ISOAMYL ACETATE--A KEY FERMENTATION VOLATILE OF WINES OF VITIS VINIFERA CV PINOTAGE

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1 ISOAMYL ACETATE--A KEY FERMENTATION VOLATILE OF WINES OF VITIS VINIFERA CV PINOTAGE C. J. van Wyk, O. P. H. Augustyn, P. de Wet, and W. A. Jubert Department f Oenlgy, University f Stellenbsch, Stellenbsch 7600, Suth Africa. We gratefully acknwledge the generus financial supprt f The Cape Wine and Spirit Institute. We als thank F. J. Malan, The C-perative Winegrwers Assciatin f Suth Africa (K. W.V.), and the cmmittees f the Bberg, Stellenbsch and Cape Wine Shws fr prviding mst f the wine samples essential t this investigatin. Manuscript submitted September 21, Revised manuscript received May 17, Accepted fr publicatin May 25, Yung red table wines f the cultivar Pintage (Vitis vinifera: Pint nir x Cinsaut) have a distinctive fermentatin buquet. This buquet is nt present in either the Pintage grapes r must but is knwn t be frmed during fermentatin. Isamyl acetate, when present in relatively large cncentratins, was shwn t be the "impact" cmpund respnsible fr this typical buquet. Wines frm ther cultivars t which isamyl acetate had been added were classified as being typically Pintage in the curse f a red varietal wine evaluatin. Examinatin f the results frm tw ABSTRACT f the 1975 Wine Shws indicated that the presence f this buquet is evidently cnsidered t be a psitive quality-enhancing factr. During aging this buquet gradually decreased in intensity and finally disappeared. This change was accmpanied by a cncurrent decrease in isamyl acetate cncentratin. A similar reductin in buquet intensity and isamyl acetate cncentratin was bserved when the wine was expsed t an excess f xygen, as well as elevated temperatures. Since the applicatin f sphisticated gas chrmatgraphy-mass spectrmetry techniques t the study f wine vlatiles, hundreds f arma and buquet cmpnents frm grapes and wine have been identified and in sme cases quantitated (1,6,7,20,21,22,23, 24,25,26,35). Substantial prgress has been made in the islatin and characteriatin f impact cmpunds essential t a specific grape r wine arma. The imprtance f mn- and sesquiterpenes in the arma f muscat grapes and wine has becme generally appreciated (3,28,34,36). Sme f these cmpunds are als present in the grapes and wine f ther varieties such as Riesling (20,21,22,25,29,30), Mfiller-Thurgau (8,25), Traminer (20,25), Rul~inder and Scheurebe (20,25) and Optima and Rieslaner (25). In these grapes and wines, whse armas are cnsidered by many experts t be nuances f the typical muscat arma, the specific varietal character seems t be crrelated t variatins in the cncentratins f terpenic alchls and their furanic and pyranic derivatives present (25). Pwer and Chesnut (17) fund that methyl anthranilate is an essential cmpnent f the arma f Cncrd grapes. Hlley et al. (9), hwever, pinted ut that methyl anthranilate alne was nt the nly cntributr t the typical Cncrd varietal arma. Methyl anthranilate has als been implicated as a majr cntributr t the "fxiness" typical f wines made frm certain native American grape varieties (19,37). Recent wrk, hwever, indicates that there is n crrelatin between the methyl anthranilate cntent and the "fxiness" f a wine (11). 167 Baynve et al. (1) identified 2-methxy-3- isbutylpyraine in juice frm Cabernet Sauvignn grapes. This is an extremely ptent arma cmpund (2,10) and as such it must play an essential rle in the "green" nuance that is typical f Cabernet Sauvignn arma (1). Yung red table wines f the Suth African variety Pintage (Vitis vinifera: Pint nir x Cinsaut) are renwned fr their characteristic fruity buquet. This buquet, hwever, des nt appear as such in either the must r the grape. This wuld seem t indicate that the typical character is frmed during fermentatin. This strng fruity buquet is nt equally prminent in all wines f this cultivar and althugh being cnsidered as typical f Pintage, it ccasinally appears in wines f the cultivars Cinsaut and Tinta Barcca. The intensity f this buquet in the latter cultivars is, hwever, appreciably belw the high levels generally attained in Pintage. The lcal ppularity f red Pintage wine prmpted the investigatin f the identity f the cmpund(s) respnsible fr the typical buquet and the cntributin f these cmpund(s) t the character and quality f such wines. MATERIALS AND METHODS All wines used in this investigatin were made in tw f the areas delimited fr wines f rigin in the Republic f Suth Africa, namely Stellenbsch and Bberg. Mst f the samples were frm the 1974 and 1975 vintages, but fr certain aspects f the wrk lder

