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The mysterious kettle hop aroma: Sesquiterpene oxidation products as character impact compounds

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Tatiana Praet

on 16 July 2015

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Transcript of The mysterious kettle hop aroma: Sesquiterpene oxidation products as character impact compounds

What is 'kettle hop' aroma ?
Introduction
mashing
wort
boiling
fermentation
Compound classes
Individual volatiles
Lab scale boiling hop essential oil
Increase of perillene, clovene, cadalene and alpha-humulene and beta-caryophyllene oxidation products:
isomerization
and
oxidation

of sesquiterpene hydrocarbons!
Goal: analytical and sensory study of 'kettle' hoppy aroma
Isolation of a SHC fraction (cv. Saaz), boiling and formation of SOP's
↓ of all fractions during boiling, except for spicy fraction (SOP's ↑ ):
Oxidation of SHC's into SOP's during kettle boil!
Huge losses of all compound classes during whirlpool step
Brewing of conventionally hopped lagers (4 hL)
Monitoring hop oil compounds during brewing process
E0= start boiling,
before early kettle hopping
E10= 10 min after early hopping
E20= 20 min after early hopping
E30= 30 min after early hopping
E40= 40 min after early hopping
E50= 50 min after early hopping
E60= 60 min after ealy hopping
L5= 5 min after late hopping
L10= 10 min after late hopping
W0= start whirlpooling
W15= 15 min after start whirlpooling
PW= pitching wort
F1= after 1 day of fermentation
F2= after 2 days of fermentation
F3= after 3 days of fermentation
F4= after 4 days of fermentation
F5= after 5 days of fermentation
F6= after 6 days of fermentation
BF= before filtration
AF= after filtration
Increase spicy fraction=
slow extraction
from hop pellets or
oxidation SHC's
?
Strong indication for
increase SOP's
when early kettle hopping
oxidation products
related to plant
meta-bolism
oxidation
products
HS-SPME-GC-MS analysis for comprehensive profiling SOP fraction
1
2
3
4
8
10
11
14
16
17
19
23
24
25
31
32
34
36
Sensory evaluation
SOP fraction in iso-
alpha bittered
lager beer
Beer brewed on pilot scale (4 hL)
Non-hopped iso-alpha bittered lager beer
Blank beer vs. beer with addition of oxygenated sesquiterpenoid fraction
Sesquiterpene oxidation products are flavour-activity in beer matrix!
5 assessors, duplicate analysis
Regions only detected 2 out of the 10, are not included in 'flavour-active zones'
lab scale boiling of hop oil in simplified model systems

boiling of SHC fraction
analysis commercial kettle hopped lagers
brewing specifically hopped lager beers
lab scale results also applicable in real brewing practice?
FUNDAMENTAL INSIGHTS
BREWING PRACTICE
→ Analytical discrimination unboiled and boiled hop essential oil !
Number of newly formed compounds upon boiling ↑if initial hop oil concentration ↑

Analytical and sensory discrimination between unboiled and boiled hop essential oil

Addition of
boiled hop oil
to iso-alpha-bittered lager beer imparts
'
hoppy
'
and '
spicy
'
notes

Formation of
SOP's
upon
lab scale boiling
of SHC's

Flavour-activity

of the SOP's in lager beer demonstrated

Particular alpha-humulene and beta-caryophyllene derived alcohols highly flavour-active
Formation of SOP's during real
brewing practice

'Early kettle' hopping leads to elevated levels of SOP's (link with herbal/spicy notes?)
Tatiana Praet
, Filip Van Opstaele, Guido Aerts and Luc De Cooman

lagering
early
late
dry
Hop-derived aroma of lager beer, imparted by 'early' addition aroma hops, characterized by 'spicy/herbal' notes
adapted flavour wheel
polyphenols




lupulin glands
acids (soft resins)
hop essential oil
Monoterpene hydrocarbons
Floral fraction

oxygenated monoterpenoids
esters, ketones, alcohols,...
Sesquiterpene hydrocarbons
Spicy fraction
esters, ketones, alcohols,...
oxygenated
sesquiterpenoids (OS)
storage
kettle boil?
oxidation
Early
kettle hop aroma
Modification hop essential oil:
losses by stripping, polymerization, adsorption to trub/yeast (terpene hydrocarbons)
biotransformations (monoterpenoids)
oxidation terpenes
into SOP's during kettle boil? (better solubility)

Use of
(nobel) aroma hops
(high α-humulene level), sometimes aged (higher levels of SOP's!)

GC-MS detection
oxygenated sesquiterpenoids
in beer!


