Capture and Use of Volatile Flavor Constituents Emitted during Wine

Chapter 12

Capture and Use of Volatile Flavor Constituents Emitted during Wine Fermentation

Downloaded by EAST CAROLINA UNIV on January 3, 2018 | http://pubs.acs.org Publication Date: August 23, 1993 | doi: 10.1021/bk-1993-0536.ch012

C. J. Muller, V. L. Wahlstrom, and K. C. Fugelsang Department of Enology, Food Science, and Nutrition and Viticulture and Enology Research Center, California State University, Fresno, CA 93740-0089

Wine v o l a t i l e flavor constituents originally present i n the grape or produced during the fermentation process are often lost into the atmosphere during the v i n i f i c a t i o n process due to t h e i r inherent v o l a t i l i t y and to entrainment with evolved carbon dioxide. Many compounds thus l o s t have positive sensory attributes; others are often construed as detrimental to the aroma and flavor of the wine. Selective capture, separation, concentration and addition of these v o l a t i l e s to the wines from whence they came can improve t h e i r quality.

V o l a t i l e compounds comprise a c r u c i a l c o n s t i t u e n c y i n determining the i d e n t i t y and complexity o f wines. Many o f these v o l a t i l e s are present o r i g i n a l l y i n the grape where they a r e produced by the myriad of biochemical i n t e r a c t i o n s during development, growth and r i p e n i n g . A f t e r harvest, other v o l a t i l e s are generated by chemical and biochemical r e a c t i o n s a r i s i n g from the inherent damage p e r p e t r a t e d on the grapes by the h a r v e s t i n g process. T h i s i s p a r t i c u l a r l y t r u e i n the case o f machine h a r v e s t i n g i n which c l u s t e r s a r e beaten o f f t h e v i n e s and where c o n s i d e r a b l e j u i c i n g occurs. More o f t e n than not, there are delays from t h e time of harvest u n t i l a c t u a l processing p r i o r t o v i n i f i c a t i o n beginning. During t h i s time, f u r t h e r r e a c t i o n s occur. These r e a c t i o n s a r e a c c e l e r a t e d by t h e r e l a t i v e l y high ambient temperatures prevalent during h a r v e s t . Upon c r u s h i n g , c e l l d i s r u p t i o n allows enzymes and s u b s t r a t e s t o comingle f r e e l y .

0097-6156/93/0536-0219S06.00/0 © 1993 American Chemical Society

Gump and Pruett; Beer and Wine Production ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


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In this environment, many new compounds are generated, a great p o r t i o n of them v o l a t i l e . I t i s a t t h i s time t h a t s k i n l i p i d s , f o r instance, might o x i d i z e w i t h the subsequent formation of s h o r t - c h a i n a l c o h o l s and aldehydes. Surely, j u d i c i o u s use of enzyme i n h i b i t o r s and a n t i o x i d a n t s such as s u l f u r d i o x i d e attenuate many of these changes. Unless the grapes are of optimal q u a l i t y , the winemaker must r e s o r t t o high l e v e l s of s u l f u r d i o x i d e t o prevent u n d e s i r a b l e changes. However, the c u r r e n t i n d u s t r y t r e n d i s f o r l e s s and l e s s use of s u l f u r d i o x i d e a t crush. Furthermore, by not u s i n g s u l f u r d i o x i d e , microorganisms, mostly the n a t i v e yeasts commonly found on grapes, might p r o l i f e r a t e with the concomitant production of t h e i r own m e t a b o l i t e s formed during i n c i p i e n t fermentation. Thus, a very complex mixture of v o l a t i l e s and t h e i r precursors already exist i n the grapes prior to v i n i f i c a t i o n . Some of these v o l a t i l e s are i n t i m a t e l y a s s o c i a t e d with the c h a r a c t e r i s t i c v a r i e t a l aroma; others are a s s o c i a t e d with i n c i p i e n t p r o c e s s i n g changes, and f i n a l l y , others are a s s o c i a t e d with d e f i n i t e chemical and m i c r o b i o l o g i c a l s p o i l a g e . The extent t o which these predominate i s obviously p r i m a r i l y contingent upon the q u a l i t y of the grapes at harvest, but a l s o t o the r a p i d i t y and care with which the harvesting, transporting, r e c e i v i n g and crushing operations are c a r r i e d out and, above a l l , the ambient temperature. V i n i f i c a t i o n as p r a c t i c e d i n most commercial w i n e r i e s i s i n i t i a t e d by i n o c u l a t i n g the must with e i t h e r a known c u l t u r e of a c t i v e l y growing wine yeast, o f t e n a f r e s h l y r e c o n s t i t u t e d wine a c t i v e dry yeast (WADY), or by t r a n s f e r r i n g a c t i v e l y fermenting must from another tank. G e n e r a l l y , white wines are fermented a t about 12 deg C (55 deg F) whereas red wines are fermented a t about 24-27 deg C (75-80 deg F) . Obviously, both fermentation r a t e and thus e v o l u t i o n of v o l a t i l e s , i n c l u d i n g carbon d i o x i d e and ethanol are faster at the higher fermentation temperatures. Fermentation

