Post on 24-Aug-2020
IBD Conference, Wellington, 19-23 March 2018
Investigating the factors influencing
hop aroma in beer
Graham Eyres, Tobias Richter, Jamie Scrimgeour,
Pat Silcock and Phil Bremer
Department of Food Science University of Otago, Dunedin, New Zealand
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Outline
• Introduction: Hop aroma in beer
• Research program at University of Otago
– Research objectives
• Study 1: Effect of yeast strain on
hop-derived compounds in beer
• Study 2: Effect of yeast pitch rate
• Study 3: Online measures during
fermentation
• Summary and next steps
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Introduction: Hop Aroma in Beer
• Consumers crave novel aroma and flavour
characters and seeking greater diversity.
• Hop aroma and flavour in beer is a major
driver for this diversity.
– Wide diversity of sensory attributes.
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Introduction: Hop Aroma in Beer
• New aroma cultivars being released
around the world.
– E.g. “Hops with a difference” breeding program
• Selected for novel aroma characters
– But the compounds responsible in beer are not well
characterised.
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Introduction: Hop Aroma in Beer
Hop aroma in beer is not well understood
Opportunity
• Current resurgence of interest in aroma hops and
hop chemistry due to growth of the craft
beer industry.
• Add value to the industry through understanding
of hop aroma in beer.
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Research Objectives
Long term goals
• Understand the aroma compounds responsible for
hop derived aroma in beer.
• Understand the factors that influence hop flavour in
beer.
Current research objective
• Investigate the effect of yeast strain and
fermentation parameters on hop compounds in beer.
Target Outcome: Control and optimise hop flavour in beer
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Study 1: Effect of yeast strain on hop flavour
Research Question What is the effect of yeast strain on hop
volatile compounds in beer?
+ =
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Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Study 1: Effect of yeast strain on
hop-derived compounds in beer
Introduction
• Evidence that yeast strain and fermentation factors
have a dramatic effect on hop flavour in beer.
• Limited information in the literature of these interactions
under controlled conditions.
Hypotheses:
– Adsorption and loss during fermentation
– Biotransformation of hop compounds
– Release of glycosidically bound compounds
– Sensory interactions with fermentation derived compounds
• The fundamental mechanisms and relative magnitude of
these different effects are not well understood.
Beer fermented in 1L bottles
With aroma hops
No aroma hops
Hot water aroma hop extract
Key parameters:
• 10P wort
• 20 IBU (with Waimea)
• 12 day fermentation at
20C
• 5 day maturation
at 2C
• Yeast: US-05
(1x107cell/mL)
GC-
MS
• 90C for
5 min
First Step: Identification of target compounds
Aroma Hop:
Motueka (5g/L)
90C for 5 min
41 Compounds Significantly Differed
Hop-derived positively influenced by fermentation
Hop-derived negatively influenced by fermentation
Yeast-derived positively influenced by hops
Yeast-derived negatively influenced by hops
Hop-derived not influenced
Hot Water Aroma Hop Extract Beer without Aroma Hops Beer with Aroma Hops
130 Compounds Detected
Main Study Design – Yeast Selection
Strain Details
US-05 Fermentis ale strain
S-33 Fermentis ale strain
BE-256 Fermentis ale strain
WB-06 Fermentis wheat beer
OTA 79 Ale strain
WLP045 Scotch whiskey yeast
WLP730 Chardonnay wine yeast
Exotics SPH Anchor Wine yeast hybrid
OTA 48 Schizosaccharomyces pombe
Fermented @ 20C Fermented @ 15C
Strain Details
W-34/70 Fermentis lager strain
S-23 Fermentis lager strain
S-189 Fermentis lager strain
OTA 19 European lager yeast
VIN 13 Anchor Wine yeast hybrid
OTA 29 Champagne yeast, S. bayanus
15 Yeast strains
Methods
• Wort (10P, 20 IBU) Late Hopped with Motueka (5g/L).
• Each strain: 2 fermentation replicates x 2 yeast cultures.
• Headspace sampling in duplicate with Gerstel Twister (PDMS) and
analysed using GC/MS.
