LWT 39 (26) 199 25 www.elsevier.com/locte/lwt Effect of ok rrel type on the voltile composition of wine: Storge time optimiztion Teres Grde Cerd n, Crmen Ancı n-azpilicuet Deprtment of Applied Chemistry, Universidd Púlic de Nvrr, Quimic Aplicd, Cmpus de Arrosdí s/n, E-316 Pmplon, Spin Received 12 Novemer 24; received in revised form 2 Jnury 25; ccepted 27 Jnury 25 Astrct When it comes to deciding out the length of time for geing wine in rrels it is necessry to tke into ccount severl fctors such s wine composition nd chrcteristics of rrels. Adpting wood to wine is not n esy mtter. Ageing durtion is highly vrile depending on wine s origin, type nd qulity. The im of this study is to investigte the ehviour of new rrels nd once-used rrels depending on the geing period of wine. From the results otined it cn e seen tht for geing wine during short period (6 9 months), there ws quite ig difference in the concentrtion of most of the ok wood compounds etween wine ged in new rrels nd wine ged in once-used rrels. However, due to the chemicl or iochemicl trnsformtions of certin compounds from ok wood in wine over time, their concentrtion in long-term geing (12 15 months) ws similr for oth wine ged in new rrels nd in once-used rrels. The compounds which ecme more exhusted from rrel use were, furnic ldehydes, phenolic lcohols, phenolic ldehydes, nd ok-lctones. r 25 Swiss Society of Food Science nd Technology. Pulished y Elsevier Ltd. All rights reserved. Keywords: Storge time; New nd once-used ok rrels; Voltile composition; Ethylphenols; Ok compounds; Red wines 1. Introduction Ok rrels hve een commonly used in the geing of wine nd spirits ecuse of their positive effects on the product. These include incresed colour stility, spontneous clrifiction, nd more complex rom. Ok composition nd the conditions in which wine mturtion tkes plce re of primry importnce on the impct of ok on wine qulity. Extrction of voltile compounds from ok rrels depends minly on the quntity of compounds tht re potentilly extrctle, on the contct time etween wine nd wood nd on the wine composition. This ltter fctor hs een the lest studied. In n erlier study Grde-Cerd n, Torre-Gon i, nd Ancı n-azpilicuet (24) found tht the lcoholic level of the wine fvours the extrction of voltile compounds from the ok rrels. Corresponding uthor. Tel.: +34 948 16899; fx: +34 948 16966. E-mil ddress: ncin@unvrr.es (C. Ancín-Azpilicuet). The fctors which ffect the pool of ok extrctives re species nd geogrphicl origin of the wood (Miller, Howell, Michelis, & Dickmnn, 1992; Ancı n, Grde, Torre, & Jime nez, 24), sesoning of the stves (Sefton, Frncis, Pocock, & Willims, 1993; Cdhı, Mun oz, Fern ndez de Simo n, & Grcı -Vllejo, 21), tosting of the rrel (Chtonnet, Boidron, & Pons, 1989; Hle, McCfferty, Lrmie, Newton, & Swn, 1999) nd rrel ge (Pe rez-prieto, Lo pez-roc, Mrtínez-Cutills, Prdo-Mı nguez, & Gómez-Plz, 22; Grde-Cerdán, Rodríguez-Mozz, & Ancı n-azpilicuet, 22). Ech rrel hs life history, sed on the pool of extrctle compounds it contined initilly, on the numer nd length of extrctions or fills for which it ws used nd on the wine composition ged in rrel. Contct time etween wine nd wood is very importnt nd needs continul surveillnce s some of the wine compounds increse with time while others undergo chemicl or iochemicl trnsformtions (Grde-Cerd n, Torre-Gon i, & Ancıń-Azpilicuet, 22; Pérez-Prieto, 23-6438/$3. r 25 Swiss Society of Food Science nd Technology. Pulished y Elsevier Ltd. All rights reserved. doi:1.116/j.lwt.25.1.9