2 168 m ISOAMYL ACETATE and yunger wines frm the same areas were used. Vlatiles were cncentrated as fllws. The wine (100 ml) was extracted with pure diethyl ether (33) (50, 20, 20 and 10 ml). After remving the acids by extractin with 5% Na2CO3 (20, 10 and 10 ml) and drying ver anhydrus MgSO4, the extract was cncentrated by distilling ff the ether thrugh a Vigreux-clumn in a water bath at 40 C. Mre reliable results were btained by cncentrating the ether extract immediately befre injectin. All gas chrmatgraphic wrk was dne n Perkin Elmer 900 instruments equipped with dual flame iniatin detectrs using nitrgen (40 ml/min) as carrier gas. The fllwing 10' x ¼" stainless steel clumns were used: 1. FFAP, 10% n Chrmsrb W AW DMCS, mesh. 2. Diglycerl, 10% n Gas-Chrm R, mesh. 3. OV-210, 10% n Chrmsrb W AW DMCS, mesh. The respective prgrams used n each f these clumns are as fllws: 1. Injectr temperature: 240 C, Manifld temperature: C. Oven temperature: 25 C fr 6 minutes then 50 C fr 2 minutes, fllwed by prgramming at 2 C per minute. 2. Injectr temperature: 180 C, Manifld temperature: 210 C. Oven temperature: isthermal at either 65 C r 80 C. 3. Injectr and manifld temperatures as fr 1. Oven temperature: 140 C fr 5 minutes fllwed by prgramming at 2 C per minute. Fr quantitative wrk, gas chrmatgraphically purified heptyl acetate in alchl was added t the wine as internal standard at a cncentratin f 15 mg/1 befre extractin. Quantificatin f peak areas was dne by triangulatin. Samples purified preparatively were cllected in glass capillary tubes cled by means f ice. The capillaries were sealed in a flame and stred at-5 C in the dark until needed. Infrared spectra were recrded n a Beckman IR-18A instrument fllwing the methd f van Wyk et al. (31). Sensry analysis f all wines was cnducted in an air cnditined rm at 20 C. The rm is equipped with cubicles which separate the seated tasters frm each ther as well as frm the serving area. Wines were presented ne at a time, in randm rder, thrugh a small pening with sliding dr in the wall facing the taster. Judging f shw wines was cnducted in an exhibitin hall accrding t the system suggested by Vedel and adapted by van Zyl (32). The wines were judged ne at a time and in a different rder by each judge. The scres reprted in this paper were recalculated frm the riginal scre cards by applying a simple mdificatin in the allcatin f pints, thus eliminating the ttal sum f squares as prescribed by Vedel. RESULTS AND DISCUSSION Islatin and identificatin f the cmpund respnsible fr the typical Pintage fermentatin buquet: Experience gained by sniffing wine vlatiles at the gas chrmatgraph exhaust led the authrs t believe that isamyl acetate (3-methyl-n-butyl acetate) may play an imprtant part in the typical Pintage fermentatin buquet. Using this idea as a basis the fllwingwrk was initiated. The retentin time f pure isamyl acetate was determined n the FFAP and diglycerl clumns. Pintage wines with the typical fermentatin buquet f lw and high intensity as well as Pintage wines lacking this buquet were extracted and examined n the FFAP clumn. Althugh there were minr variatins in the peak sies f the main esters and alchls nrmally fund in such wine extracts, the predminant and mst cnsistent variatin appeared in the sie f the peak crrespnding in retentin time t isamyl acetate. Withut exceptin each sample with a relatively high intensity f the typical Pintage fermentatin buquet shwed a relatively larger peak in this psitin than the samples withut the typical buquet. An extract f Pintage wine with the typical fermentatin buquet was fractinated n the FFAP clumn and the relevant peak islated. The main cnstituents in this peak were determined by sapnificatin with 3M NaOH. The resultant alchls were extracted with diethyl ether and separated n the diglycerl clumn. This manipulatin shwed yields f apprximately 90% isamyl alchl and apprximately 10% active amyl alchl. The relevant ester was thus shwn t be mainly isamyl acetate. The infrared spectra f the islated material and an authentic isamyl acetate sample crrespnded in all pertinent characteristics. The cncentratin f active amyl acetate is generally lw cmpared t that f isamyl acetate as was illustrated in the sample analyed abve. The threshld cncentratin f active amyl acetate, in