Study 1: Preliminary Results PCA of all yeast strains – selected compounds
BE-256
BE-256
Exotics
Exotics
OTA19
OTA19
OTA29
OTA29
OTA48
OTA48
OTA79
OTA79
S-189
S-189
W-34/70 W-34/70
S-23
S-23
S-33
S-33
US-05
US-05
VIN 13
VIN 13
WB-06
WB-06
WLP045
WLP045
WLP730
WLP730
-6
-4
-2
0
2
4
6
8
-6 -4 -2 0 2 4 6 8 10 12
PC
2 (
16 %
)
PC 1 (25 %)
• Spread of differences in volatile
compounds between yeast
strains
• No distinct groups according to
Ale, Lager or wine yeast types
Wheat beer yeast
Champagne Yeast
Chardonnay Yeast
European Lager
-6
-4
-2
0
2
4
6
8
-6 -4 -2 0 2 4 6 8 10 12
PC
2 (
16 %
)
PC 1 (25 %)
myrcene
linalool
terpinen-4-ol
citronellol
citronellol acetate
geraniol
geranyl acetate
nerol
neryl acetate
methyl geranate
Study 1: Preliminary Results PCA of all yeast strains – selected compounds
Ale Yeasts – Selected Compounds
Study 1: Conclusions
• Different yeast strains resulted in a variety of volatile
compound profiles.
• Evidence in differences in biotransformation of hop
derived compounds.
• Expected to have impacts on hop character and intensity
in beer.
– Ongoing research to look at Sensory Evaluation.
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Study 2: Yeast pitch rate on hop compounds in beer
Low Pitch
2 M cells / mL Standard Pitch 10 M cells / mL
High Pitch 50 M cells / mL
Late Hop LH_LP LH_SP LH_HP
No Late Hop NH_SP
Research Question What is the effect of pitch rate on hop
volatile compounds in beer?
• Three pitch rates with
Fermentis SafAle US-05 • Late hopping with
Nelson Sauvin (5g/L)
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Sample preparation and analysis
• Wort (10P, 20 IBU) were fermented at 20C to
constant gravity in EBC fermentation tubes.
• Conditioned at 3C for 10 days.
• Fermentations performed in duplicate.
• Samples taken for volatile analysis using GC/MS
using a headspace SPME method (n=3).
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Fermentation Profiles
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250
YE
AST
CE
LLS
PE
R M
L (M
ILLI
ON
S)
TIME (HOURS)
NH_SP 1 NH_SP 2
LH_LP 1 LH_LP 2
LH_SP 1 LH_SP 2
LH_HP 1 LH_HP 2
0
2
4
6
8
10
12
0 50 100 150 200 250
YE
AST
CE
LLS
PE
R M
L (M
ILLI
ON
S)
TIME (HOURS)
NH_SP 1 NH_SP 2
LH_LP 1 LH_LP 2
LH_SP 1 LH_SP 2
LH_HP 1 LH_HP 2
High Pitch
High Pitch
Std Pitch
Low Pitch
Low Pitch
Std Pitch
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Results
• Fermentation esters decreased with increasing pitch rate.
Low Std High Low Std High No Late
Hop
No Late
Hop
• Significant effects of pitch rate on hop-derived compounds
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Study 2: Conclusions
• Concentrations of hop derived compounds varied
with yeast pitch rate.
• Compounds followed different trends.
– Potential for different hop flavour balance.
• Biotransformation pathways require further
investigation (not clear correlations).
• Large differences in fermentation compounds
(e.g. esters) expected to have an impact on hop
flavour through sensory interactions.