2 ARTICLE IN PRESS T.G. Cerdán, C. Ancín-Azpilicuet / LWT 39 (26) 199 25 Lo pez-roc, Mrtínez-Cutills, Prdo-Mínguez, & Go mez-plz, 23). Idelly, no wine would remin in rrel for ny longer thn tht moment it hs reched its mximum qulity. It is elieved tht new rrels provide strong ok chrcter in the wine wheres rrels tht hve lredy een used once provide more discreet rom to the wine. However, ppers tht hve studied the exhustion of ok compounds in once used rrels nd tht show reltionship etween the rrel ge nd the geing period of wine re scnt. Accordingly, Rous nd Alderson (1983) studied the evolution of totl phenolics nd nonflvonoid phenolics during geing of white wines in new rrels, nd in second fill rrels nd third fill rrels. Towey nd Wterhouse (1996) studied the evolution of furnic compounds, cis nd trns-ok lctones nd phenolic lcohols in Chrdonny wines ged during 7 months in ok rrels during three successive vintges. The im of this work ws to study the extrction nd evolution of ok wood voltile compounds in wine ged during 15 months in oth new nd once-used rrels. In this wy, it ws hoped (1) to show the extent of exhustion of the rrels fter 15 months use; (2) to optimize the utiliztion of the rrels, new or once-used, depending on storge time. To do this, two lended wines were used, Cernet Suvignon Merlot (2 vintge) nd Grnch Merlot (21 vintge), with similr composition (12.5% nd 12.6% lcohol v/v, nd ph, 3.4 nd 3.3, respectively). Since there re usully some differences in wine from one hrvest to nother, the second wine ws chosen so tht it would hve the sme ph nd lcohol level s the first wine. These two fctors were kept in mind ecuse they re the two prmeters which hve n influence on the extrction of wood compounds. Cernet Suvignon Merlot wine ws ged in new Americn ok rrels during 15 months nd susequently Grnch Merlot wine ws then ged during 15 months. The rrels remined in the winery under the sme conditions of humidity nd temperture. 2. Mterils nd methods 2.1. Smples nd vinifiction The first step ws to ge wine lend of Cernet Suvignon (6%) nd Merlot (4%) in three new ok rrels during 15 months. Afterwrds, these sme rrels were used gin to ge wine lend of Grnch (3%) nd Merlot (7%) lso during 15 months. The elortion of the wines took plce in the cellr nd n identicl process ws used for ll vrieties. The grpes were destemmed nd crushed efore eing put into stinless steel tnks. Mcertion ws crried out during fermenttion with periodicl pumping over. The lcoholic fermenttion ws mde t 28 1C nd rought to Tle 1 Enologicl prmeters of Cernet Suvignon (6%) Merlot (4%) nd Grnch (3%) Merlot (7%) wines stored in new nd used-once rrels, respectively Cernet Suvignon Merlot Grnch Merlot Alcohol level 12.5 12.6 % (v/v) Totl cidity 6.3 6.5 g/l ph 3.4 3.3 Voltile cidity c.32.33 g/l Free SO 2 31.3 3. mg/l Totl SO 2 6.8 55 mg/l Sugr 1.9 1.9 g/l Dry extrct 29.7 3 g/l Mesured ccording to the methods descried y the Office Interntionl de l Vigne et du Vin (199). Expressed s trtric cid. c Expressed s cetic cid. dryness. The wines underwent mlolctic fermenttion efore eing put into the rrels. Generl prmeters for chrcterizing ech wine re shown in Tle 1. Here, it cn e seen tht oth wines showed similr ph nd lcoholic level. All rrels used were mde of Americn ok (Quercus l). The wood ws nturlly sesoned for 36 months nd during cooperge the wood ws sumitted to medium tosting. All the rrels were fricted t the Lfitte cooperge (Cognc, Frnce). All the rrels hd the sme conditions of humidity nd temperture in the cellr. Wine smples to e nlysed were tken from ech rrel fter 6, 9, 12, nd 15 months of geing. 