a dedried wine medium, has been shwn t be fur times higher than that f isamyl acetate (5). It therefre appears reasnable t cnclude that the verall cntributin f the active amyl acetate t the wine buquet will be small cmpared t that f the isamyl acetate. This assumptin is supprted by arma values (18) f and 2.34 fr the is- and active ismers respectively, calculated frm a wine with a cmbined ismer cncentratin f 15 mg/1. Althugh arma values shuld be used with care, a difference f this rder f magnitude may be taken as an indicatin f arma effectiveness (18). In the ensuing discussins the influence f the active amyl acetate will therefre be ignred and the relevant peak referred t as isamyl acetate. Relatinship between isamyl acetate cntent and typical Pintage fermentatin buquet: In rder t determine a pssible relatinship between isamyl ace-

3 ISOAMYL ACETATE- 169 tate cntent and the typical Pintage fermentatin buquet, samples f all red table wines in the Pintage classes were cllected frm the 1975 Stellenbsch and Bberg Wine Shws. A panel f five judges, particularly experienced in detecting and evaluating this buquet, was requested t judge the intensity f the typical Pintage buquet f each wine. The intensity rating was as fllws: 1) absent (0 pints); 2) weak (1 pint); 3) mderate (2 pints); 4) strng (3 pints) and 5) very strng (4 pints). The isamyl acetate cntent was determined fr a few wines frm classes 1, 3, 4 and 5. The results are presented in Fig. 1. These results clearly shw the increased typical Pintage fermentatin buquet with increasing isamyl acetate cncentratin, a relatinship which is highly significant (P 0.01). The average isamyl acetate cncentratins fr the analyed samples in the abve mentined classes were 3.4, 7.6, 10.0 and 14.3 mg/1 respectively. ~3 n- 7D2 a. n~ uj 1 J "..". r = 0,88134 : ". " y : %07048x- 0,02?792,; 2b sb 20 ISOAMYL ACEIATE CONCENTRATION (mg/i) Fig. 1. The relatinship between bserved Pintage fermentatin buquet intensity and isamyl acetate cncentratin f shw wines. The next step was t examine the effect f adding isamyl acetate t a nn-pintage wine f relatively neutral buquet. Gaschrmatgraphically purified isamyl acetate was added t three different nn- Pintage wines in tw different cncentratins per wine. T avid unnecessary influencing f the panel thrugh cntinued expsure t the dr f the added isamyl acetate, as well as the prnunced fermentatin buquet f Pintage wines, the treated samples were included in a general varietal wine judging. The ther wines presented included Pintage wines withut the typical fermentatin buquet, wines f Cabernet Sauvignn, Shira, Cinsaut, Tinta Barcca and a blended wine. Twenty-fur experienced judges received the samples ne at a time in randm rder. Each wine was judged nce nly. Each taster received a chart resembling Table 1 but withut the secnd, third and last clumns and with the wines served being represented by cde numbers in clumn ne. The taster was asked t examine the sample presented and t name the variety. Wines which were nt regarded as typical f ne f the five named varieties were entered in the clumn marked ~ther". This mdus perandi was als selected t cnceal the fact that the presence r absence f the typical Pintage fermentatin buquet was the primary interest f the exercise. Every judge was thus able t determine the varietal relatinship f each sample in an unbiased way. The results are presented in Table 1. The percentage crrect identificatins f the tw typical Pintage samples is rather lw when cmpared with the typical Cabernet Sauvignn and Shira wines. This seemed t have been caused by the fact that the armas and/r buquets f the Pintage wines available were, althugh typical, nly f mderate intensity. The atypical Cinsaut was ne f the rather rare wines referred t in the intrductin. It had a decided Pintage fermentatin buquet and analysis shwed it t cntain 12.5 mg/1 isamyl acetate. The mst striking result in Table 1, hwever, is the prnunced increase in the percentage identificatin as Pintage in all cases where isamyl acetate had been added t nn-pintage wines. In view f these results, and in particular the magnitude f the differences in percentage identificatin as Pintage befre and after isamyl acetate additin, it can be cncluded that, within the limits f this experiment, the additin f isamyl acetate t nn- Pintage wines caused a radical change in the judges' appreciatin f these wines with respect t Pintage varietal character. The