Study 3: Tracking aroma compounds during fermentation
Beer prepared with different treatments
Yeast\Hop No aroma hop
Motueka Hops
Nelson Sauvin Hops
No yeast Control MT NS
California Ale Yeast
CA CA / MT CA / NS
Scottish Ale Yeast
SA SA / MT SA / NS
3 ml fermentation in HS vials
Key parameters: • 10P wort • 20 IBU (with Waimea) • Flame-out hop addition: 5g/L • Pitching: ~1x107cell/mL • Volume: 6 replicates with 3mL • 5 day fermentation at 20°C
PTR-TOF-MS Proton transfer reaction-time of flight-mass spectrometer
Richter et al. (2018) Submitted to Food Research International
Ethyl hexanoate
Note the changes in hop related, yeast related and hop / yeast related compounds over time
0
2
4
6
8
10
12
14
16
18
0 6 12 18 24 30 36 42 48 54 60 66 72 78
concentration
[pptv]
fermentation time [hours]
Scottish Ale with Nelson Sauvin
Scottish Ale with Motueka
Scottish Ale without hop
no yeast/no aroma hops
Motueka without yeast
Nelson Sauvin without yeast
0
2
4
6
8
10
12
14
16
18
0 6 12 18 24 30 36 42 48 54 60 66 72 78
concentration
[pptv]
fermentation time [hours]
California Ale with Nelson Sauvin
California Ale with Motueka
California Ale without hop
Motueka without yeast
Nelson Sauvin without yeast
no yeast/no aroma hops
Octanoic acid / Methyl heptanoate
Scottish Ale Yeast California Ale Yeast
NS NS
MT MT
No yeast Control
m/z 145.121
Tracking Fermentation with PTR-TOF-MS
0
500
1000
1500
2000
2500
0
5
10
15
20
25
30
0 6 12 18 24 30 36 42 48 54 60 66 72 78
Concentration EtOH [ppbv]
Concentration CO2 [au]
Fermentation time [h]
Control CO2
Fermentation CO2
Control EtOH
Fermentation EtOH
0 h 42 h
6 h 48 h
12 h 54 h
18 h 60 h
24 h 66 h
30 h 72 h
36 h 78 h
Volatile profile differentiation: At the start of fermentation is due to the hop cultivar’s characteristics At end of fermentation is due to differences in the metabolism of the yeast strains.
631 m/z total 168 m/z Sign Diff
CO2 and ethanol curves show rates of metabolism and changes in metabolism
Tracking Fermentation with PTR-TOF-MS
-8
-6
-4
-2
0
2
4
6
8
-10 -5 0 5 10 15
PC
3 (
9%
)
PC1 (40%)
California Ale with Motueka
California with Nelson Sauvin
Scottish Ale with Motueka
Scottish Ale with Nelson Sauvin
ms43.017 ms61.027 ms62.030
ms73.063
ms75.042
ms89.057 ms90.061
ms103.073 ms117.090 ms118.093
ms131.105
ms145.122 ms146.125
ms173.153
ms81.068
ms87.078
ms95.084
ms129.126
ms137.132 ms138.135
ms75.077
ms101.094
ms231.974
Loadings
Hop effects and Yeast / Hop interaction effects are evident. Esters and Terpenes are mainly associated with the differences between the beers
Possible to differentiate the beers based on the last 4 time
points (time points 60-78h)
SA
CA
Tracking Fermentation with PTR-TOF-MS
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Study 3: Conclusions
• Volatile generation during fermentation is
complex and a dynamic process.
• PTR-ToF-MS can successfully differentiate and
monitor the change in compounds during
fermentation.
– Including hop derived compounds.
• Real-time monitoring provides temporal
information that will enhance understanding of
the biochemical pathways and chemical
processes occurring during fermentation.
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Ongoing Research
• Continuing to mine data for hop-yeast
interactions.
• Explore biotransformation pathways and
mechanisms for the differences.
• Link to sensory evaluation to determine the
impact on perceived hop flavour and
aroma.
Graham Eyres, Factors Influencing Hop Aroma in Beer, IBD Conference, Wellington, 19-23 March 2018
Summary
• Apply advanced analytical tools to investigate hop
flavour in beer.
– Effect of yeast strain and fermentation.
– Understand changes over time.
• Gain a mechanistic understanding of the hop-yeast
related chemical changes.
• Enable brewers to select and manage yeasts
cultivars to enhance hop aroma in beer.
– Achieve target flavour profile with consistency.
Acknowledgements
• Dr Franco Biasioli, FEMS, San Michele all’Adige
• Tobias Richter acknowledges Emerson’s JP Scholarship to support his studies.
• Jo Pitt (Fermentis) for providing yeast.
• Ron Beatson (Plant and Food Research) and
Doug Donelan (NZ Hops Ltd) for provision of
hop samples.
THANK YOU
Dr Graham Eyres Sensory Science Research Centre Department of Food Science University of Otago Dunedin, New Zealand graham.eyres@otago.ac.nz (03) 479 7661