2.2. Anlysis of voltile compounds of wines y gs chromtogrphy The compounds studied were: 2-furncroxldehyde (furfurl), 5-methyl-2-furncroxldehyde (5-methylfurfurl), 5-hydroxymethyl-2-furncroxldehyde (5- hydroxymethylfurfurl), 2-furnmethnol (furfuryl lcohol), 4-hydroxy-3-methoxyenzldehyde (vnillin), 3,5-dimethoxy-4-hydroxyenzldehyde (syringldehyde), 4-llyl-2-methoxyphenol (eugenol), 2-methoxyphenol (guicol), 4-methyl-2-methoxyphenol (4-methylguicol), cis--methyl-g-octlctone (cis-ok lctone), trns-methyl-g-octlctone (trns-ok lctone), 4-ethylphenol, nd 4-ethyl-2-methoxyphenol (4-ethylguicol). The extrction nd nlysis of these compounds were mde following the method descried in Grde-Cerd n et l. (22). To do so, mixture of n-pentnedichloromethne (3:2, v/v) ws used s extrcting solvents; oth solvents were from Pnrec (Montcd nd Reixc, Brcelon, Spin). The identifiction nd quntifiction of the voltile compounds ws crried out with GC-MS Finnign (Sn Jose, CA, USA). A DB- WAX cpillry column (3 m.25 mm i.d. nd
T.G. Cerdán, C. Ancín-Azpilicuet / LWT 39 (26) 199 25 21.25 mm film thickness) with sttionry phse of polyethylene glycol onded nd cross-linked (Croml, Brcelon, Spin) ws used. The volume of smple injected ws in ll cses 1 ml. The ioniztion ws producted y electronic impct t 7 ev. The internl stndrds used were 2-octnol (Aldrich, Gillinghm, Englnd) nd 3,4-dimethylphenol (Merck, Drmstdt, Germny). Stndrd solutions were prepred from Aldrich regents dissolved in synthetic wine (lcohol 13%, v/v), whose ph ws djusted to 3.2 with NOH 3 mol/l. The synthetic wine ws prepred y diluting 3 g of trtric cid (Sigm Chemicl Co., St Louis, MO, USA) nd 65 ml of ethnol (Merck) in deionized wter up to 5 ml. This resulting wine underwent the sme process of extrction s the smples. The results shown in figures re the rithmetic verge of six nlyses, since representtive smple ws tken from three rrels nd from ech smple two extrctions were mde of the voltile compounds to e nlysed. All the results of the figures re shown with their stndrd devition (Miller & Miller, 1988). The dt were nlysed sttisticlly using the vrince nlysis. Differences etween mens were compred using the LSD test t.5 proility level. 3. Results nd discussion The compounds which initilly showed the highest difference of concentrtion etween the first nd the second use of rrels were furnic ldehydes. The concentrtion of furfurl in the wine fter 6 months geing in the once-used rrels ws 98% lower thn in the wine ged in new rrels, while the concentrtion of 5-methylfurfurl diminished some 96% (Fig. 1() nd ()). Towey nd Wterhouse (1996) lso found tht the concentrtion of these sustnces diminished to n importnt extent, fter 7 months wine geing, when the sme rrels were used consecutively. However, for longer period of geing (12 15 months), it ws found tht the concentrtion of furfurl ws similr for oth the wine ged in new rrels nd tht ged in the onceused rrels (Fig. 1()). In the cse of 5-methylfurfurl the concentrtion ws somewht higher in the wine ged in new rrels (Fig. 1()). This is due to the fct tht the iologicl reduction of furfurl in order to form the corresponding lcohol is fster thn tht of 5-methylfurfurl (Spillmn, Pollnitz, Licopoulos, Prdon, & Sefton, 1998). Furfurl cn lso trnsform into 2- furnmethnethiol through micro-iologicl or chemicl mechnisms (Toming, Blnchrd, Drriet, & Duourdieu, 2). As regrds 5-hydroxymethylfurfurl, its concentrtion diminished with the use of the rrels somewht less thn the two ove-mentioned compounds. After 6 months, it showed 78% lower concentrtion in wine ged in once-used rrels thn in wine ged in new rrels (Fig. 1(c)). This compound ws extrcted during 9 months geing nd fterwrds, its concentrtion diminished until it prcticlly disppered from the 1 Furfurl 2 5-Methylfurfurl 75 5 25 () 12 9 (c) 6 3 5-Hydroxymethylfurfurl () (d) 15 1 5 1 75 5 25 Furfuryl lcohol New rrels Once-used rrels Fig. 1. Evolution of the concentrtion (mg/l) of furfurl, 5-methylfurfurl, 5-hydroxymethylfurfurl nd furfuryl lcohol for wines ged in new nd once-used ok rrels. Ech point is the men7stndrd devition of six replictes. For ech geing period, different letters indicte significnt differences etween the smples (Po:5).
