Further Studies on the Impact of Commercial Malting and Brewing ...

<strong>Further</strong> <strong>Studies</strong> on the Impact of Commercial Malting and Brewing
Practices on Beer Flavour Stability
Aldo Lentini 1 , Ralph Nischwitz 2 , Paul Rigoni 2 , Mark Goldsmith 1 , David Duan 1 ,
Louise Fogarty 1 and Peter Rogers 1
1. Foster’s Group Ltd., Australia
2. Barrett Burston Malting Co. Pty. Ltd., Australia
Key Words
Beer, Malt, Flavour Stability, Antioxidants, Free Radicals, Process Effects, Lipoxygenase
ABSTRACT
Small scale and commercial malting and brewing techniques were utilized to investigate the
effect of raw materials and process conditions on the flavour stability of beer. Stability was
measured using a number of common analytical tests including reactive oxygen species by
ESR, carbonyls by TBA, total polyphenols by direct analysis, anti-radical potential by
DPPH and total thiol proteins, as well as sensory assessment. In this study we observed
that: Malting conditions can be manipulated to alter LOX, however no clear correlation
between the level of LOX and flavour stability parameters was found. Malts produced with
higher kilning temperatures and beers produced using an IOB style of mash give more
flavour stability. Supplementing malts with sugar syrups and removing trub from wort also
improves flavour stability. Adding antioxidants to the mash can improve stability and as
expected higher total pack oxygen combined with higher pasteurisation levels significantly
accelerates the deterioration of beer.
INTRODUCTION
Beer staling 6,7,23,32 has been the topic of numerous studies with emphasis on developing
appropriate systems and processes to improve the overall flavour stability of packaged beer
products 4,8,15,17,25-28 . Beer staling is complex because it involves not only many integrated
pathways, some biological and some chemical, but also because events occurring during
wort production and beer fermentation involve both enzymic and non-enzymic pathways.
There are a myriad of compounds that can potentially contribute to oxidised and stale
flavour notes. Some may contribute more than others. Various unsaturated carbonyl
compounds are thought to be key indicators of aged or stale flavours in beer 7,8,9,23 .
Reactive Oxygen Species (ROS), free radicals derived from molecular oxygen 19,21,23,31,33
are the major contributor to the oxidative damage of beer 7,23,30,31,33 . These radicals are
produced by the reduction of molecular oxygen (itself not particularly reactive) to
superoxide, then to peroxide and finally to the hydroxyl radical 21,23,31,33 . This can occur
throughout the brewing process as well as in the final packaged product. The accumulation
of ROS is dependent on endogenous levels of antioxidants (e.g.. polyphenols, sulphites and
other reductones) and also the levels of quenching agents. 4,14,25,29 .
Flavour stability and beer staling are complex processes involving a multitude of interactive
components. In our previous study we examined the influence of barley variety and malting
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process conditions on lipoxygenase (LOX) and flavour stability parameters and
investigated how brewing conditions influence beer flavour stability. From our previous
investigation 24 we concluded that:
• Barley varieties differ in their LOX potentials.
• Malting process conditions can be manipulated to reduce LOX, but care needs to be
taken as this may affect other malt quality parameters.
• Beer flavour stability indicators cannot be predicted solely from LOX or routine malt
analysis. This was demonstrated by using combinations of micromalting and commercial
malting with small scale and commercial brewing.
• The source and quality of malt used to produce beer does affect flavour stability,
however no clear parameters were able to demonstrate this relationship.
In the following study we continue our investigation into malting process and brewhouse
practice to further our understanding of their effect on beer flavour stability.
Using a small scale brewing procedure we investigated the effect of:
• different micromalting conditions
• different malt types and malt from different commercial malthouses
• IOB compared to EBC style of mashing
• malt to adjunct ratio and adjunct type
• the level of trub in the wort
• adding antioxidants to the mash
Flavour stability indicators of commercial beers from two breweries supplied by three
malthouses were compared and the effect of pasteurization and oxygen were also examined.
MATERIALS AND METHODS
Malt analysis:
Moisture and grain protein were assessed using a FOSS Infratec 1241 whole grain NIR
analyzer. Malt extract, colour, and soluble nitrogen were determined by both the EBC and
IOB methods of analysis (EBC Analytica 1998 and IOB Methods of Analysis 1997).
