Objective Measurements of the Flavor Quality of Beer - ACS Publications

7 Objective Measurements of the Flavor Quality of Beer R. C. LINDSAY

Downloaded by UCSF LIB CKM RSCS MGMT on October 7, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0051.ch007

Department of Food Science, University of Wisconsin, Madison, WI 53706

Beer is consumed principally for its pleasant and satisfying sensory effects. The types of beer available around the world vary quite dramatically in sensory characteristics, but within populations consumers select their products on the basis of a general acceptance of beer flavor, subtle distinctive flavor notes, and an absence of unusual or off-flavors. The key role that flavor plays in product advertising and the fact that beer is a reasonably homogeneous liquid system have made the nature of beer flavor the subject of numerous investigations. Flavor Chemistry of Beer Most of the flavor chemistry literature describing beer flavor per se and the brewing parameters affecting flavors of finished products resides in the journals and publications that directly serve the brewing industry. Literature surveys confined to the usual sources of flavor chemistry articles will indicate a deceptive lack of information on the subject. While an extensive review of the flavor chemistry of beer is beyond the scope of this paper, excellent summaries have been published by Palamand and Hardwick (1) and Meilgaard (2,3). Collective considerations of the beer flavor literature indicate that well over 250 compounds have been characterized and reported for beer. These volatile compounds are derived from ingredients (grains, hops), brewing practices (wort boiling), fermentations (yeast, occasionally bacterial infections), and equilibrium reactions (esterifications, staling processes). As with other food flavors, some difficulties and disagreements have occurred in the assignment of roles for individual compounds in the flavor of beer. Undoubtedly many compounds of significance in beer flavor, particularly flavor defects, remain unrecognized at this time. S t i l l , much progress has been made, and attempts are being made to standardize beer flavor terminology (4). Based on extensive evaluations of quantitative data for 89 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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f l a v o r compounds i n beer and f l a v o r thresholds of i n d i v i d u a l and mixtures of compounds, Meilgaard (2) has proposed a tent a t i v e scheme f o r the r o l e of various beer c o n s t i t u e n t s i n determining the perceived f l a v o r of beer (Table I ) . This c l a s s i f i c a t i o n considers those compounds which g e n e r a l l y cont r i b u t e to aroma, t a s t e , and t a c t u a l sensations, and i t can be concluded that as f u r t h e r information accumulates m o d i f i c a t i o n s w i l l be necessary. The b a s i s f o r c l a s s i f i c a t i o n i n the scheme shown i n Table I i s that of Flavor Units (F.U. = Constant X Concentration/Threshold) or as i t i s sometimes r e f e r r e d to, Odor Units (5) . Compounds placed i n the category of primary f l a v o r constituents are present i n concentrations exceeding 2 F.U., and the removal of any one would cause a d e c i s i v e change i n the character of the product. I t can be noted that only s p e c i a l t y beers i n r e l a t i o n to the usual domestic products and d e f e c t i v e beers contain adequate minor v o l a t i l e f l a v o r components to allow c l a s s i f i c a t i o n i n the primary category. Secondary f l a v o r c o n s t i t u e n t s are those that are present between 0.5 and 2.0 F.U., and c o l l e c t i v e l y these c o n t r i b u t e much of the c h a r a c t e r i s t i c f l a v o r to beer. However, removal of any one would r e s u l t i n only a small change i n f l a v o r . T e r t i a r y f l a v o r c o n s t i t u e n t s are present i n l e v e l s equivalent to between 0.1 and 0.5 F.U., and add subs i d i a r y notes to the f l a v o r of beer. For these compounds, the removal of any one would not produce a p e r c e p t i b l e f l a v o r change. The remaining f l a v o r compounds would f a l l i n t o the category of background f l a v o r c o n s t i t u e n t s (below 0.1 F.U.), and even though a great number of compounds f a l l i n t o t h i s category, Meilgaard (2) estimates that the group accounts f o r l e s s than 30 percent of the o v e r a l l f l a v o r of beer. A n a l y s i s of Beer V o l a t i l e s Most of the c l a s s i c a l procedures f o r the a n a l y s i s of v o l a t i l e s i n foods and beverages have been employed with varying degrees of success f o r the determination of beer f l a v o r compounds (6). More complete recoveries of the e n t i r e spectrum of compounds are achieved by d i s t i l l a t i o n s (7,8), f r e e z e - d r y i n g followed by ether e x t r a c t i o n (9), and continuous l i q u i d - l i q u i d solvent e x t r a c t i o n s (10), but these methods are complex and can e a s i l y lead to the formation of a r t i f a c t s . More r e c e n t l y porous polymer entrainment procedures have been adapted f o r use i n the a n a l y s i s of beer v o l a t i l e s (11,12, 13>14,15), but as yet these techniques have not been g e n e r a l l y a p p l i e d f o r r o u t i n e monitoring of beer f l a v o r s . Wohleb (14) used Poropak Q f o r the entrainment of v o l a t i l e s from beer samples held under s e v e r a l storage c o n d i t i o n s , and subsequently analyzed the i s o l a t e s with glass c a p i l l a r y column gas chromatography. Computer a n a l y s i s of q u a n t i t a t i v e data f o r 54 beer f l a v o r compounds i n d i c a t e d that 11 peaks (mainly esters and alcohols)

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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Flavor

Table I.