22 ARTICLE IN PRESS T.G. Cerdán, C. Ancín-Azpilicuet / LWT 39 (26) 199 25 smples. Just s occurred with furfurl nd 5-methylfurfurl, for short geing periods importnt differences were found in the concentrtion of 5-hydroxymethylfurfurl etween wine ged in new rrels nd in onceused rrels. However, in long-term wine geing these differences were not found. Furfuryl lcohol does not come from wood ut rther it is formed through reduction of furfurl. This compound ws formed during the first 9 months of geing in oth smples (Fig. 1(d)), lthough to higher degree in wine ged in new rrels where the extrction of furfurl ws higher (Fig. 1()). Afterwrds, its concentrtion diminished in oth wines s it trnsformed into furfuryl ethyl ether (Spillmn et l., 1998; Vnderhegen et l., 24). The concentrtions of furnic compounds were elow tht of their threshold level (Tle 2). However, these compounds cn increse the rom of ok-lctones (Rezin, 1981). Phenolic ldehydes (Fig. 2() nd ()) lso showed importnt differences in their concentrtion etween wine ged in new rrels nd in once-used rrels, for short-term geing (6 months). After 6 months, the wine ged in the once-used rrels hd 65% less vnillin nd 67% less syringldehyde thn tht found in wine ged in new rrels. However, for long-term geing their concentrtions were similr in the wines ged in oth types of rrel s these compounds reduce to form the corresponding lcohols (Spillmn, Pollnitz, Licopoulos, Skouroumounis, & Sefton, 1997; Pollnitz, 2). Vnillin, the principl rom component of nturl vnill is generlly considered to e n importnt contriutor to the qulity of rrel-ged wines nd spirits (Morles, Benitez, & Troncoso, 24). This compound showed concentrtions higher thn its perception threshold (Tle 2) in oth wines fter 9 months geing, lthough its concentrtion ws higher in wine ged in new rrels (Fig. 2()). For long-term geing (12 15 months) the concentrtion of vnillin diminished nd the difference in concentrtion etween the two wines ws negligile. Syringldehyde, due to its high perception threshold (Tle 2), hrdly mkes ny contriution to wine rom, lthough it cn increse the rom of vnillin. The difference in concentrtions of phenolic lcohols, fter 6 months, etween the wine ged in new rrels nd in once-used rrels ws some 47% for eugenol, 73% for guicol nd 93% for 4-methylguicol (Fig. 2(c) (e)). Towey nd Wterhouse (1996) lso found tht guicol nd 4-methylguicol prcticlly disppered fter the first use of the rrels. Guicol nd 4-methylguicol form t high tosting tempertures nd since the rrels utilized in this study hd een sumitted to medium tosting, the concentrtions would consequently hve een quite low nd, perhps for tht reson, they would hve ecome exhusted to n importnt extent fter their first use. The fct tht Tle 2 Dt of perception thresholds (mg/l), in red wines, of voltile compounds studied Furnic compounds Furfurl 2 5-Methylfurfurl 45 5-Hydroxymethylfurfurl Furfuryl lcohol 45 Voltile phenols Vnillin Syringldehyde Eugenol Guicol 4-Methylguicol -Methyl-g-octlctone Cis isomer Trns isomer Ethylphenols 4-Ethylphenol 4-Ethylguicol Percepcion threshold 32 5 5 75 65 46 46 c 62 d 14 d Boidron, Chtonnet, nd Pons (1988). Wilkinson, Elsey, Prger, Tnk, nd Sefton (24). c Chtonnet, Boidron, nd Pons (199). d Chtonnet, Duourdieu, Boidron, nd Pons (1992). eugenol ws the phenolic lcohol tht lest diminished its concentrtion from use of the rrels, my e ecuse this compound is found in untosted ok s well s in young wine. Unlike tht which occurred