Diastatic power was determined according to Skalar method No Catnr. 308 – 406 issue
090298/MH/9820512. Wort ß-glucan was determined on the respective IOB and EBC
worts by Segmented Flow Analysis - Skalar method 349-202 issue 041404\EK\99229386.
Malt attenuation was determined on EBC worts using a modified version of the EBC
method 4.11.1
Lipoxygenase (LOX) measurement was based on the method used by Araki 3 , which is a
version of the method based on Baxter 12 , where an extract of malt containing LOX is added
to a linoleic acid substrate and subsequent absorbance change at 234 nm is monitored.
Units are expressed as the change in abs 234 nm/min/gram.
Micro-malting
All samples were screened using a 2.2 mm screen and malted in a Joe White Micromalter
under the following conditions:
Sample size 170 or 800 grams
Steeping Standard steep 8 hrs immersion, 10 hrs air rest, 9 hrs immersion, 17°C
Short steep 6 hrs immersion, 8 hrs air rest, 7 hours immersion, 19°C
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Germination 94 hours at 15°C
Kilning Standard kiln 21 hours, 50 - 80°C
Soft kiln 18 hours, 65 - 75°C
Hard kiln 23 hours, 50 - 90°C
Water was applied 24 hours after the end of steeping to target a maximum of 44 % green
malt moisture.
Commercial malt data
The commercial malts used to assess LOX levels were batch samples of Gairdner, produced
in a number of different malthouses.
The commercial malts used for small scale brewing were batch samples of Gairdner barley
processed at three different malthouses. The different malthouses represented malting
equipment varying in terms of capacity as well as steeping and germination vessel design.
Brewing conditions
All Brewing trials were conducted in triplicate using the brewing procedures listed below.
(a) - Wort Mashing: All fermentation studies were undertaken using sterile high gravity
wort (14 °P) made from 100% malt. Worts were produced using either an IOB style mash
program or an EBC style mash program as follows:
IOB program
• 65°C for 20 minutes
• increased at 1°C /min to 74°C
• hold at 74°C for 10 minutes
EBC program
• 45°C for 20 minutes
• increased at 1°C /min to 55°C
• hold for 15 minutes
• increased to 65°C at 1°C /min
• hold for 20 minutes
• increased to 74°C at 1°C /min
• hold for a final 10 minutes
The mash was lautered and sparged with 76°C hot water. The collected wort was boiled for
60 minutes and cooled to approximately 10°C. The final gravity of the wort was adjusted
to 14°P.
(b) - Fermentation: The 14°P wort was attemperated to 11°C and aerated to approximately
8 mg/L oxygen. The wort was then pitched with lager yeast (a strain of Saccharomyces
cerevisiae) at a rate of 15 x 10 6 cells/mL. Zinc acetate was added at a rate of 0.25 mg/L of
zinc ion. The fermentation temperature was allowed to reach a maximum of 18°C.
Beer analysis:
All laboratory scale beers were analysed after 5 days at 4°C. Total sulphur dioxide in beer
was determined by the published method of the ASBC 1 . The total polyphenol content was
determined by a modified ASBC method 2 .
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Electron spin resonance (ESR):
The estimation of the hydroxyl radical and anti-oxidant values was performed using a
Bruker “E-Scan”, an Electron Spin Resonance instrument (model E240-3000/4000, Bruker
Analytik GmbH, Rheinstetten, DBU), equipped with an auto-sampler, a heating block and a
Gibson auto-pump system (for continuous sampling). The Bruker Win-EPR Acquisition
software, version 4.20 with incorporated Lag-Time analysis software, version 1.09 was
used for data processing 11 .
ESR - PBN test: (for Ea and RGA analysis)
Sample preparation: Beer samples were degassed by filtration (Whatman 2V filter paper,
Whatman Plc., Maidstone, GBR) and a 4.75 mL aliquot of beer transferred into a brown
coloured 15 mL sample vial to which 0.25 mL of 1M N-tert-butyl-a-phenylnitrone (PBN,
Sigma-Aldrich Pty. Ltd., Sydney, Australia) in 96% ethanol was added. Concurrently a
standard consisting of a mixture of 9.9 mL distilled water and 0.1 mL of 0.1M 4-hydroxy
2,2,6,6 tetramethyl piperidin-1-oxyl (TEMPO, Sigma-Aldrich Pty. Ltd., Sydney, Australia)
dissolved in distilled water, was also measured in a separate sample vial. Samples were
then placed in the auto-sampler (within a heat block) and heated to 60°C. The sample was
analysed at 1 min intervals.