Volatiles

The i d e n t i t y of the v o l a t i l e c o n s t i t u e n t s produced d u r i n g fermentation has been the s u b j e c t of much s c r u t i n y (1,2,3,4,5,6) . Researchers are continuously adding t o t h i s seemingly unending l i s t . I t i s not the i n t e n t of t h i s paper t o dwell on each of the many compounds p r e s e n t l y i d e n t i f i e d . Instead we intend t o focus on the capture and u t i l i z a t i o n of those which emanate from fermentation tank vents while c o n s i d e r i n g them as a group. The amount and nature of the v o l a t i l e s evolved d u r i n g fermentation depends not only on fermentation temperature and grapes used and, as i n d i c a t e d above, on chemical and biochemical changes o c c u r r i n g p r i o r t o fermentation, but a l s o on the type of yeast used (7). Yeast s t r a i n s are known t o d i f f e r markedly on t h e i r reducing a b i l i t y . Some


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are capable of reducing s u l f a t e t o hydrogen s u l f i d e (8,9). Yeast s t r a i n s a l s o d i f f e r i n t h e i r a b i l i t y t o produce f l a v o r c o n s t i t u e n t s under normal c o n d i t i o n s (10). Other concurrent fermentations; e.g.: m a l o - l a c t i c a r e d e f i n i t e l y another source of v o l a t i l e s emanating d u r i n g the fermentation process. Many winemakers purposely induce a m a l o - l a c t i c fermentation e a r l y , whereas others a l l o w the y e a s t fermentation t o e i t h e r proceed o r t o be complete before i n o c u l a t i n g with m a l o - l a c t i c b a c t e r i a (11) . Some o f the v o l a t i l e s emanating from such fermentations have d e f i n i t e p o s i t i v e sensory a t t r i b u t e s . E f f e c t o f Temperature In g e n e r a l , v o l a t i l e c o n s t i t u e n t production i n c r e a s e s with i n c r e a s i n g fermentation temperature. A l s o , so does the l o s s i n t o t h e atmosphere of those c o n s t i t u e n t s with the highest v o l a t i l i t i e s . These i n c l u d e some very d e l i c a t e aromas a s s o c i a t e d w i t h the f r u i t y and v a r i e t a l c h a r a c t e r i s t i c s o f t h e grape as w e l l as some o f the compounds a s s o c i a t e d w i t h t h e vinous c h a r a c t e r of the fermenting must. Thus, white wines are t r a d i t i o n a l l y fermented a t lower temperatures i n an e f f o r t t o r e t a i n w i t h i n the fermenting must as many of these v o l a t i l e s as p o s s i b l e . Red wines on the other hand, are fermented a t higher temperatures i n an e f f o r t t o e x t r a c t as much c o l o r (and o f t e n tannins) as r e q u i r e d f o r the type o f wine being made. Under these circumstances, i t i s customary t o thoroughly mix s o l i d s and l i q u i d ("must") by pumping from the bottom of the tank over the s o l i d s ("cap") which f l o a t on top of the fermenting l i q u i d . T h i s process i s c a l l e d "pumpover". I t i s done t o e x t r a c t c o l o r and, perhaps more importantly, t o prevent the cap from d r y i n g . A dry cap o f t e n l e a d i n g t o the p o t e n t i a l o x i d a t i o n of ethanol and other metabolites t o produce compounds such as a c e t i c a c i d which, i f present i n l a r g e c o n c e n t r a t i o n s , a r e f r a n k l y o b j e c t i o n a b l e . Surely, the process o f pumping over i t s e l f allows v o l a t i l e c o n s t i t u e n t s t o be l o s t i n t o the atmosphere with great f a c i l i t y . Yeast which are temperature s t r e s s e d o f t e n produce uncommon v o l a t i l e s , or higher amounts of u n d e s i r a b l e v o l a t i l e s such as f u s e l o i l s (12). Production o f f u s e l o i l s i s a l s o enhanced when the yeast a r e s t r e s s e d by l a c k of sugars, as occurs toward the end of fermentation. E f f e c t o f Skin Contact White wines are given very l i t t l e s k i n c o n t a c t by most winemakers. As i n d i c a t e d above, r e d wines on t h e other hand are given considerable skin contact during fermentation. Many winemakers p r e f e r t o separate the pomace w e l l before the completion of fermentation whereas