1.

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T e n t a t i v e Scheme f o r Role of Constituents i n Determining the F l a v o r of Beer.

a

PRIMARY FLAVOR CONSTITUENTS (Above 2 F.U. ) Ethanol Hop B i t t e r Compounds (e.g., Isohumulone) Carbon Dioxide S p e c i a l t y Beers Hop Aroma Compounds (e.g., Humuladienone) Caramel Flavored Compounds Several E s t e r s & A l c o h o l s (High-Gravity Beers) Short-Chain Acids D e f e c t i v e Beers 2- trans-Nonenal (Oxidized, Stale) D i a c e t y l & 2,3-Pentanedione (Fermentation) Hydrogen S u l f i d e , Dimethyl S u l f i d e and Other S u l f u r Compounds (Fermentation) A c e t i c A c i d (Fermentation) 3- M e t h y l b u t - 2 - e n y l t h i o l (Light-Struck-Hops) Others ( M i c r o b i a l I n f e c t i o n , e t c . )

2.

SECONDARY FLAVOR CONSTITUENTS (Between 0.5 - 2.0 F.U.) Volatiles Banana E s t e r s (e.g., Isoamyl Acetate) Apple E s t e r s (e.g., E t h y l Hexanoate) F u s e l A l c o h o l s (e.g., Isoamyl Alcohol) C , C , C- A l i p h a t i c Acids E£hyl Acefate B u t y r i c and I s o v a l e r i c Acids Phenylacetic Acid Non-Volatiles Polyphenols Various A c i d s , Sugars, Hop Compounds fi

ft

n

B

3.

TERTIARY FLAVOR CONSTITUENTS (Between 0.1 - 0.5 F.U.) 2-Phenethyl Acetate, £-Aminoacetophenone Isovaleraldehyde, Methional, A c e t o i n 4- E t h y l g u a i a c o l , gamma-Valerolactone

4.

BACKGROUND FLAVOR CONSTITUENTS (Below 0.1 F.U.) Remaining F l a v o r Compounds

F l a v o r Units (F.U.) = Constant X From Meilgaard (3) .

Concentration/Threshold.



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v a r i e d s i g n i f i c a n t l y w i t h the temperature of storage. Dravnieks (15) u t i l i z e d Apiezon L on Chromosorb Τ f o r the q u a n t i t a t i v e entrainment of beer aroma c o n s t i t u e n t s and u t i l i z e d these data for demonstrating the u t i l i t y of methods f o r c o r r e l a t i n g sub j e c t i v e and o b j e c t i v e f l a v o r data. However, i n f o r m a t i o n on i d e n t i f i e d samples i n a c t u a l experimental designs was not r e ported. To date l i m i t a t i o n s , i n c l u d i n g polymer s t a b i l i t y , ana l y t i c a l r e p r o d u c i b i l i t y , and a n a l y s i s time, have c o n t r i b u t e d to the l a c k of acceptance of porous polymer entrainment procedures f o r the r o u t i n e a n a l y s i s of beer headspace v o l a t i l e s . Most of the r o u t i n e monitoring of beer aroma c o n s t i t u e n t s i s accomplished through the use of e i t h e r s t a t i c headspace sampling procedures (16,17) or d i r e c t carbon d i s u l f i d e e x t r a c t i o n (18), although d i r e c t beer i n j e c t i o n s have been used to some extent (19). These methods employ packed-column gas chromatog raphy, and the number of compounds (peaks) observed i s q u i t e l i m i t e d (Table I I ) . I t i s p o s s i b l e to observe l a r g e r numbers

Table I I .

V o l a t i l e Compounds i n Beer Determined by Q u a n t i t a t i v e S t a t i c Headspace Sampling and Carbon D i s u l f i d e E x t r a c t i o n Procedures.

Determined By Method Compound

Acetaldehyde E t h y l Acetate Ethanol n-Propanol Isobutanol 2-Methylbutene-2 Isopropyl Acetate E t h y l Propanoate 2-Methyl and 3-Methylbutanol m-Xylene ( I n t e r n a l Standard) Isoamyl Acetate E t h y l Hexanoate E t h y l Octanoate 1-Octanol ( I n t e r n a l Standard) Hexanoic A c i d 2-Phenethanol Octanoic A c i d Decanoic A c i d