Endogenous Anti-oxidant Activity measure (Ea): The endogenous anti-oxidant activity
value (or lag-time) was determined by the method previously reported by Uchida 31,32 .
Radical Generation Activity (RGA): The anti radical activity value was determined
essentially by the method previously reported by Uchida 34 and Torline 30 . The method is
also sometimes quoted as the T150 measurement 30 . The T150 is the measured signal
intensity at 150 minutes into the spectral ESR-PBN analysis.
DPPH test: (for anti-radical potential (ARP) analysis)
Sample Preparation: A stock solution of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) (Sigma-
Aldrich Pty. Ltd., Sydney, Australia) was prepared based on the procedure stated by
Kaneda 22 . The DPPH (1.86x10 -4 mol/L) reagent was prepared by mixing 1 volume of 0.1M
acetate buffer (pH 4.3) with 2 volumes of 96% ethanol (AR).
Anti-Radical Potential (ARP) Measurement: To determine the ARP of a beer, the analysis
was undertaken using the method previously described by Franz and Back 16 . A Bruker “E-
Spin” ESR instrument was used to measure the signal after the beer sample was added to
the DPPH reagent (Beer:DPPH ratio of 1:15 vol/vol) at 20°C.
The initial signal intensity of DPPH radicals (no beer) was measured at time 0 min. The
mixture (beer and DPPH) was prepared and shaken for a few seconds. The mixture was
then measured with the ESR instrument at 1 min intervals for 10 min. The level of DPPH
radicals measured within the sample was expressed as a percentage. To evaluate the ARP,
the area above the plotted sample curve was calculated. The ARP indicates the amount of
reduced DPPH and the reaction rate. The ARP is calculated as; [ARP = 1000 – area beyond
the curve line] and then reported as a percentage value.
Total thiols determination:
The total thiols content of beer was measured using the DTNB assay previously described
by Jocelyn 20 .
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2-thiobarbituric acid (TBA) number analysis:
2-thiobarbituric acid (TBA) was used as an indication of beer oxidation as described by
Grigsby and Palamand 18 . The method measures the interaction of TBA to certain carbonyl
compounds in the beer.
Anti-oxidant addition to the mash:
Various anti-oxidants were added to the brewing mash liquor prior to the addition of grist
in small scale brewing trials using 100% malt as described in the method section. The antioxidants
used were sodium metabisulphite (10 ppm), Tanal B (30 ppm) and sodium
ascorbate (25 ppm). Antioxidants were added to the mash either individually or in
combination. Tanal B is a refined Gallotannin supplied by Omnichem, Belgium.
RESULTS AND DISCUSSION:
Descriptions of flavour stability analytical parameters:
Endogenous Antioxidant (Ea):
Ea is the time elapsed before hydroxyl radicals are detected during forced ageing of beer
samples at 60 °C. The higher the Ea value the greater the endogenous antioxidant activity
and potentially the more robust the beer.
Radical Generation Activity (RGA):
The RGA value represents the level of hydroxyl free radicals generated after force testing
beer at 60 °C for 150 minutes. Beers that exhibit high RGA’s show poor flavour
stability 30,34 .
Anti-radical Potential (ARP):
The ARP value measures the ability of a beer sample to reduce DPPH. A high value
indicates higher levels of antioxidants. The ARP values generally reflect the total
polyphenol content of a beer.
Total Thiols:
Beers contain reactive thiol groups associated with high and low molecular weight proteins,
as well as small peptides. The most reactive thiols, those that are most readily oxidized, are
associated with low molecular weight proteins and peptides (MW

most sophisticated analytical measure of beer oxidation 10 (compared to CG/MS quantitative
and qualitative analysis of individual carbonyl compounds) it is quick and simple to
perform, and gives reliable beer oxidation trends as well as mirroring 5-hydroxymethyl
furfural (5-HMF) content.