Aroma charachterized by
'spicy/herbal
' notes

correlation
Late
(kettle) hop aroma
Modification hop essential oil:
losses terpenes (whirlpool, fermentation)
less losses of
linalool
(short boiling time)
biotransformations monoterpene alcohols
formation
geraniol
by hydrolysis geranyl esters
recuction geraniol into
citronellol

Aroma charachterized by
'floral' and 'citrus'
notes

Dry
hop aroma
Direct transfer hop oil compounds
oxygenated fraction (linalool as marker)
terpenes
methylketones and methylesters

Limited modification hop essential oil (ageing)

Aroma charachterized by
'resinous'
and
'fruity'
notes, reminiscent of hop aroma

GC-MS profile hop-derived volatiles in beer similar to profile hop essential oil

Difference in
volatile profile
of unboiled and
boiled hop essential oil
? (quantitative/qualitative)

Oxidation of sesquiterpene hydrocarbons
into sesquiterpene oxidation procuts (SOP's) during boiling?

Are these SOP's also
found in beer
?

Which SOP's are
flavour-active
and could contribute to kettle hop aroma?

Development 'kettle hop' aroma
during brewing process?
Comparison unboiled hop essential oil and boiled hop essential oil (cv Saaz)

boiling process: lab scale, closed system, water
HS-SPME GC-MS analysis
Constant concentration
4 boiled and 4 unboiled hop oil samples
Lab scale
Real brewing
practice

Analysis kettle hopped lagers
Enrichment oxygenated sesquiterpenoids in 3 commercial lagers
SPE fractionation
(Tentative)
identification of volatiles
in spicy fraction of 70% and 80% ethanol sample
Identification new compounds in beer
Detection of 63 volatiles in spicy fraction !
41 tentatively identified
33 oxygenated sesquiterpenoids
New compounds:
iso-korajol
4S-dihydrocaryophyllene-5-one
6(5→4)-abeo-8,12-cyclo-caryophyllan-5-al
6(5→4)-abeo-caryophyll-8(13)-en-5-al
Sensory evaluation boiled hop oil (1000 ppm) in beer (1ppm)
Addition of boiled hop essential oil to non-aromatized iso-alpha bittered lager beer:
'hoppy' and 'spicy' notes ↑
Discrimination
unboiled and boiled hop
essential oil (multivariate statistics)
And what about boiling in wort? And other varieties?
Calibration line
:
recovery
(boiled hop oil vs. unboiled hop oil)
as a function of hop oil concentration
(10, 100, 500, 1000, 5000, 10 000 ppm)
Marker compounds
unboiled and boiled hop oil:
Qualitative differences
boiled hop oil (10, 100, 500, 1000 ppm) vs unboiled hop oil (10 ppm)
→ Inrease in spicy fraction upon boiling due to formation of alpha-humulene and beta-caryophyllene oxidation products and derivatives !
Boiling of increasing
concentrations of hop oil
10 g/L
Recovery oxygenated sesquiterpenoids (incl. SOP's)↑ upon boiling if initial hop oil concentration ↑
Oxidation SHC's
Boiling total hop oil
Discrimination
Chromatogram 90% ethanol
fraction
=SHC fraction
SPE
fractionation
total hop
oil
SPE
fractionation
Hydro distillation
for extraction hop
oil from Saaz pellets
HS-SPME-GC-MS analysis
fractions
Boiling SHC
fraction (1 g/L)
GC-FID for determination
concentration
HS-SPME-GC-MS analysis
fractions
Fraction eluting with 70% ethanol = SOP fraction
Proof for formation of α-humulene and β-caryophyllene oxidation products upon boiling
GC-O for determination flavour-active SOP's
2 highly flavour-active zones, expressing
cedarwood
aroma characteristics
Detection frequencies (/10) flavour active zones
Humulene and caryophyllene derivatives in flavour-active zones:
GC-O for determination
flavour-active compounds in spicy fractions
of a
commercial kettle hopped lager beer
Detection frequency (out of 6 analyses)
SOP's in flavour-active zones of lager beer !
The mysterious 'kettle hop' aroma:
Sesquiterpene oxidation products as character impact compounds

Formation of new compounds

Rearrangement of SHC's

No increase in levels of plant metabolism-related oxygenated sesquiterpenoids

Oxidation of SHC's into SOP's
Lab scale boiling experiments

Kettle boil of brewing practice
Changes in the hop oil-derived volatile profile upon boiling
Caryophyllene and humulene derived (allylic) alcohols in flavour-active zones
Conclusions
Early kettle hopped lager beer (cv. Saaz)
Brew trials
Acknowledgements
Colleagues lab Enzyme, Fermentation and Brewing Technology
Start boiling versus end boiling: compounds characterized by an increase in their level
Increase in wort derived compounds
Increase in SOP's
Full transcript