S t a t i c Headspace

+ + + + + + + + + + +

-

Carbon

Disulfide

-

+ + + +

+ + + + + + + + +


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of peaks during a n a l y t i c a l runs by simply operating the gas chromatograph at higher s e n s i t i v i t i e s , but t h i s i s u s u a l l y not done because of greater a n a l y t i c a l v a r i a b i l i t i e s observed under these c o n d i t i o n s . Under usual c o n d i t i o n s from 10 to 18 peaks are observed i n a given run f o r the s t a t i c headspace or the carbon d i s u l f i d e e x t r a c t i o n procedures (17>1§)> ~ cepted that some peaks are not i d e n t i f i e d and that others may c o n t a i n more than one compound. S t i l l the data are u s e f u l , and many breweries are equipped f o r automated gas chromatographic a n a l y s i s of production samples of beer. I t can be noted that most v o l a t i l e s detected by the carbon d i s u l f i d e e x t r a c t i o n and headspace sampling techniques are d e r i v e d e i t h e r d i r e c t l y or i n d i r e c t l y from the fermentation (and aging) process (Table I I ) . Therefore, many f l a v o r c o n t r i b u t i o n s a r i s i n g from p r o c e s s i n g steps, i n g r e d i e n t s , and c o n s t i t u e n t i n t e r a c t i o n s ( i . e . , s t a l i n g ) go undetected by these methods of a n a l y s i s .


a

n

d

i t :

i s

a c

Sensory A n a l y s i s of Beer F l a v o r s T r a d i t i o n a l l y , the brewmaster has been delegated n e a r l y absolute a u t h o r i t y f o r the determination and maintenance of f l a v o r q u a l i t y of beer i s s u i n g from the brewery. However, as breweries grew i n s i z e and d i s t r i b u t i o n areas i n c r e a s e d , s h i f t s i n r e s p o n s i b i l i t i e s have occurred to the p o i n t that the brewmaster u s u a l l y r e c e i v e s sensory data from expert corporate panels (20,21) and t r a i n e d or s e l e c t e d panels composed of brewery workers (17,21). Expert panels o f t e n perform some type of d e s c r i p t i v e t e s t f u n c t i o n , but the p r i n c i p a l concern i s q u a l i t y c o n t r o l f o r products r e l e a s e d from the brewery. As a r e s u l t , d i f f e r e n c e t e s t i n g i s u s e f u l f o r monitoring u n i f o r m i t y , and the t r i a n g l e t e s t apparently i s the most widely used type of t a s t e t e s t used by expert and t r a i n e d groups i n the brewing i n d u s t r y (17). Some breweries u t i l i z e q u a n t i t a t i v e d e s c r i p t i v e a n a l y s i s procedures f o r c h a r a c t e r i z i n g beer f l a v o r p r o p e r t i e s , and t h i s approach has been reported to a s s i s t i n determining the degree to which consumers can recognize v a r i a t i o n s i n beer f l a v o r s (21). Since i t has been reported that under l a b o r a t o r y c o n d i t i o n s beer consumption r a t e s i n c r e a s e with hedonic r a t i n g s (22), there i s an increased i n t e r e s t i n r e l a t i n g beer f l a v o r a t t r i b u t e s to consumer preferences f o r products (23). Objective A n a l y s i s of Beer Q u a l i t y In a d d i t i o n to the compounds which comprise the v o l a t i l e aroma f r a c t i o n of beer, there are a great number of p h y s i c a l and chemical parameters which can be measured and u l t i m a t e l y u t i l i z e d i n describing or e v a l u a t i n g beer q u a l i t y (15,24,25,26,27). Included are c l a r i t y , foam head r e t e n t i o n , carbon d i o x i d e , and a i r which r e l a t e d i r e c t l y to q u a l i t y appearance f a c t o r s or which