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others allow the fermentation t o reach completion p r i o r t o pressing. Grape skins contain a complex mixture of carbohydrates, tannins and l i p i d s with a s m a l l amount o f p r o t e i n . However, some o f the most a c t i v e grape enzymes are present i n the s k i n . These i n c l u d e s e v e r a l oxygenases, polyphenol oxidases and lipoxygenases (13), a l l of which are capable o f r a p i d l y breaking down complex s u b s t r a t e s t o produce v o l a t i l e c o n s t i t u e n t s . Thus, i t i s apparent t h a t many p o t e n t i a l l y b e n e f i c i a l compounds a r e being produced which a r e simply l o s t i n t o the atmosphere during the fermentation process. Were t h e r e ways t o capture and r e i n c o r p o r a t e these c o n s t i t u e n t s i n t o the wine i t i s conceivably p o s s i b l e t o i n c r e a s e t h e q u a l i t y of such wine. However, the process i s not as simple as i t seems inasmuch as c o n s t i t u e n t s having p o s i t i v e a t t r i b u t e s , a r e i n t i m a t e l y comingled with many c o n s t i t u e n t s d e t r i m e n t a l t o aroma and f l a v o r . Any e f f o r t t o enhance wine q u a l i t y by r e i n c o r p o r a t i n g v o l a t i l e s produced d u r i n g fermentation must a l s o be concerned with the s e p a r a t i o n o f u n d e s i r a b l e compounds o r c l a s s e s of compounds p r i o r t o i n c o r p o r a t i o n . Collection of V o l a t i l e s The technology f o r capture of emission c o n t r o l v o l a t i l e s has been implemented f o r a long time i n the petroleum and chemical i n d u s t r i e s . These i n d u s t r i e s have been the focus of much s c r u t i n y by the v a r i o u s government agencies e n t r u s t e d with e n f o r c i n g environmental q u a l i t y . However, only r e c e n t l y has the wine i n d u s t r y been s u b j e c t e d t o s i m i l a r s c r u t i n y , and then only i n C a l i f o r n i a where t h e C a l i f o r n i a A i r Resources Board, and l a t e l y regional A i r Quality Control D i s t r i c t s , have been investigating the extent t o which wineries might c o n t r i b u t e t o atmospheric p o l l u t i o n (14). I t i s i n t h i s regard t h a t we, a t C a l i f o r n i a S t a t e University Fresno have been i n v o l v e d with studying emission control from winery fermentation tanks (15,16,17). As a d i r e c t r e s u l t of these s t u d i e s , we have i n p l a c e emission c o n t r o l devices centered around c h a r c o a l a d s o r p t i o n t r a p s . Such devices have been used t o c o l l e c t and capture fermentation emission v o l a t i l e s f o r t h e i r i d e n t i f i c a t i o n and a l s o f o r s t u d i e s l e a d i n g t o wine q u a l i t y enhancement (18) . Equipment P i l o t p l a n t fermentation equipment used f o r these s t u d i e s at CSU-Fresno, c o n s i s t s of four 1412-gallon s t a i n l e s s s t e e l j a c k e t e d and i n s u l a t e d fermentors p r o v i d e d with s t a i n l e s s s t e e l capture hoods as d e s c r i b e d elsewhere (17) . The capture hood i s connected with 1-inch s t a i n l e s s s t e e l square t u b i n g t o a foamover v e s s e l . From here, t h e l i n e goes f i r s t t o a heat exchanger where t h e v o l a t i l e