experience f the authrs with similar wines leaves little dubt that this assciatin, by the judges, f isamyl acetate with Pintage varietal character can primarily be attributed t its cntributin t Pintage fermentatin buquet rather than Pintage arma. In rder t cnfirm these results a further experiment using Pintage wines frm the 1978 vintage was planned. Fifteen Pintage wines, all f different rigin, were selected fr use in the experiment. In a preliminary screening by fur experienced judges their typical fermentatin buquets were rated frm absent t mderately strng. T these wines gas chrmatgraphically purified isamyl acetate was added in three different cncentratins vi. 8, 16 and 24 mg/1. These samples, which tgether with the fifteen untreated wines amunted t 60 in number, were then subjected t rganleptic evaluatin by the same 24-member panel f judges as befre. All samples were presented twice and in randm rder. The judges were requested t determine whether the typical fermentatin buquet was present and als assess the buquet intensity n the same basis as mentined earlier. Twenty samples were evaluated at each sessin. The untreated wines were analyed fr isamyl acetate as befre. The results are presented in Fig. 2. A highly significant crrelatin is shwn t exist between the amunt f isamyl acetate in the sample and the intensity f the typical Pintage fermentatin buquet. Cnsequently there appears t be n reasn t dubt the view that isamyl

4 ISOAMYL ACETATE Variety presented Table 1. The percentage f called identificatins in rganleptic tests f red varietal wines. Isamyl acetate added (mg/i) Trueness t Variety called % variety a Pintage Cabernet Shira Sauvignn Cabernet 1 0 Typical Cabernet 2 0 Typical Cabernet 3 0 Typical Cabernet 4 0 Atypical Shira 1 0 Typical Shira 2 0 Spiled Pintage 1 0 Atypical c Pintage 2 0 Atypical c Pintage 3 0 Typical c Pintage 4 0 Typical c Cinsaut 1 0 Typical T. Barcca 1 0 Typical T. Barcca 2 0 Typical T. Barcca 3 0 Atypical Cinsaut 2 0 Atypical Cinsaut Cinsaut T. Barcca 4 0 Atypical T. Barcca 4 10 ~ T. Barcca Red wine b 0 ~ Red wine Red wine adetermined by a different experienced panel f five members; als mentined in the text. ba mixture f T. Barcca, Cinsaut and thers. ctypical r atypical with respect t Pintage fermentatin buquet. dvalues with asterisk calculated, thers determined gas chrmatgraphically. Cinsaut Tinta Barcca Other Isamyl acetate cncentratin (mg/i) d m { " " * )-. uj 3 0 ~D _ w 5: uj u_ 2 w _ 14_ 1 p-,, * r : 0,9/./. y = 0,305x - O, ' ' ISOAMYL ACETATE CONCENTRATION (mg/l) Fig. 2. The relatinship between bserved Pintage fermentatin buquet intensity and isamyl acetate cncentratin f Pintage wines with and withut added isamyl acetate. acetate is indeed the cmpund mainly respnsible fr the typical fermentatin buquet which is frequently present in Pintage wines. An intriguing phenmenn amng the 1978 Pintage wines was the lw incidence f the typical Pintage fermentatin buquet. This cnditin prevailed even in wines with an isamyl acetate cncentratin that in nrmal years wuld have caused a buquet intensity rating f mderate t very strng. It wuld therefre appear as if the effect f the isamyl acetate in these wines was, t sme extent, masked by as yet unknwn factrs. This phenmenn can, hwever, pssibly be related t the vintage as the 1978 seasn was unusual due t lng spells f cl weather during the ripening perid. This phenmenn is under investigatin at present. Accrding t Webb et al. (35), the buquet f wine in general is nt due t an ~'impact" flavr cmpund but t a cmplex mixture f cmpunds. This generaliatin excludes "impact" flavr cmpunds present in the grape which are carried thrugh fermentatin unchanged. Schreier et al. (21) in their wrk n Riesling, Rul~inder, Traminer and Scheurebe wines supprted this view. They als pinted ut the imprtance f the terpenic alchls as well as their furanic and pyranic derivatives in the wine buquets examined by them. In their wrk n grape vlatiles Schreier et al. (25) fund amng the 200 identified cmpnents nly a few esters present in very small cncentratins. They suppsed that esters perhaps may nt have been genuine grape cnstituents and that thse fund in grape juice were frmed after destructin f the cell structure. This suppsitin wuld be in accrdance with the fact that Pintage grapes d nt have the arma typical f a Pintage wine. Here we thus have the unique instance f a varietal wine that is ften characteried by a cmpnent frmed during fermentatin.