94

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can i n f l u e n c e appearance i n time. Percent a l c o h o l , r e a l e x t r a c t , pH, t i t r a t a b l e a c i d s , f r e e amino a c i d s , headspace v o l a t i l e s , formol n i t r o g e n , and t r a c e metals are measured and r e f l e c t on the s t a t u s or success of the fermentation. Since the b i t t e r n e s s c o n t r i b u t i o n to the f l a v o r of beer i s p r i n c i p a l l y due to the hop r e s i n components, a s p e c i a l a t t e n t i o n i s paid to the measurement and c o n t r o l of these compounds, p a r t i c u l a r l y humulone and i s o humulone (α-acids) which are r e s p o n s i b l e f o r the major p o r t i o n of the b i t t e r f l a v o r i n beer (28). The l i s t of other analyses i s r a t h e r extensive, and depending upon the requirements of breweries v a r i o u s t e s t s are used to provide information f o r production and q u a l i t y c o n t r o l . Objective Measurements of Beer F l a v o r Q u a l i t y Objective assessments of food q u a l i t y are e s s e n t i a l f o r e s t a b l i s h i n g a b a s i s f o r economic value of foods, but f r e q u e n t l y standards defined by measurements are only roughly r e l a t e d to q u a l i t y (29). Since aroma ( i . e . , f l a v o r ) c o n s t i t u t e s a major p o r t i o n of the o v e r a l l apparent q u a l i t y of foods, considerable e f f o r t has been expended f o r developing means f o r meaningfully using gas chromatographic data i n p r e d i c t i n g sensory q u a l i t y (30,31,32). Although c l a s s i f i c a t i o n of foods based on o b j e c t i v e f l a v o r data appears promising f o r a wide range of commodities (33,34,35,36,37), few a c t u a l instances of a p p l i c a t i o n of t h i s approach are apparent. Several a l t e r n a t i v e s f o r the o b j e c t i v e measurement of beer f l a v o r s and c l a s s i f i c a t i o n of beers have emerged from research i n the brewing i n d u s t r y . The PTPA Method. Hoff and Herwig (17) have reported a method f o r the c o r r e l a t i o n of s t a t i s t i c a l d i f f e r e n c e s or l a c k of s t a t i s t i c a l d i f f e r e n c e s between headspace v o l a t i l e p r o f i l e s of beer samples and the r e s u l t s of the widely-used t r i a n g l e t a s t e t e s t s f o r the same beers. A s t a t i c headspace a n a l y s i s technique employing a Poropak Q column f o r s e p a r a t i o n was used f o r c o l l e c t ing q u a n t i t a t i v e data f o r 12 peaks i n the v o l a t i l e fraction' ( e x c l u s i v e of the peaks f o r ethanol and the i n t e r n a l standard). Data from r e p l i c a t e GC analyses were processed by d i v i d i n g each i n d i v i d u a l raw peak area by the sum of a l l raw peak areas, and then s t a t i s t i c a l l y a n a l y z i n g these data between samples. Thus, the procedure was named the "Percent of the T o t a l Peak Area" (PTPA) method. In the PTPA method, a c h r o n o l o g i c a l l y updated database was used to c a l c u l a t e pooled standard d e v i a t i o n s f o r peak area values to overcome problems a s s o c i a t e d with aberrant values sometimes encountered f o r unexplained reasons or f o r those instances where the GC column c h a r a c t e r i s t i c s change with usage. The database c o n s i s t e d of standard d e v i a t i o n s f o r each peak of 24 previous r e p l i c a t e determinations plus the r e p l i c a t e deter-



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initiation under i n v e s t i g a t i o n . The standard d e v i a t i o n s of the o l d e s t of the 25 former r e p l i c a t e s were e l i m i n a t e d from the database each time a new e n t r y was made. When two beers were compared, the procedure was repeated f o r each. Then a t w o - t a i l e d t - t e s t was performed u s i n g the most recent of the pooled standard d e v i a t i o n s obtained from the database and the mean peak area values obtained from the r e p l i c a t e headspace determinations of the two beers. I f none of the peaks i n the v o l a t i l e p r o f i l e s of the two beers were s i g n i f i c a n t l y d i f f e r e n t at the 0.005 l e v e l , the r e s u l t s of a t r i a n g l e t a s t e panel of the beers were p r e d i c t e d to be i n s i g n i f i c a n t at the 0.05 l e v e l . On the other hand, i f one or more of the peaks i n the v o l a t i l e p r o f i l e s were found s i g n i f i c a n t l y d i f f e r e n t between samples at 0.001 l e v e l , the t r i a n g l e panel were p r e d i c t e d to be s i g n i f i c a n t at the 0.05 l e v e l . When one or more peaks were s i g n i f i c a n t l y d i f f e r e n t between samples at the 0.005 l e v e l , but were i n s i g n i f i c a n t at the 0.001 l e v e l , no p r e d i c t i o n was made and more analyses were r e q u i r e d to r e s o l v e the s i t u a t i o n . In a t e s t of the c o r r e l a t i o n of the PTPA method with t r i a n g l e t a s t e panel r e s u l t s (Table I I I ) , i t was found that the beers i n 32 of 69 comparisons of f r e s h American l a g e r beers were p r e d i c t e d by the PTPA method to give s i g n i f i c a n t l y d i f f e r e n t t r i a n g l e t a s t e panel r e s u l t s . In a c t u a l t r i a n g l e t a s t e panel t e s t i n g , beer samples i n 27 of these comparisons were found to be s i g n i f i c a n t l y d i f f e r e n t while the beers i n 5 of the comparisons were found not s i g n i f i c a n t l y d i f f e r e n t . Conversely, the PTPA method p r e d i c t e d 37 of the 69 comparisons to be not s i g n i f i c a n t l y d i f f e r e n t , and a c t u a l t a s t e panels showed that 35 of these p r e d i c t i o n s were c o r r e c t . Table I I I .

E v a l u a t i o n of C o r r e l a t i o n o f PTPA P r e d i c t i o n s with T r i a n g l e Taste Panel Results f o r Lager Beers.

PTPA P r e d i c t e d T r i a n g l e Panel Results T r i a l s Sig. Different

T r i a l s Not Sig. Different

A c t u a l T r i a n g l e Panel Results (0.05) T r i a l s Sig. Different

T r i a l s Not Sig. Different

32

0

27

5

0

37

2

35

From Hoff and Herwig (17).