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stream i s then cooled t o about 4 deg C t o remove as much moisture as p o s s i b l e , followed by a preheater. A rotary vane pump l o c a t e d downstream provides a s l i g h t reduced p r e s s u r e onto the fermentation tank t o remove v o l a t i l e s . The same pump, on i t s discharge s i d e , p r o v i d e s a s l i g h t pressure t o d i r e c t the stream onto p a r a l l e l - c o n n e c t e d s t a i n l e s s s t e e l v e s s e l s c o n t a i n i n g a c t i v a t e d c h a r c o a l (see Figure 1).


Desorption During normal operation, appropriate v a l v i n g allows one of the c h a r c o a l adsorption v e s s e l s t o be i n t h e a d s o r p t i o n mode while the other i s e i t h e r being regenerated o r i s idle. Upon s a t u r a t i o n of the c h a r c o a l with v o l a t i l e s , r e g e n e r a t i o n and concomitant removal o f t h e adsorbed v o l a t i l e s i s accomplished by d i r e c t i n g c l e a n , d r y steam i n counter-current f a s h i o n . The v o l a t i l e - l a d e n steam i s t h e r e a f t e r condensed and c o l l e c t e d i n a s t a i n l e s s s t e e l v e s s e l (4 deg C) . A dry i c e s t a i n l e s s s t e e l t r a p l o c a t e d downstream c o l l e c t s any uncondensed l i g h t v o l a t i l e s . Concentration of V o l a t i l e s V o l a t i l e s captured as described above a r e then e x t r a c t e d 10 times with 50 mL a l i q u o t s of f l u o r o t r i c h l o r o m e t h a n e (Freon-11, A l d r i c h 24,499-1). The f r a c t i o n s a r e combined, d r i e d over anhydrous sodium s u l f a t e and t h e s o l v e n t evaporated i n a r o t a r y evaporator. The concentrated v o l a t i l e s thus obtained are kept under n i t r o g e n a t -40 deg C until utilization. We have not attempted a q u a n t i t a t i v e recovery o f a l l v o l a t i l e s emanating during fermentation. There i s v a s t v a r i a b i l i t y i n the amount of v o l a t i l e s produced i n each and every fermentation tank. Subtle d i f f e r e n c e s i n temperature, degree of mixing and other f a c t o r s p r o v i d e f o r d i s c r e p a n c i e s i n the fermentation r a t e and thus i n the v o l a t i l e s being produced and t h e i r time of emergence. However, i n our capture experiments we always attempted t o t r a p as much of t h e v o l a t i l e f r a c t i o n as possible. I t was apparent a t t h e time c o l l e c t i o n s were being made t h a t some very ephemeral c o n s t i t u e n t s were l o s t i n t o the atmosphere r e g a r d l e s s of a l l t h e p r e c a u t i o n s being taken t o t r a p and c o l l e c t them. Some of these c o n s t i t u e n t s had f l o r a l connotations t h a t undoubtedly would have made a very p o s i t i v e c o n t r i b u t i o n t o t h e aroma of t h e wine. Unfortunately, s i n c e they a r e so d i f f i c u l t t o capture t h e i r i d e n t i t y and p o s s i b l e c o n t r i b u t i o n i s not known a t present. I t i s important t o p o i n t out a t t h i s time t h a t the whole process of capture, adsorption, d e s o r p t i o n and c o n c e n t r a t i o n n a t u r a l l y s e l e c t s some c o n s t i t u e n t s a t the expense o f others. Therefore, the r e c o n s t i t u t e d v o l a t i l e f r a c t i o n only roughly resembles the a c t u a l c o n s t i t u e n c y of the v o l a t i l e s emanating from the fermentation tank vents