5 ISOAMYL ACETATE m 171 The typical buquet as a factr in general quality: The intensity f the typical Pintage buquet may vary greatly frm wine t wine. Smetimes it is intense t the pint f being repulsive. Cncentratins f 25 mg/1 isamyl acetate have been determined and the ccurrence f even higher cncentratins is quite pssible. Several different terms are used by Suth African judges t describe this buquet, e.g. flwery, estery, banana-like (usually at lwer isamyl acetate cncentratins) and acetne-like. Althugh this buquet is generally recgnied as a characteristic f certain Pintage wines, it als, as already mentined, ccasinally ccurs in wines f ther cultivars. T illustrate this pint all the red varietal table wines entered in the Pintage, Cinsaut and Tinta Barcca classes at the 1975 Stellenbsch and Bberg Wine Shws were rganleptically examined by the befre mentined panel f tasters fr the presence r absence f a typical Pintage fermentatin buquet. The results are given in Table 2. It shuld be mentined that, althugh a few Cinsaut and Tinta Barcca wines shwed the particular buquet, the intensities were generally very lw. Only in ne instance, in a Tinta Barcca wine with a cncentratin f 14.4 mg/1, did the isamyl acetate cncentratin exceed 10 mg/1. Of the 13 nn-pintage wines exhibiting a typical Pintage buquet (Table 2), eight were analyed fr isamyl acetate. The average isamyl acetate cncentratin f these wines, barring that f the mentined Tinta Barcca, was 8.2 mg/1. The higher incidence f the typical buquet in wines frm the Stellenbsch district may be indicative f reginal effects. These reginal effects are presently being investigated. Sme cnsumers, as well as sme experienced judges, d nt accept this typical buquet as a desirable characteristic in red table wines and discriminate against it. It wuld, hwever, appear as if a large prprtin f the Suth African shw judges cnsider this typical buquet t be a psitive quality-enhancing characteristic. Analysis f the 1975 Stellenbsch and Bberg Wine Shw results supprt this statement. In Table 3 medals awarded and average marks gained are cmpared with average intensity f the typical and atypical buquet f the different entries. Frm Table 3 it is clear that the average marks awarded decreased in accrdance with decreasing isamyl acetate cncentratins and decreasing intensities f the typical buquet. Althugh nly 52% f the wines entered had the typical Pintage buquet, 76% f all medals awarded in the Pintage classes were wn by this grup. Only 24% f the entries had a strng t very strng typical Pintage buquet; nevertheless, 44% f all medals, including all the gld and ne third f the silver medals, were awarded t this grup. These results, which supprt the view that isamyl acetate is a quality-enhancing factr in Pintage wine buquet, are in cntrast with thse btained by Siht et al. (27) shwing the same ester t be a negative quality factr in beer buquet. Influence f xidatin and aging n the retentin f the typical Pintage fermentatin buquet: It is an accepted fact that the typical Pintage fermentatin buquet decreases with aging and unless the wine is stred at very lw temperatures this buquet usually disappears cmpletely after tw r mre years. Wines Table 2. Incidence f typical Pintage fermentatin buquet in red varietal table wines at tw different 1975 wine shws. Cultivar Wine Number Typical Pintage buquet district f entries f rigin Present Absent Number P erce nt age Number P erce nt age Pintage Stellenbsch Bberg Cinsaut Stellenbsch Bberg Tinta Stellenbsch Barcca Bberga.... aaii wines were nt available, therefre nt examined Pintage fermentatin buquet intensity Table 3. Divisin f shw hnrs between Pintage wines with r withut the typical fermentatin buquet. Samples rated fr Medals awarded Mean scres Pintage fermen- max: 100 tatin buquet (y) Number % Gld Silver Brne Ttal (%) High b Lw c Absent The crrelatin between (x) and (y) is highly significant'(r = 0.709). anumber f samples analyed t cmpute the average cncentratins; 10, 6 and 6 respectively. brepresented by classes 4 and 5 (see text). crepresented by classes 2 and 3 (see text). Mean isamyl acetate cncentratin (mg/i) a (x)

