Quality of Selected Fruits and Vegetables of North America - American

10

Non-Bitter Hop Contributions to Beer Flavor VAL PEACOCK and MAX DEINZER

Downloaded by UNIV OF PITTSBURGH on May 16, 2016 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0170.ch010

Department of Agricultural Chemistry, Oregon State University, Corvallis, OR 97331

The main purpose of using hops in beer is to add bitterness to the final product. A series of compounds referred to as α and ß-acids are responsible for this taste (1). A secondary, ill defined flavor (flavor referring to smell and taste) is also imparted to beer by brewing with "aroma hops." Not all hop varieties are considered "aroma hops," and there is evidence that the flavors imparted to beer by different aroma hops are different (2). There has been considerable controversy in recent years as to the nature and source of this flavor. Researchers have credited terpene alcohols (2, 3), humulene oxidation products (4, 5), multicyclic terpenoid ethers (6) and carotenoids (6) as being in part responsible for this flavor. Floral Hop Aroma/Taste The most easily definable hop contribution to beer aroma is a floral flavor note that certain hop varieties (not necessarily the traditional "aroma hop" varieties) impart to beer (2). Indications are (Table I) that the floral compounds linalool and geraniol are responsible for this aroma note. Geranyl isobutyrate, though present in the more floral beers, is probably in too low concentration to have a major effect on beer flavor. α-Terpineol is eliminated from consideration for the same reason. Linalool has been reported in beer at an estimated concentration of 34ppb (3) by Lindsay and at a concentration of 470ppb (7) by Tressl. As the current techniques for measuring these trace organics in beer are somewhat dubious, and considering the difficulties different investigators have in agreeing on what the sensory thresholds are for these compounds in beer (8, 9^), i t is hard to say what relative importance to beer hop aroma/taste they have. Clearly linalool must be an important contributor to this aroma/ taste even considering Meilgaard's threshold of 80ppb (8) for this compound in beer. Geraniol seems to be important only in beers brewed with certain hop varieties, whereas linalool is common to a l l the beers and hops investigated. Geraniol in hops 0097-6156/81/0170-0119$05.00/0 © 1981 American Chemical Society Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

e

---

250

100

—

100

250

100

200

75

25

--

75

--

--

200

150

500

150

-50

—

2000

e

b

e

—

500 '

—

—

—

1

10 i n water*

>40,000

36*

--

f

g

450

2000

27ppb

—

1

Threshold i n Beer

--

175

200ppb

25ppb

Hallertauer^ Beer

50

50

200

75

c

a. Commercial beer brewed w i t h 60% Cascade and 40% C l u s t e r hops. b. Commercial beer brewed w i t h a mixture o f European hops. c. A p i l o t brew made by a commercial brewery u s i n g C l u s t e r hops o n l y , d. Same as c , only u s i n g H a l l e r t a u e r hops. e. Ref. No. 4. f . Ref. No. 8. g. Ref. No. 2. h. Ref. No. 6. i . Subsequent analyses showed a t h r e s h o l d o f 2500 ppb.

Humulol

3-Eudesmol

Humulenol I I

δ-Cadinol

T-Cadinol

—

—

Caryolan-l-ol

Nerolidol

—

Humulene Epoxide I

6

50

4,4-Dimethylcrotonolactone 100

100

200

Geraniol

25

---

150

75

200ppb

--

Cluster Beer

—

200ppb

g

75

200ppb

—

European^ Mixture Beer

Isobutyrate*

e

a

Hop O i l Components Found i n Beer

Geranyl

a-Terpineol

Linalool

6

T r a n s - L i n a l o o l oxide

Compound

Cascade Beer

Table I .


10.

PEACOCK AND

DEiNZER

Non-Bitter Hop Contributions to Beer Flavor


I

IV

VII

VIII

X

XI

II

III

V

VI

121

IX

XII

Figure 1. Structures of hop oil components. Key: I, humulene; II, humulene epoxide I; III, humulene epoxide II; IV, humulol; V, humulenol II; VI, humuladienone; VII, a-eudesmol; VIII, β-eudesmol; IX, hop ether; X, karahana ether; XI, β-ionone; and XII, β-damascenone.