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Hoff and Herwig (17) suggested that r o u t i n e t r i a n g l e t a s t e panel t e s t i n g of normal, f r e s h American l a g e r beers could be reduced by e l i m i n a t i n g those samples which were found to be not d i f f e r e n t by the headspace a n a l y s i s procedure. However, i t was noted that the PTPA method would not recognize samples of beers c o n t a i n i n g o r g a n o l e p t i c a l l y detectable l e v e l s of s u l f u r , s t a l i n g , or c e r t a i n hop compounds. Therefore, i t appears that some type of small d e s c r i p t i v e panel should be employed to detect beers e x h i b i t i n g these s i g n i f i c a n t , but unusual l a g e r beer f l a v o r c h a r a c t e r i s t i c s . Discriminant A n a l y s i s of GC V o l a t i l e P r o f i l e Data. The computer i d e n t i f i c a t i o n and c l a s s i f i c a t i o n of some s e l e c t e d beer samples with the a i d of stepwise d i s c r i m i n a n t a n a l y s i s (38) of v o l a t i l e p r o f i l e s from e i t h e r carbon d i s u l f i d e e x t r a c t a b l e s or headspace vapors has been reported by Hoff, Helbert, and Chicoye (39,40). In t h i s work the sensory c h a r a c t e r i s t i c s of i n d i v i d u a l beer samples were not determined, but rather i t was assumed that competitive American l a g e r beers, beers brewed with d i f f e r e n t adjuncts (carbohydrate sources), and beers from branch p l a n t s w i t h i n a company would e x h i b i t f l a v o r d i f f e r e n c e s i f t h e i r v o l a t i l e p r o f i l e s d i f f e r e d . To demonstrate the u t i l i t y of the technique, i n d i v i d u a l l o t s of beer from a given source were d i v i d e d and subsequently analyzed by e i t h e r headspace or carbon d i s u l f i d e e x t r a c t i o n procedures to provide both a "known database and "unknown" beer sample data. 11

In one i n s t a n c e , four competitive American l a g e r beers were c l a s s i f i e d on the b a s i s of the q u a n t i t a t i v e amounts of four peaks (isoamyl a l c o h o l s , i s o b u t a n o l , e t h y l a c e t a t e , and isoamyl acetate) from carbon d i s u l f i d e e x t r a c t a b l e s which were s e l e c t e d by the stepwise d i s c r i m i n a n t a n a l y s i s of the 12 a v a i l able v a r i a b l e s . A c a n o n i c a l p l o t of the beers showed t i g h t groupings of both known and unknown samples w i t h i n sample l o t s . The technique was shown (39) to be u s e f u l f o r c l a s s i f y i n g a l l s e l e c t e d samples i n the study on the b a s i s of headspace or carbon d i s u l f i d e e x t r a c t a b l e v o l a t i l e s , i n c l u d i n g beers brewed with d i f f e r e n t types and amounts of adjuncts. An i n t e r e s t i n g aspect which was a l s o demonstrated was that of s h i f t i n g an o r i g i n a l c l a s s i f i c a t i o n of a beer from a branch p l a n t to that of another p l a n t ' s c l a s s i f i c a t i o n a f t e r a brewing m o d i f i c a t i o n was made. U t i l i z a t i o n o f such techniques could be very u s e f u l i n a s s e s s i n g the u n i f o r m i t y of f l a v o r q u a l i t y , p a r t i c u l a r l y when f l a v o r compounds r e f l e c t i n g fermentation parameters are measured. Discriminant A n a l y s i s of Physicochemical V a r i a b l e s I n c l u d i n g GC V o l a t i l e P r o f i l e Data. Reiner and P i e n d l (41) have demonstrated how d i s c r i m i n a n t a n a l y s i s of 49 physicochemical v a r i a b l e s , i n c l u d i n g carbon d i s u l f i d e e x t r a c t a b l e s , could be used to d i f f e r e n t i a t e types of beer, e.g., l a g e r , p i l s e n e r ,



7.

LINDSAY

Flavor Quality of Beer

97

export, e t c . A modified U n i v e r s i t y of C a l i f o r n i a at Los Angeles BMD07M stepwise d i s c r i m i n a n t a n a l y s i s program (38) was used to s e l e c t v a r i a b l e s from the t o t a l physicochemical data a v a i l a b l e which included q u a n t i t a t i v e information on 14 general beer or brewing parameters, 20 α-amino a c i d s , and 15 metabolic by products from the fermentation process. Selected v a r i a b l e s were then used to demonstrate groupings of beer types i n canoni c a l p l o t s , and attempts were made to determine which p r o p e r t i e s allowed c l e a r d i f f e r e n t i a t i o n of beer samples evaluated. Although v a r y i n g degrees of success i n d i f f e r e n t i a t i o n of beer types on the b a s i s of s e l e c t e d physicochemical v a r i a b l e s was achieved by Reiner and P i e n d l (41), c o r r e c t c l a s s i f i c a t i o n of a l l beers w i t h i n a type was r e a l i z e d only f o r a l t and p i l sener d i e t beers when a l l of the i n i t i a l v a r i a b l e s were u t i l i z e d (Table I V ) . With t h i s approach d i f f i c u l t i e s were s t i l l en countered i n the d i f f e r e n t i a t i o n of the more s i m i l a r f u l l , l i g h t Table IV.