6 172 m ISOAMYL ACETATE stred in wden cntainers als tend t lse the typical buquet faster than equivalent wines stred in steel tanks. T illustrate the lss f typical buquet with aging, and the cncmitant decrease in isamyl acetate cncentratin, bttled wines f three cnsecutive vintages, frm an estate renwned fr the cnsistent appearance f the typical buquet in its wine, were analyed fr isamyl acetate cntent early in The fllwing cncentratins f this ester were fund: 1974 vintage, 24.9 mg/1; 1973 vintage, 14.0 mg/1; and 1972 vintage 2.1 mg/1. Althugh these results d nt take the nrmal annual fluctuatin f the initial isamyl acetate cncentratin int accunt, they d, hwever, clearly illustrate the general pattern. The influence f xygen and elevated temperature n the typical Pintage buquet was investigated as fllws. A yung Pintage wine cntaining the typical fermentatin buquet and with an isamyl acetate Cncentratin f 15.6 mg/1, was divided in tw. One half was thrughly sparged with xygen and the ther with xygen-free nitrgen and then sealed hermetically in a number f 150-ml glass ampules. One half f each batch was placed in an ven at 50 C and the ther half kept at 17 C. After specific intervals tw cntainers f each treatment were pened, the wines examined rganleptically and analyed fr isamyl acetate. The results are given in Table 4. It is interesting t nte that after 14 days at 50 C bth the xygen and nitrgen treated samples had n rganleptically detectable Pintage fermentatin buquet left. The xygen treated wine, hwever, was cmpletely ruined visually as well as rganleptically, whereas the nitrgen treated sample was nly slightly turbid and had develped an unpleasant buquet. Bth samples, hwever, had an isamyl acetate cncentratin f 10.6 mg/1 which under nrmal circumstances and accrding t the data in Fig. 1 wuld be enugh t cause a typical Pintage fermentatin buquet. In bth the abve cases the typical buquet is evidently effectively masked by the newly frmed maldrus cmpunds. As expected, the nitrgen treated samples kept at 17 C hardly differed frm the riginal at the terminatin f the treatment. The equivalent xygenated samples had n Pintage fermentatin buquet left at the end f the 28-day perid. There was little difference between the latter wines kept fr 14 days and 28 days respectively and bth wines were in a surprisingly fair cnditin. The isamyl acetate cncentratin thus decreased with all treatments at a greater r lesser rate and faster with xygenatin than withut. It is therefre bvius that excess xygen is detrimental t the typical Pintage fermentatin buquet, the desired buquet sn being superseded by the dr f the xidatin prducts. The typical Pintage fermentatin buquet wuld therefre be retained lnger if such wines are nt aged in small cperage, are bttled relatively yung and stred under cl cnditins: On the ther hand, a slightly different style f Pintage wine withut the typical fermentatin buquet will be btained by aging such a wine in small cperage r even large cperage ver a relatively lng perid f time. Table 4. Influence f xygen and elevated temperature n the typical Pintage fermentatin buquet. Treatment Strage Strage Mean temp. time i-amyl ac. ( C) (days) (mg/i) Cntrl m Sparged with 0 2 m Sparged with Sparged with Sparged with Sparged with Sparged with Sparged with Sparged with N 2 17 Sparged with N 2 17 Sparged with N 2 50 Sparged with N Cmments after sensry evaluatin Pleasant fruity typically Pintage