Initial and forced TBA numbers were measured. The initial value gives an indication of the
level of free carbonyls in beer, whilst the forced sample gives an indication of the potential
carbonyl content of a beer.
PART I - Small scale brewing studies
Micro maltings:
Using a single batch of Gairdner barley, malts were produced with a wide range of KI,
colour, LOX and DP by manipulating steeping, germination and kilning conditions, Table I.
Mild kilning produced malt with higher LOX and high kilning gave lower LOX.
Table I
Micromalting data – Gairdner barley malted using different programs.
Malts
Standard
program
Short steep at
19°C,
standard
germ and kiln
Standard
steep and
germ with
extra 2 hrs
kilning 90°C
Standard
program with
higher
moisture and
GA3 addition
Standard
steep and
germ with
mild kilning
to 75°C
Peak
germ
moist
%
Malt
Moist
%
EBC
extract
% db
Col
°EBC
KI
AAL
%
DP
°WK
LOX
45.4 3.7 82.1 4.1 46 81.3 372 16.8
43.8 3.6 82.2 4.4 47 81.7 313 12.5
44.3 3.1 82.2 5.4 51 81.6 341 7.6
45.3 3.4 82.7 5.5 54 83.2 380 15.6
44.1 4.0 82.4 4.0 51 82.7 435 18.6
Beer flavour stability results (Table II) indicate that manipulating malting conditions does
have a subtle effect on beer flavour stability parameters. Ea, ARP and polyphenol values
were similar, however there appeared to be differences in thiols and TBA. As previously
found, there is no clear correlation between LOX and the other stability parameters. These
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esults do not appear to demonstrate a malting process that provides a clear advantage for
beer flavour stability.
Table II
Flavour stability results of beer produced using Gairdner barley micromalted using
different programs
Malts
Standard
program
Short steep
at 19°C,
standard
germ and
kiln
Standard
steep and
germ but
extra 2 hrs
kilning
90°C
Standard
program
with higher
moisture
and GA3
addition
Standard
steep and
germ with
mild kilning
to 75°C
Ea
(min)
RGA
(Level
x10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
Total
Thiols
(uM)
TBA
Initial
Number
450nm
TBA
Forced
Number
450nm
LOX
60 80 50 144 19 0.79 1.57 16.8
55 47 66 191 42 0.64 1.56 12.5
61 57 65 194 19 0.93 2.23 7.6
53 72 61 216 25 0.90 2.57 15.6
63 60 58 209 21 0.53 1.50 18.6
Commercial Malting - Evaluation of different Malthouse:
A series of all malt small scale brews were carried out using Gairdner malt from three
different malting plants under IOB type mashing conditions. At least 6 samples per site
were tested. The beers were fermented under standard conditions and then subjected to
flavour stability analysis. All beers were standardised to 5% alcohol and contained similar
levels of natural SO 2 . No SO 2 additions were made.
Although Gairdner barley was sourced from different parts of Australia, the three malting
plants produced malts generally of similar quality, Table III. However, some differentiation
was observed with respect to the extract and soluble nitrogen level produced from the
higher protein barley at Maltings C and the higher LOX result from Maltings B. It is
noteworthy that LOX did not correlate with any process parameters or malt quality
parameters other than EBC colour, which showed an inverse relationship.
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Table III
Malting data from three commercial malthouses
Malts EBC Col TN SN KI Visc AAL WBG DP LOX
EXT °EBC % % mPA.s % mg/L IOB
Maltings A 81.9 3.6 1.75 0.75 43.3 1.55 79.2 132 84 16.3
Mean
SD 0.87 0.37 0.09 0.05 3.6 0.03 0.78 30 9.0 3.5
Maltings B 81.5 3.8 1.76 0.71 40.5 1.50 78.8 122 85 24.1
Mean
SD 0.40 0.15 0.05 0.03 1.2 0.03 0.71 23 10.4 4.0
Maltings C 80.0 4.1 1.87 0.80 43.0 1.51 79.4 105 92 18.1
Mean
SD 0.32 0.57 0.03 0.04 2.3 0.03 0.84 10 5.2 5.0
The associated flavour stability results (Table IV) from the small scale brews show a wider
range of values than the malting data would suggest. The results indicate that the beer
produced from Maltings C has a greater staling potential relative to malts sourced from
Maltings A & B.