with the furnic nd phenolic ldehydes, the concentrtions of phenolic lcohols did not even out in the wines ged oth in new rrels nd once-used rrels fter 15 months geing (Fig. 2(c) (e)). This mens tht these compounds re chemiclly quite stle in medium such s wine. These compounds, which imprt tosty nd spicy roms, did not rech their threshold level in the wines under study (Tle 2). Nevertheless, in complex medium such s wine, these compounds my influence wine rom t lower levels thn their individul threshold vlues y mens of dditive, synergistic, or suppressive effects (Pe rez-prieto et l., 23). The two isomers of -methyl-g-octlctone showed less differences in concentrtion thn the ove-mentioned compounds etween the wine ged in new rrels nd the wine ged in once-used rrels fter 6 months geing (cis, 5%; trns, 34%) (Fig. 3() nd ()). These compounds showed similr concentrtions in oth kinds of wine for long-term geing (12 15 months). The cisok lctone showed importnt differences in its concentrtion etween the two wines up to 9 months geing (Fig. 3()). Nevertheless, the concentrtion of trns-ok lctone ws the sme in oth wines fter 6 months geing (Fig. 3()). The decrese in the concentrtion of
T.G. Cerdán, C. Ancín-Azpilicuet / LWT 39 (26) 199 25 23 75 6 45 3 15 () 16 12 8 4 Vnillin Eugenol () 18 12 6 25 2 15 1 5 Syringldehyde Guicol (c) (d) 1.5 4-Methylguicol (e) 1.5 New rrels Once-used rrels Fig. 2. Evolution of the concentrtion (mg/l) of vnillin, syringldehyde, eugenol, guicol nd 4-methylguicol for wines ged in new nd onceused ok rrels. Ech point is the men7stndrd devition of six replictes. For ech geing period, different letters indicte significnt differences etween the smples (Po:5). these two compounds fter 9 months geing, could e ecuse their extrction diminishes nd ecuse these two compounds in the wine re in equilirium with their cid nd their corresponding ethyl ester (Wterhouse & Towey, 1994). The rtio cis/trns ws etween 5.8 nd 13.4 for the wine ged in new rrels nd etween 3.6 nd 11.1 for tht ged in once-used rrels. These vlues re similr to those found y other uthors (Wterhouse & Towey, 1994; Pollnitz, Jones, & Sefton, 1999). The cis isomer is regrded s mong the most importnt of the voltile components of okwood tht re extrcted into wine during rrel geing. This compound ws found ove its perception threshold (Tle 2) throughout the geing in oth wines. The trns isomer contriutes less to wine rom since its perception threshold is considerly greter thn tht of cis isomer (Tle 2). The concentrtion of ethylphenols, compounds formed y spoilge yest of the Brettnomyces/Dekker genus ws greter in the wines ged in once-used rrels thn in the wine ged in new rrels (Fig. 4() nd ()). The concentrtion of 4-ethylphenol incresed throughout geing in oth wines while the concentrtion of 4-ethylguicol incresed up to 9 months geing in oth types of rrel nd fterwrds it hrdly chnged. 4-Ethylphenol nd 4-ethylguicol did not rech the limit eyond which the ethylphenols cn hve negtive influence on the wine rom (Tle 2). The concentrtions of these compounds found in our smples fter 9 months geing re slightly lower thn those found y Pollnitz, Prdon, nd Sefton (2) in wines ged 8 months in Americn ok rrels (21 mg/l for new rrels nd 391 mg/l for once-used rrels). Likewise, the