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d u r i n g t h e fermentation process. Furthermore, i t i s a w e l l known f a c t t h a t some c o n s t i t u e n t s might e x h i b i t p o s i t i v e a t t r i b u t e s when i n very d i l u t e s o l u t i o n whereas i n concentrated form they might be f r a n k l y d e t r i m e n t a l t o the o v e r a l l aroma and bouquet sensation. A l s o , i t must be recognized t h a t s y n e r g i s t i c e f f e c t s , both p o s i t i v e and negative, e x i s t among compounds i s o l a t e d in this fashion just like they exist i n other environments. Thus the a d d i t i o n of the v o l a t i l e f r a c t i o n as a whole o r i n p a r t t o the wine poses a d e f i n i t e challenge inasmuch as the r e s u l t s a r e not always predictable. Addition of V o l a t i l e s In our i n i t i a l work, the v o l a t i l e f r a c t i o n was c o l l e c t e d , e l u t e d from the c h a r c o a l , e x t r a c t e d from t h e aqueous phase w i t h Freon-11, and the solvent evaporated as d e s c r i b e d above. No attempt was made a t t h i s time t o separate t h e whole v o l a t i l e f r a c t i o n i n t o s u b f r a c t i o n s by e i t h e r b o i l i n g p o i n t or f u n c t i o n a l i t y . Instead, the v o l a t i l e s thus obtained were added back t o wines from which they came i n v a r i o u s r a t i o s and the r e s u l t i n g wines subjected to sensory e v a l u a t i o n by f i r s t , a t r a i n e d panel, and then a "consumer" panel. The purpose here was t o a s c e r t a i n i f such a d d i t i o n s indeed improved the q u a l i t y of the wines as expected. Both panels were requested t o evaluate both i n t e n s i t y o f aroma/bouquet and preference f o r each sample. Wine t o which no v o l a t i l e s had been added served as control. Results R e s u l t s a r e shown g r a p h i c a l l y i n Figures 2 and 3 f o r a white wine, and 4 and 5 f o r a r e d wine. Both wines were made from CSUF grapes and fermented d r y . Data obtained therewith showed t h a t i t i s indeed p o s s i b l e t o achieve a modest improvement i n the aroma/bouquet of both white and red wines (18). However, i t was a l s o apparent t h a t such improvement was contingent upon the r a t i o of a d d i t i o n of v o l a t i l e f r a c t i o n t o wine. In the case of white wine f o r i n s t a n c e , a d d i t i o n of v o l a t i l e s t o wine i n a 1:1 r a t i o , o r IX a d d i t i o n , r e s u l t e d i n wines with a l e s s e r score both i n terms o f i n t e n s i t y and of preference than wines i n which the a d d i t i o n was c a r r i e d out a t higher r a t i o s . In each case t h e f i r s t f i g u r e i n the r a t i o i n d i c a t e s the volume of fermenting must from which v o l a t i l e s were captured t o be added back; t h e second f i g u r e i n d i c a t e s the volume o f wine to which those v o l a t i l e s were added. No s i g n i f i c a n t increase (at p

Capture and Use of Volatile Flavor Constituents Emitted during Wine

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