Actual Beer Type L i g h t Lager

C l a s s i f i c a t i o n of Beers on the B a s i s of 14 General Parameters, 20 α-Amino A c i d s , and 15 Metabolic By-Products of Fermentation.

Light Lager

Light Export

C l a s s i f i c a t i o n As Pilsener Alt Lager Beer

Pilsener Diet

30

1

4

0

0

L i g h t Export

0

24

4

0

0

P i l s e n e r Lager

3

4

14

0

0

Alt

0

0

0

17

0

0

0

0

0

12

Beer

P i l s e n e r Diet

From Reiner and P i e n d l (41). type beers ( l i g h t l a g e r , l i g h t export, and p i l s e n e r l a g e r ) . While the a l t beer and p i l s e n e r d i e t beer samples were c h a r a c t e r i z e d by d i s t i n c t p h y s i c a l p r o p e r t i e s , the f u l l , l i g h t beer samples e x h i b i t e d s i m i l a r p h y s i c a l c h a r a c t e r i s t i c s . In order to d i f f e r e n t i a t e the f u l l , l i g h t beer types, i t was necessary to expand the a v a i l a b l e data, and t h i s was done by a l s o u t i l i z i n g the sums of a l i p h a t i c e s t e r s , a l i p h a t i c a l c o h o l s , l a c t a t e s , and the v i c i n a l diketones which were c a l c u l a t e d from the o r i g i n a l physicochemical data. The success


FLAVOR

98

QUALITY:

OBJECTIVE

MEASUREMENT

of the f i n a l d i f f e r e n t i a t i o n i s shown i n Table V. A l l 35 l i g h t l a g e r beers were c o r r e c t l y c l a s s i f i e d , and only one beer i n each of the l i g h t export and p i l s e n e r l a g e r c a t e g o r i e s was m i s c l a s s i f i e d . However, i t was claimed that these samples were a c t u a l l y c o r r e c t l y c l a s s i f i e d , and that e r r o r s i n i n i t i a l l a b e l i n g or c l a s s i f i c a t i o n l e d to the apparent f a l s e c l a s s i f i c a t i o n s .


Table V.

Actual Beer Type L i g h t Lager

C l a s s i f i c a t i o n o f Three Types o f L i g h t , F u l l Beers with I n d i v i d u a l Physicochemical Parameters Plus the Sums o f A l i p h a t i c A l c o h o l s , E s t e r s , L a c t a t e , and V i c i n a l Diketones.

Light Lager

C l a s s i f i c a t i o n As Light Pilsener Export Lager

35

0

0

L i g h t Export

0

27

1

P i l s e n e r Lager

1

0

20

From Reiner and P i e n d l (41). Further a n a l y s i s o f the data showed that l i g h t l a g e r beers were d i f f e r e n t i a t e d from l i g h t export beers by higher o r i g i n a l g r a v i t i e s , s o l u b l e n i t r o g e n , anthocyanogens, malate, l a c t a t e , p r o l i n e , and α-amino-nitrogen contents. P i l s e n e r l a g e r beers contained more b i t t e r substances and anthocyanogens, but l e s s pyruvate and higher a l i p h a t i c a l c o h o l s than pale o r l i g h t l a g e r beers. A l t beers which are h e a v i e r and darker beers were shown to have deeper c o l o r s , more anthocyanogens, g l y c e r o l , malate, c i t r a t e , e s t e r s and higher a l i p h a t i c a l c o h o l s than l i g h t l a g e r beers. P i l s e n e r d i e t beers were c h a r a c t e r i z e d by t h e i r very high l e v e l s o f a t t e n u a t i o n , high ethanol contents, low pyruvate and c i t r a t e contents, and very low v i s c o s i t i e s . I t was suggested by these workers that i n c l u s i o n o f q u a n t i t a t i v e data f o r higher aromatic a l c o h o l s and s u l f u r - c o n t a i n i n g compounds would g r e a t l y f a c i l i t a t e d i f f e r e n t i a t i o n o f beer types. However, methods f o r r o u t i n e a n a l y s i s of these components have not been a v a i l a b l e . Discriminant A n a l y s i s o f F l a v o r P r o f i l e D e s c r i p t o r Data. Some workers have taken the p o s i t i o n that methods f o r developing r e l i a b l e q u a n t i t a t i v e sensory data must be a v a i l a b l e before the p o t e n t i a l usefulness of chemical and instrumental f l a v o r analy s i s data w i l l be r e a l i z e d . Along t h i s l i n e , Brown, Clapperton,



7.