24 ARTICLE IN PRESS T.G. Cerdán, C. Ancín-Azpilicuet / LWT 39 (26) 199 25 18 cis-ok lctone 45 4-Ethylphenol 12 6 () 16 12 8 4 trns-ok lctone 3 15 () 12 8 4 4-Ethylguicol () New rrels Once-used rrels () Fig. 3. Evolution of the concentrtion (mg/l) of cis-ok lctone nd trns-ok lctone for wines ged in new nd once-used ok rrels. Ech point is the men7stndrd devition of six replictes. For ech geing period, different letters indicte significnt differences etween the smples (Po:5). concentrtions of these compounds found in the wines t the end of the geing period were lower thn those found in the reused rrels (Grde-Cerd n et l., 22, ). 4. Conclusions For short-term geing, the concentrtion in the wine of most compounds from ok wood ws lower when once-used rrels were employed thn when new rrels were employed. In descending order, the compounds tht ecme most exhusted from the use of rrels were: furnic ldehydes, phenolic lcohols, phenolic ldehydes, nd ok-lctones. However, due to the evolution tht ok wood compounds undergo in wine over time, for long-term geing (12 15 months) the concentrtion of most of these compounds ws similr in oth smples, independently of the ge of the rrel. Consequently, it could e stted tht, when it comes to selecting rrel in order to ge wine, the question of whether storge is long-term or short-term ecomes relevnt. It would seem tht in the former cse, onceused rrels provide similr results to new rrels s regrds the voltile frction coming from ok wood. References New rrels Once-used rrels Fig. 4. Evolution of the concentrtion (mg/l) of 4-ethylphenol nd 4- ethylguicol for wines ged in new nd once-used rrels. Ech point is the men7stndrd devition of six replictes. For ech geing period, different letters indicte significnt differences etween the smples (Po:5). Ancín, C., Grde, T., Torre, D., & Jiménez, N. (24). Extrction of voltile compounds in model wine from different ok woods. Effect of SO 2. Food Reserch Interntionl, 37, 375 383. Boidron, J. N., Chtonnet, P., & Pons, M. (1988). Effects of wood on rom compounds of wine. Connissnce de l Vigne et du Vin, 22, 275 294. Cdhí, E., Muñoz, L., Fernández de Simo n, B., & Grcí-Vllejo, C. (21). Chnges in low moleculr weight phenolic compounds in Spnish, French, nd Americn ok woods during nturl sesoning nd tosting. Journl of Agriculturl nd Food Chemistry, 49, 179 1798. Chtonnet, P., Boidron, J. N., & Pons, M. (1989). Effect on het on ok wood nd its chemicl composition. Prt 2. Vritions of certin compounds in reltion to tosting intensity. Connissnce de l Vigne et du Vin, 23, 223 25. Chtonnet, P., Boidron, J. N., & Pons, M. (199). Mturtion of red wines in ok rrels: Evolution of some voltile compounds nd their romtic impct. Sciences des Aliments, 1, 565 587. Chtonnet, P., Duourdieu, D., Boidron, J. N., & Pons, M. (1992). The origin of ethylphenols in wines. Journl of the Science of Food nd Agriculture, 6, 165 178. Hle, M. D., McCfferty, K., Lrmie, E., Newton, J., & Swn, J. S. (1999). The influence of ok sesoning nd tosting prmeters on the composition nd qulity of wine. Americn Journl of Enology nd Viticulture, 5, 495 52. Grde-Cerdán, T., Rodríguez-Mozz, S., & Ancín-Azpilicuet, C. (22). Voltile composition of ged wine in used rrels of
