Beer and Wine Production - ACS Publications - American Chemical

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

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