LINDSAY

Flavor

Quality

of

Beer

99

and D a l g l i e s h (42) have shown that beers from d i f f e r e n t geographi c a l l o c a t i o n s (Europe, B r i t a i n , and America) can be successf u l l y c l a s s i f i e d by d i s c r i m i n a n t ( c l u s t e r ) a n a l y s i s of q u a n t i t a t i v e f l a v o r p r o f i l e c h a r a c t e r i s t i c s detected by a q u a l i f i e d panel. In t h i s work approximately 40 d e s c r i p t o r s were b e l i e v e d to adequately d e f i n e the f l a v o r of a l l types of beer, but of these only 27 gave s i g n i f i c a n t scores f o r t y p i c a l , l i g h t l a g e r beers. Average p r o f i l e panel scores f o r the 27 s i g n i f i c a n t sensory c h a r a c t e r i s t i c s were obtained f o r 9 brands of E n g l i s h l a g e r beer, 11 brands of C o n t i n e n t a l European l a g e r beer, and 13 brands of North American beer. D i s c r i m i n a n t a n a l y s i s of these data gave c l u s t e r p l o t s showing very c l o s e groupings of the beers w i t h i n each geographical sampling, and the groups were w e l l - s e p a r a t e d i n space. Discriminant a n a l y s i s was used to reduce the v a r i ables to 12 ( i . e . , burnt, b i t t e r , body, d r y i n g , v i s c o u s , smooth, dimethyl s u l f i d e , cabbagy, h i g h - g r a v i t y f u l l n e s s , warming, t o f f e e - l i k e , and l i v e l i n e s s ) , and using these data much more d i f f u s e c l u s t e r p l o t s were obtained. However, a reasonable degree of c l a s s i f i c a t i o n was s t i l l achieved. Brown, Clapperton and D a l g l i e s h (42) a l s o d i s c u s s e d the p r a c t i c e of producing u s e f u l p r a c t i c a l c o r r e l a t i o n s between sensory and instrumental analyses i n the brewery l a b o r a t o r y without a computer. Examples were discussed where l e v e l s of measured dimethyl s u l f i d e c o r r e l a t e d with sensory scores f o r t h i s compound, and that the type of malt employed d i r e c t l y i n f l u e n c e d the l e v e l s of dimethyl s u l f i d e encountered. Similar simple c o r r e l a t i o n s have been u t i l i z e d f o r other compounds causing o f f - f l a v o r s i n beer, and included are d i a c e t y l ( b u t t e r m i l k - l i k e ) , t-2-nonenal (cardboardy, o x i d i z e d ) , and c e r t a i n short-chain f a t t y a c i d s (soapy). Discriminant A n a l y s i s of A n a l y t i c a l (Including GC) and Sensory Data. Research i n t h i s category involves the demonstrat i o n of d i f f e r e n t i a t i o n of beers on the b a s i s of e i t h e r analyt i c a l measurements or sensory data, and then subsequent c l a s s i f i c a t i o n of the beers in the other set of data whichever the case may be. D i s c r i m i n a n t a n a l y s i s can then be used to reduce the number of v a r i a b l e s to those e s s e n t i a l to e f f e c t c o r r e c t classifications. M o l l e_t a l . (43) have used t h i s approach to study the f e a s i b i l i t y of c l a s s i f y i n g beers i n t o c a t e g o r i e s of good, average, or poor as determined by expert t a s t e r s . The expert panel f i r s t scored 10 f l a v o r and aroma c h a r a c t e r i s t i c s and the o v e r a l l f l a v o r impression f o r 34 beers produced under d i f f e r i n g brewing c o n d i t i o n s i n a French brewery. The same experimental beers were then analyzed f o r 12 i n d i v i d u a l as w e l l as t o t a l carbon disulfide-extractable v o l a t i l e s , and four metal ions (K, Mg, Na, Ca). P r i n c i p a l component a n a l y s i s of each of the data sets (sensory and a n a l y t i c a l ) y i e l d e d c l a s s i f i c a t i o n s of the beers


100

FLAVOR

QUALITY:

OBJECTIVE

MEASUREMENT

i n each instance which were separated i n t o three d i s t i n c t groupings (assigned as good, average, or poor). While the groupings obtained f o r the sensory data e v a l u a t i o n were used as the b a s i s f o r q u a l i t y assignments, only two samples were m i s c l a s s i f i e d (changing from average to poor) when the a n a l y t i c a l data alone were used. Stepwise d i s c r i m i n a n t a n a l y s i s was then employed


Table VI.

C l a s s i f i c a t i o n of Beers i n t o Q u a l i t y Groupings (Good, Average, Poor) with Stepwise D i s c r i m i n a n t A n a l y s i s o f Physicochemical Data.

T o t a l Number of V a r i a b l e s

Variables Included

% of Beers Within Classes

13

11 V o l a t i l e s 2 Mineral Salts

94.2 (32/34)

11

9 Volatiles 2 Mineral Salts

91.2 (31/34)

7

5 Volatiles 2 Mineral Salts

82.4 (28/34)

From M o l l et a l .