Pleasant fruity typically Pintage Slight xidatin buquet - Pintage buquet still present thugh less than cntrl Oxidied character - slight Pintage nte detectable Oxidied character- strngly resembles same wine after 14 days Strng xidied character- slight Pintage nte still detectable Biled character - des nt resemble wine anymre - irreparably lst Over xidied Brwn sherry-like Pleasant fruity typically Pintage - intensity slightly less than cntrl Pleasant fruity typically Pintage - intensity less than previus sample Cked arma- unpleasant - n Pintage buquet left Unpleasant aged character - xidied CONCLUSION It has been shwn that the typical Pintage fermentatin buquet is caused by an increased isamyl acetate cncentratin. The rle, if any, f the ther esters in the verall typical buquet is at present being investigated. The prblem arises as t why the isamyl acetate cncentratins in sme wines are cnsiderably higher than in thers. The mechanism f ester frmatin has been thrughly investigated by NrdstrSm (12, 13,14,15,16). He als fund that esters are frmed within the yeast cell and that the genetics f the specific yeast strain might therefre play an imprtant rle in ester frmatin (12). If, hwever, the yeast strain alne was respnsible fr the frmatin f the typical isamyl acetate buquet, ne wuld expect the same result frm ther varieties fermented with the same yeast strain. Mre light is shed n this tpic by Daudt et al. (4). These authrs fund that the yeast strain, fermentatin temperature and the grape variety (Clmbard and Thmpsn Seedless) influenced ester frmatin during fermentatin. Our wrk n the Pintage fermentatin buquet supprts the latter finding and it culd be argued that this phenmenn is a genetic characteristic f the specific variety. The great variatin in isamyl acetate cncentratin in yung Pintage wines, hwever, indicates that impr-

7 ISOAMYL ACETATE m 173 tant thugh they may be, the yeast strain and the specific grape variety are nt the nly factrs respnsible fr the phenmenn bserved. Additinal factrs, yet t be determined, must therefre play an imprtant, if nt essential rle in the prcess as a whle. The fllwing bservatins may pint the way t the eventual identificatin f these unknwn factrs. There are definite indicatins that Pintage vines planted n certain sil series as a rule always yield wines with the typical buquet whereas vines frm the same stck planted n a different sil series d nt usually exhibit the typical buquet. Anther bservatin is that the maximum isamyl acetate cncentratin f a wine frm a specific vineyard, made by the same methds, may vary significantly frm ne vintage t anther. Research aimed at reslving the abvementined prblems cntinues in ur labratries. LITERATURE CITED 1. Baynve, C., R. Crdnnier, and P. Dubis. Etude d'une fractin caracteristique de I' ar6me du raisin de la variet6 Cabernet- Sauvignn" mise en evidence de la 2-m~thxy-3-isbutylpyraine. C. R. Acad. Sci. Paris, Serie D. 281:75-8 (1975). 2. Buttery, R.G., R. M. Seifert, D. G. Guadagni, and L. C. Ling. Characteriatin f sme vlatile cnstituents f bell peppers. J. Agric. Fd Chem. 17: (1969). 3. Crdnnier, R. Recherches sur I' armatisatin et le parfum des vins dux naturels et des vins de liquer. Ann. Technl. Agr. 5: (1956). 4. Daudt, C. E., and C. S. Ough. Variatins in sme vlatile acetate esters frmed during grape juice fermentatin. Effects f fermentatin temperature, SO2, yeast strain, and grape variety. Am. J. Enl. Vitic. 24:130-5 (1973). 5. De Wet, P., O. P. H. Augustyn, and C. J. van Wyk. T be published. 6. Drawert, F., and A. Rapp. Uber Inhaltsstffe vn Msten und Weinen. VII. Gaschrmatgraphische Untersuchung der Armastffe des Weines and ihrer Bigenese. Vitis 5: (1966). 7. Drawert, F., P. Schreier, and W. Scherer. 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