The beer produced from malt sourced from Maltings C yielded significantly lower Ea, and
higher initial and forced TBA. Although the highest RGA level and lowest total thiols is
associated with the beer produced from Maltings C, the differences are likely to be too
small to suggest that these alone would make a major contribution to the higher staling
potential of Maltings C. SO 2 levels were very similar for all beers at about 8 ppm and so
cannot explain the differences in the observed flavour stability potential.
Malts
Table IV
Flavour stability results of beer (small scale brews) produced
from three commercial Malthouses
Ea
(min)
RGA
(Level
x10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
Total
Thiols
(uM)
TBA
Initial
Number
450nm
TBA
Forced
Number
450nm
LOX
Maltings A 83 45 53 132 26 0.75 1.68 16.3
Maltings B 79 50 50 153 9 0.68 1.46 24.1
Maltings C 49 59 57 138 6 0.90 2.21 18.1
Impact of malt type and mash program on beer flavour stability:
In this section we investigate the effect malting conditions may have on beer flavour
stability by examining commercial batches of malt produced for sugar adjunct brewing
compared to batches produced for starch adjunct brewing. The malts for this study were
produced at the same maltings.
Malt for sugar adjunct brewing consisted of an 80:20 Schooner/Gairdner blend, whilst the
malt for starch adjunct brewing was 100% Gairdner. Sugar adjunct brewing requires less
diastatic enzymes for production of fermentable sugars and consequently a higher
8

temperature kilning program is used compared to malt for starch adjunct brewing where
there is less tendency for malt enzymes to be denatured. The data (Table V) clearly shows
a difference in DP, AAL and LOX between the two malts, which can be attributed to both
varietal and processing differences.
Table V
Malt analysis of domestic and export malts
Malt
Type
Sugar
brewing
Starch
brewing
EBC
EXT
EBC
Col
TN
%
SN
%
KI Visc
mPA.s
AAL WBG DP LOX
79.8 4.3 1.81 0.79 44 1.50 78.4 144 71 9.0
82.1 3.9 1.78 0.76 43 1.53 81.4 108 90 25.5
In our previous study 28 we found that beers produced with the IOB mash program appeared
to have a higher degree of flavour stability compared to those produced with an EBC style
mash. We repeated these trials using both the malt produced for sugar brewing and the malt
produced for starch brewing. All wort types were fermented under identical conditions and
the resultant beers were standardised to 5% alcohol. Once again the beers contained a
similar level of SO 2 (approximately 8 mg/L) and no SO 2 additions were made.
Table VI
The effect of malt type and mash program on beer flavour stability
Mashing
Program
Style
Sugar
blend
IOB
Starch
blend
IOB
Sugar
blend
EBC
Starch
blend
EBC
Ea
(min)
RGA
(Level
x10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
Total
Thiols
(uM)
TBA
Initial
Number
450 nm
TBA
Forced
Number
450 nm
74 84 55 144 23 0.78 1.57
28 82 55 138 21 0.66 1.50
37 111 49 122 27 0.88 1.56
20 130 50 155 18 0.85 1.84
Analysis of the beers (Table VI) showed some interesting results. IOB style beer was better
compared to the EBC style beer in terms of Ea and RGA values, however the EA value for
the IOB starch blend was the exception. The lower RGA value of the IOB beers shows that
less free radicals are generated once all the endogenous anti-oxidant material is exhausted.
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This indicates that in the long term the IOB beer may have better flavour stability than the
EBC beer.
Table VI data also suggests that irrespective of the type of mashing program used for wort
production (IOB or EBC), the use of malt produced for sugar brewing gives more
favourable results in terms of beer flavour stability compared to malt produced for starch
brewing.
Influence of Adjuncts:
All previous brewing trials were undertaken using 100% malt. As a significant number of
breweries around the world also utilize adjuncts it was decided to look at the effect of
adjunct brewing on beer flavour stability. A malt to adjunct ratio of 60:40 using maltose
(BLM) and sucrose (BLS) syrups were examined.