122

QUALITY

OF

SELECTED

FRUITS

AND

VEGETABLES

i s v a r i e t a l s p e c i f i c . G e r a n i o l i s b e l i e v e d to be r e s p o n s i b l e f o r the much more i n t e n s e f l o r a l aroma of beers brewed w i t h Cascade hops ( 2 ) . There i s considerable disagreement as to what the sensory t h r e s h o l d of t h i s compound i s i n beer, but both major i n v e s t i g a t o r s (2, 9) r e p o r t that there i s an unusually l a r g e v a r i a t i o n of i n d i v i d u a l t h r e s h o l d s . Many persons (one-third) can perceive g e r a n i o l c o n f i d e n t l y at 25ppb and others cannot detect g e r a n i o l at even a few hundred ppb. To most people g e r a n i o l i s apparently an important aroma/taste c o n t r i b u t o r i n beer. Geranyl i s o b u t y r a t e i s an important f l o r a l hop component as i t i s b e l i e v e d that much of the compound present i n hops i s hydrolyzed to g e r a n i o l , which i s much more f l a v o r a c t i v e , during brewing ( 2 ) . T r a n s e s t e r i f i c a t i o n of hop o i l f a t t y - a c i d methyl e s t e r s to methanol and t h e i r corresponding e t h y l e s t e r s i s b e l i e v e d to take place during fermentation (6, 10). Hydrolysis of t h i s e s t e r during fermentation, t h e r e f o r e , would not be s u r p r i s i n g . The r a t i o of g e r a n i o l to geranyl i s o b u t y r a t e i n Cascadehopped and Cluster-hopped beers (Table I) as compared to t h e i r hop o i l s (Table I I ) tends to support t h i s i d e a . I t has been reported that fermentation of a 6% glucose s o l u t i o n w i t h 50ppm geranyl i s o b u t y r a t e added r e s u l t e d i n the h y d r o l y s i s of 15% of the e s t e r ( 2 ) . Hop storage, wort b o i l i n g and beer aging may r e s u l t i n f u r t h e r h y d r o l y s i s . As a r e s u l t , i t i s the o v e r a l l g e r a n i o l - g e r a n y l i s o b u t y r a t e content of the hop that should be considered as w e l l as the l i n a l o o l content. An attempt has been made to c o r r e l a t e the amount of t h i s f l o r a l f l a v o r one might expect from a beer brewed to the same b i t t e r n e s s l e v e l using d i f f e r e n t hop v a r i e t i e s . The y i e l d of o i l and b i t t e r i n g compounds from the hop was considered i n t h i s c o r r e l a t i o n . Cascade, Shin-shu-wase and Backa were reported as the v a r i e t i e s from which one would expect the most f l o r a l f l a v o r and P e r l e and H a l l e r t a u e r were reported to be low i n f l o r a l f l a v o r p o t e n t i a l (2). " K e t t l e Hop"

or "Noble Hop"

Aroma/Taste

" K e t t l e hop" aroma i s an i l l u s i v e f l a v o r note reminding one of hops, imparted to beer by the vigorous b o i l i n g of "aroma hops" i n the wort f o r up to a few hours. Brewers and hop f l a v o r r e searchers c u r r e n t l y do not agree on the chemical or s e n s o r i a l nature of t h i s f l a v o r note. I t i s commonly described as s p i c y or h e r b a l . There are no standard compounds used to i l l u s t r a t e t h i s f l a v o r note to f l a v o r p a n e l i s t s . This long wort b o i l i n g time i s important i n that most of the mass (80-90%) of t y p i c a l hop o i l i s made up of terpene and s e s q u i terpene hydrocarbons which are e i t h e r steam d i s t i l l e d out of the wort, polymerized or o x i d i z e d to more water s o l u b l e compounds during the process (4, _5, 11, 12). As a r e s u l t , these hydrocarbons are not found i n beer (4_, _5, _7) and t h e r e f o r e are not r e s p o n s i b l e for t h i s f l a v o r . I n v e s t i g a t o r s i n t h i s f i e l d do agree that t h i s


10.

PEACOCK A N D

DEiNZER

Non-Bitter Hop Contributions to Beer Flavor

123

a

Table I I . Beer F l o r a l Aroma/Taste Components i n Hops *

Hop V a r i e t y


Cascade

Linalool

Geraniol

Geranyl I s o b u t y r a t e

.85

.27

1.56

.44

.24

.60

.75

.03

.12

.50

n.d.

n.d.

Hallertauer

.41

n.d.

n.d.

C

.26

n.d.

n.d.

Northern Brewer

.28

.06

.12

Shin-shu-wase

.39

.37

1.08

Cluster

0

c Tettnanger Hersbrucker

Perle

Talisman

.31

.37

.95

Brewer's Gold

.41

Quality of Selected Fruits and Vegetables of North America - American

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