(43).

to reduce the number of v a r i a b l e s r e q u i r e d to e f f e c t c l a s s i f i c a t i o n i n t o the q u a l i t y groupings (Table V I ) , and even when the data from only 5 v o l a t i l e s and 2 minerals were used, 82.4 percent of the beers were c o r r e c t l y c l a s s i f i e d i n t o the groups determined by sensory c h a r a c t e r i s t i c s . This degree of success f o r these samples i s s i m i l a r to that achieved by the same workers f o r 58 French and f o r e i g n beers using 8 physicochemical v a r i a b l e s s e l e c t e d from 38 i n i t i a l v a r i a b l e s , and c l a s s i f i c a t i o n i n t o good or passable c a t e g o r i e s . In t h i s study 80.5% of the samples were c o r r e c t l y c l a s s i f i e d by using data f o r 3 amino a c i d s , 3 v o l a t i l e s , 1 m i n e r a l , and the c o n c e n t r a t i o n of b i t t e r substances i n beer. An extension o f t h i s approach has been discussed by Dravnieks (15) where odor c h a r a c t e r i s t i c s of i n d i v i d u a l GC peaks from beers analyzed by an entrainment technique were q u a n t i f i e d and c o r r e l a t e d with some GC peak areas f o r c e r t a i n aroma types. While the report was l i m i t e d to d e s c r i p t i o n s of a few c o r r e l a t i o n s , the approach should prove u s e f u l i n the f u t u r e . In summary, evidence has been accumulated to show that beers can be d i f f e r e n t i a t e d and c l a s s i f i e d with the a i d of appropriate s t a t i s t i c a l a n a l y s i s of both physicochemical and sensory data.


7.

Lindsay


101

Initiation of routine analytical monitoring of flavor quality appears feasible with current gas chromatography and computer methodology, but with experience and refinements of procedures greater applications should follow soon. Literature Cited 1.


2. 3. 4. 5.

6.

7. 8. 9.

10.

11. 12. 13. 14.

15.

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Trachman, H. and Saletan, L. T. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1969), 19-28. Bavisotto, V. S., Roch, L. Α., and Heinisch, B. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1961), 16-20. Meilgaard, M. Elizondo, Α., and Mackinney, A. Wallerstein Laboratories Communications, (1971), 34 (114), 95-113. Mecredy, J . Μ., Sonnemann, J . C . , and Lehman, S. J . Food Technology, (1974), 28 (11), 36-41. Sidel, J . L., Stone, Η., Woolsey, Α., and Mecredy, J . M. Journal of Food Science, (1972), 37, 335. Einstein, M. A. Journal of Food Science, (1976), 41, 383-385. Kneen, E. (chr. ed. brd.). "Methods of Analysis of the American Society of Brewing Chemists," 7th ed., 1-200, American Society of Brewing Chemists, St. Paul, (1976). Hudson, J . R. Journal of the Institute of Brewing, (1960), 66, 1-102. Bishop, L. R. In: "Modern Brewing Technology" (Findlay, W. P. Κ., ed.), 292-323, Macmillan Press, London, (1971). Hough, J . S., Briggs, D. Ε . , and Stevens, R. "Malting and Brewing Science," 599-648, Chapman and Hall, London, (1971). Ashurst, P. R. In: "Modern Brewing Technology" (Findlay, W. P. K., ed.), 31-59, Macmillan Press, London, (1971). Doty, D. M. In: "Objective Methods for Food Evaluations," 3, National Academy of Sciences, Washington, (1976). "Correlation of Subjective-Objective Methods in the Study of Odors and Taste," ASTM STP 440, 1-107, American Society for Testing and Materials, Philadelphia, (1968). Powers, J . J . and Moskowitz, H. R. "Correlating Sensory Objective Measurements--New Methods for Answering Old Problems, ASTM STP 594, 1-134, American Society for Testing and Materials, Philadelphia, (1976). Powers, J . J . Food Technology, (1968), 22 (4), 383-388. Powers, J . J . and Keith, E. S. Journal of Food Science, (1968), 33, 207-213. Young, L. L., Bargmann, R. Ε . , and Powers, J . J . Journal of Food Science, (1970), 35, 219-223. Milutinovic, L., Bargmann, R. Ε . , Chang, Κ. Y . , Chastain, Μ., and Powers, J . J . Journal of Food Science, (1970), 35, 224-227. Dravnieks, Α., Reilich, H. G., Whitfield, J., and Watson, C. A. Journal of Food Science, (1973), 38, 34-39. Dravnieks, A. and Watson, C. A. Journal of Food Science, (1973), 38, 1024-1027. Dixon, W. J . (ed.). "BMD: Biomedical Computer Programs," 411-452, University of California Press, Los Angeles, (1975). Hoff, J . T . , Helbert, J . R., and Chicoye, Ε. MBAA Technical Quarterly, (1975), 12 (4), 209-213.

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Helbert, J . R. and Hoff, J . T. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1974), 43-46. Reiner, L. and Piendl, A. Brauwissenschaft, (1974), 27, 33-39. Brown, D. G. W., Clapperton, J . F . , and Dalgliesh, C. E. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1974), 1-4. Moll, Μ., Flayeux, R., That, V . , and Noel, J . P. Bios, (1974), 9, 328-333.


43.



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