contribute highly to the final flavor profile are
shown to have the lowest concentration in a high gravity, high nitrogen environment

(table 1)
.


Yeast enzymatic activity
and its Impact on Flavor

Beer itself is complex, with over 800 different
compounds contributing to flavor, aroma, texture, and
stability

[11]
. Among them is the vicinal diketone
diacetyl, which imparts a slick feel and a buttery t
aste.

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3


In an experiment conducted by Suvarna Dasari and Ralf Kolling
[10]
, diacetyl formation is found
to have a linkage with the import of acetohydroxyacid synthase (llv2) into the mitochondria. The
results of their experiment indicated respiratory deficie
nt yeast mutants accumulated high levels
of diacetyl due to high concentrations of a precursor protein in the cytosol. Interestingly enough,
the results of the experiment also indicate that the introduction of an ATP3
-
5 allele into a yeast
strain could hel
p reducing diacetyl levels by raising membrane potential in yeast to facilitate
import of the I
LV
2 precursor protein.

Alterations in Yeast Genome

and Gene Functionality

As previously stated, the chemical composition of beer during fermentation
plays just

as
large a role in

its flavor profile and stability as the final composition
, but modifying yeast itself
to boost efficiency has been met with success.

Sulfites and glutathione provide anti
-
aging effects
to the beer to help maintain its flavor after ferme
ntation, while hydrogen sulfide, for which
sulfite is a precursor molecule (figure 1), imparts a skunk
-
like sulfur aroma.

Tezuka, H

et al. had
conducted research in cloning a gene that could reduce hydrogen sulfide production [2]. Similar
research had also

been conducted by

Yefu Chen et al.

[9]
,

where
U
V

mutagenesis

on yeast cells
as an approach to engineer yeast cells that would produce these sulfur compounds in a desirable
balance

to ultimately

improve flavor stability. As a result, one resulting mutant o
btained showed
a considerable increase

in

SO2 production and decreased H2S production
as

a result of decrease
sulphite reductase activity caused by the UV induced homozygous recessive mutation
; however

the cause can only be speculated, with a possibility o
f transcription and posttranslational changes
on the sulfite reductase genes

[1]
.



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4


Yeast strains can be modified genetically as well, and with dev
elopments in genetic
engineering,
such methods are becoming more viable and are having greater success
.
Such

a
strain is TYRL21

[3]
, which
is
able

to lower residual sugars after fermentation by increasing
glycosidic hydrolysis efficiency by altering gene expression

by plasmid transformation
. TYRL21
has also increased the fermentation rate and
lowered off
-
fla
vor compounds.

Other genetically
altered yeast strains such as TYRL21 have also been produced and are considered safe for
consumption

[4]
.

Conclusions

The research
presented
has shown that there is still much progress to be made

in order to
improve

b
eer

flavor stability to create a higher quality beverage
.

I
t is necessary to approach
fermentation while considering both wort composition and the
a
ffect alterations to yeast strains
will have in terms of viability, performance,
and improved

function.

Further

research
would
provide more significant advances that would appealing to large scale breweries to continue
producing consistent quality beverages with a longer shelf life and lasting flavor.

References


1.

Hansen, J., & Kielland
-
Brandt, M. C. (1996). Inactiv
ation of MET10 in brewer’s yeast
specifically increase SO 2 formation during beer production. Nature Biotechnology, 14,
1587

1591.

2.

Tezuka, H., Mori, T., Okumura, Y., Kitabatake, K., & Tsumura, Y. (1992). Cloning of a
gene suppressing hydrogen sulfide produ
ction by Saccharomyces cerevisiae and its
expression in a brewing yeast. Journal of the American Society of Brewing Chemists, 50,
130

133.

Rascon
5


3.

Wang, J. J., Wang, Z. Y., He, X. P. and Zhang, B. R., Construction of amylolytic
industrial brewing yeast strain with

high glutathione content for manufacturing beer with
improved antistaling capability and flavour. J. Microb. Biotech., 2010, 20,1539
-
1545.

4.

Akada R (2000) Genetically modified industrial yeast ready for application. J Biosci
Bioeng 94:536

544

5.

Kutyła
-
Olesiuk A, Zaborowski M, Prokaryn P, Ciosek P. Monitoring of beer
fermentation based on hybrid electronic tongue. Bioelectrochemistry(0).

6.

Lei H, Zhao H, Yu Z, Zhao M. Effects of wort gravity and nitrogen level on fermentation
performance of Brewer’s

yeast and the formation of flavor volatiles. Applied
Biochemistry and Biotechnology 2012;166(6):1562
-
74.

7.


Olaniran AO, Maharaj YR, Pillay

B. Effects of fermentation temperature on the
composition of beer volatile compounds, organoleptic quality and spent yeast density.
EJB 2011;14(2):5
-
.

8.


Procopio S, Qian F, Becker T. Function and regulation of yeast genes involved in higher
alcohol and est
er metabolism during beverage fermentation. European Food Research
and Technology 2011;233(5):721
-
9.

9.

Chen Y, Yang X, Zhang S, Wang X, Guo C, Guo X, Xiao D. Development
of

saccharomyces cerevisiae

producing higher levels of sulfur dioxide and glutathione to

improve beer flavor stability. Applied Biochemistry and Biotechnology 2012;166(2):402
-
13.

10.

Dasari S, Kölling R. Cytosolic localization of acetohydroxyacid synthase Ilv2 and its
impact on diacetyl formation during beer fermentation. Applied and Environmenta
l
Microbiology February 1, 2011 February 1, 2011;77(3):727
-
31.

11.



-

-
Bermúdez de Castro M, Segura
-
Carretero A, Cruces
-
Blanco C,
Fernández
-
Gutiérrez A. Analysis of beer components by capillary electrophoretic methods.
TrAC Trends i
n Analytical Chemistry 2003 0;22(7):440
-
55.