The data is summarized in Table VII. The beers containing adjuncts (hence less malt)
generally achieved more favourable flavour stability results. Beer made using sucrose
adjuncts produced the highest Ea values, lower RGA and TBA numbers compared to both
maltose syrup based beers and all malt beers. The ESR results would suggest that the
adjunct beers contained less free radicals and more endogenous anti-oxidant material,
whilst the lower TBA results would reflect the lower level of carbonyl precursors (ie. fatty
acids ) than would be found in an all malt beer. The difference between sucrose and
maltose based syrups on flavour stability is still be fully understood.
The all malt beers did contain the highest level of protein thiols and ARP numbers (a
reflection of higher total protein and polyphenols associated with beers containing higher
malt content). This would suggest that the all malt beers may still have the ability to
maintain a degree of protection against free radicals via their protein thiols and polyphenol
composition.
Table VII
The effect of brewing adjuncts on beer flavour stability
Adjunct
Type
100%
Malt
40%
Sucrose
40%
Maltose
Ea
(min)
RGA
(Level
x10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
Total
Thiols
(uM)
TBA
Initial
Number
450 nm
TBA
Forced
Number
450 nm
70 80 55 144 23 0.79 1.57
89 28 36 86 18 0.52 1.43
63 39 40 126 14 0.59 1.58
Influence of Trub:
We also tested the effect of trub on beer flavour stability. Trub consists of polyphenols,
proteins, fatty acids (potential aldedydes) and other organic and inorganic materials.
Polyphenol and protein thiols can protect flavour stability but fatty acids, if broken down to
aldehydes, can create flavour defects. A beer produced by removing trub with
centrifugation was compared to a normal beer. Both brews were 100% malt and brewed
10

using an IOB mash profile. The beers produced had similar analytical parameters in terms
of alcohol and SO 2 .
The results are summarized in Table VIII. Beer produced with low trub gave higher Ea
values and lower RGA numbers, an indication of a higher level of endogenous anti-oxidant
material and suppressed free radical formation. This is also reflected in the lower forced
TBA number for the low trub beer. This would indicate that beers with low trub contained
less aldehydes than the control beer, possibly a reflection of lower free radicals as well as
less fatty acids that can be broken down to aldehydes over time.
Table VIII
The effect of trub level on beer flavour stability
Adjunct
Type
Control
High Trub
Trial
Low Trub
Ea
(min)
RGA
(Level
x10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
Total
Thiols
(uM)
TBA
Initial
Number
450 nm
TBA
Forced
Number
450 nm
47 80 57 163 35 0.68 2.17
60 40 54 102 12 0.67 1.72
Influence of antioxidants added to the mash:
It has been suggested by several researchers 8,36 that one of the most effective ways to
maximize beer flavour stability is to decrease the formation of aldehydes in beer. A major
area of aldehyde formation occurs in the brewhouse. This may be caused by the breakdown
of fatty acids via LOX or chemical pathways. Hence, by minimizing oxidation in the
brewhouse, we should improve the flavour stability of the beer all other conditions being
equal.
A series of pilot scale brewing trials were undertaken adding antioxidants, metabisulphite,
ascorbate and Tanal B, either individually or in combination to the mash.
The data is summarized in Table IX. The addition of any anti-oxidant material either alone
or in combination, appears to have a positive impact on the flavour stability of the beer. In
terms of ESR results, the addition of metabisulphite gave the highest Ea and lowest RGA
value of all the beers tested.
The level of sulphur dioxide in the final beer was shown to be similar for all trial brews.
The antioxidants in consideration show no improvement over metabisulphite alone, so there
are no apparent synergistic effects, suggesting that is discrete.
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Mashing
Program
Style
Table IX
The effect on addition of anti-oxidants into mash during
wort production on beer flavour stability
Ea
(min)
RGA
(Level
x10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
TBA
Initial
Number
450 nm
TBA
Forced
Number
450 nm
Control 56 58 57 162 0.67 1.49
Metabisulphite 80 47 60 141 0.52 1.51
Tanal B 71 54 62 170 0.67 1.66
Metabisulphite
and Tanal B
Metabisulphite,
Tanal B and
Ascorbate
70 52 65 178 0.57 1.48
68 57 69 184 0.49 1.49
PART II Commercial Beer Production
Evaluation of Commercial Brewing:
In order to investigate flavour stability on a commercial scale, beer was assessed in two
breweries supplied from three different maltings. The beers from two Foster’s Australia
breweries were packaged and assessed analytically and organoleptically (after long term
storage) by an expert sensory panel. Brewery A used malt from maltings A whilst, brewery
B obtained its malt from maltings B and C.
Beer analysis (Table X) showed that brewery A consistently gave better values for Ea,
RGA, and TBA compared to brewery B. In terms of aged flavour evaluation (on a scale of
1-8 with 8 being highest flavour quality), beers from brewery A consistently rated between
4 and 5 after 8 weeks of ageing at 30°C, while beers from brewery B were rated between 3
and 4. Although both beers showed aged/oxidized characteristics, the beers made from
brewery A were considered less aged.
It is worth noting that malting A malt in the earlier small scale brews obtained higher Ea
ratings for finished beer ahead of maltings B and C but rated worst for LOX activity in the
malt. We can make no clear distinction between malt and process from these trials.
Table X
Beer flavour stability results for beers produced at 2 different breweries
Ea
(min)
RGA
(Level
x 10 3 )
ARP
(%)
Total
Polyphenol
(mg/L)
TBA
Initial
Number
450 nm
TBA
Forced
Number
450 nm
Brewery A 106 26 50 32 0.67 1.83
Brewery B 85 36 50 31 0.80 1.91
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Influence of pasteurisation and total pack oxygen:
The effect of higher pasteurisation levels and the impact of higher packaged oxygen content
in beer were also investigated. Beers exposed to higher levels of oxygen were double
crown sealed and approximately 1 ppm of air was injected into the bottle (5 times normal
levels). The packaged beers were then subjected to various levels of pasteurisation and
stored at 30°C for over 2 weeks, after which their Ea and RGA values were measured,
Figures 1 and 2 respectively.
Pasteurisation reduces “freshness” this shows up in Ea reduction and an increase in RGA
values. The effect of oxygen addition is slight for the mildly pasteurised beers but
accelerates with severe pasteurisation.
120
100
Normal
Added Oxy
ESR - Ea (min)
80
60
40
20
0
Control (15 PU) 25 PU 50 PU 100 PU
Sample
Figure 1: Impact of pasteurisation and oxygen ingress on Ea values
ESR - RGA (Intensity Level)
50
40
30
20
10
0
Normal Added Oxy
Control (15 PU) 25 PU 50 PU 100 PU
Sample
Figure 2: Impact of pasteurisation and oxygen ingress on RGA Values
13

Table XI lists the flavour rating and aged flavour rating scores. As expected, beers that are
exposed to higher levels of pasteurisation deteriorate and slightly increase in aged
character. Oxygen reduces flavour rating and significantly increases the aged character.
Table XI
Impact on flavour rating and aged flavour (beers stored for 2 weeks at 30°C)
Sample Flavour Rating (1-8) Aged Character (0-5)
Control (15PU) 6 0
25 PU 5.5 0
50 PU 5 1
100 PU 4.5 1
Added Oxy - Control 4 1
Added Oxy - 25 PU 4 2
Added Oxy - 50 PU 3.5 2
Added Oxy – 100 PU 3 3
Notes: Flavour rating: 1 (poor) – 8 (excellent)
Aged rating: 0 (fresh) – 5 (aged)
SUMMARY
The raw materials used to make beer and how they are processed will have an effect on the
many complex mechanisms which cause beer to stale; however the relationship between
them is not always clear. In this study we have used a combination of laboratory and
commercial scale testing and observed the following:
• Beers produced using an IOB style mash program appear to be more stable than
beers from an EBC mash
• Beers produced from worts containing less trub are more stable than beers
containing higher levels of trub
• Beers made with a percentage of adjunct material have a substantial effect on
flavour stability parameters
• Adding antioxidants to the mash improves flavour stability
• Increased pasteurisation and ingress of oxygen significantly decreases beer flavour
stability
A joint approach to optimize both malting and brewing processes will provide the most
effective means of improving beer stability and quality in trade.
ACKNOWLEDGEMENTS
We wish to thank Barrett Burston Malting Co and Foster’s Group for their support of this
work and permission to publish.
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