T.G. Cerdán, C. Ancín-Azpilicuet / LWT 39 (26) 199 25 25 French ok. nd of Americn ok Food Reserch Interntionl, 35, 63 61. Grde-Cerdán, T., Torre-Gon i, D., & Ancín-Azpilicuet, C. (22). Chnges in the concentrtion of voltile ok compounds nd esters in red wine stored for 18 months in re-used French ok rrels. Austrlin Journl of Grpe nd Wine Reserch, 8, 14 145. Grde-Cerdán, T., Torre-Goñi, D., & Ancín-Azpilicuet, C. (24). Accumultion of voltile compounds during geing of two red wines with different composition. Journl of Food Engineering, 65, 349 356. Miller, D. P., Howell, G. S., Michelis, C. S., & Dickmnn, D. I. (1992). The content of phenolic cid nd ldehyde flvor components of white ok s ffected y site nd species. Americn Journl of Enology nd Viticulture, 43, 333 338. Miller, J. C., & Miller, J. N. (1988). Sttistics for nlyticl chemistry. London: Ellis Horwood. Morles, M. L., Benitez, B., & Troncoso, A. M. (24). Accelerted ging of wine vinegrs with ok chips: Evlution of wood flvour compounds. Food Chemistry, 88, 35 315. Office Interntionl de l Vigne et du Vin. (199). Recueil des Méthodes Interntionles d Anlyse des Vins et des Moûts. Pris. Pérez-Prieto, L. J., López-Roc, J. M., Mrtínez-Cutills, A., Prdo- Mínguez, F., & Gómez-Plz, E. (22). Mturing wines in ok rrels. Effects of origin, volume, nd ge of the rrel on the wine voltile composition. Journl of Agriculturl nd Food Chemistry, 5, 3272 3276. Pérez-Prieto, L. J., López-Roc, J. M., Mrtínez-Cutills, A., Prdo- Mínguez, F., & Go mez-plz, E. (23). Extrction nd formtion dynmic of ok-relted voltile compounds from different volume rrels to wine nd their ehvior during ottle storge. Journl of Agriculturl nd Food Chemistry, 51, 5444 5449. Pollnitz, A.P. (2). The nlysis of voltile wine components derived from ok products during winemking nd storge. Thesis, The University of Adelide, Austrli. Pollnitz, A. P., Jones, G. P., & Sefton, M. A. (1999). Determintion of ok lctones in rrel-ged wines nd in ok extrcts y stle isotope dilution nlysis. Journl of Chromtogrphy A, 857, 239 246. Pollnitz, A. P., Prdon, K. H., & Sefton, M. A. (2). Quntittive nlysis of 4-ethylphenol nd 4-ethylguicol in red wines. Journl of Chromtogrphy A, 874, 11 19. Rezin, G. H. (1981). Chemicl mechnisms of whiskey mturtion. Americn Journl of Enology nd Viticulture, 32, 283 289. Rous, C., & Alderson, B. (1983). Phenolic extrction curves for white wine ged in French nd Americn ok rrels. Americn Journl of Enology nd Viticulture, 34, 211 215. Sefton, M. A., Frncis, I. L., Pocock, K. F., & Willims, P. J. (1993). The influence of nturl sesoning on the concentrtions of eugenol, vnillin, nd cis- nd trns--methyl-g-octlctone extrcted from French nd Americn okwood. Sciences des Aliments, 13, 629 643. Spillmn, P. J., Pollnitz, A. P., Licopoulos, D., Prdon, K. H., & Sefton, M. A. (1998). Formtion nd degrdtion of furfuryl lcohol, 5-methylfurfuryl lcohol, vnillyl lcohol, nd their ethyl ethers in rrel-ged wines. Journl of Agriculturl nd Food Chemistry, 46, 657 663. Spillmn, P. J., Pollnitz, A. P., Licopoulos, D., Skouroumounis, G. K., & Sefton, M. A. (1997). Accumultion of vnillin during rrelging of white, red, nd model wines. Journl of Agriculturl nd Food Chemistry, 45, 2584 2589. Toming, T., Blnchrd, L., Drriet, P., & Duourdieu, D. (2). A powerful romtic voltile thiol, 2-furnmethnethiol, exhiiting rost coffee rom in wines mde from severl Vitis vinifer grpe vrieties. Journl of Agriculturl nd Food Chemistry, 48, 1799 182. Towey, J. P., & Wterhouse, A. L. (1996). The extrction of voltile compounds from French nd Americn ok rrels in Chrdonny during three successive vintges. Americn Journl of Enology nd Viticulture, 47, 163 172. Vnderhegen, B., Neven, H., Denen, L., Verstrepen, K. J., Verchtert, H., & Derdelinckx, G. (24). Furfuryl ethyl ether: Importnt ging flvor nd new mrker for the storge conditions of eer. Journl of Agriculturl nd Food Chemistry, 52, 1661 1668. Wterhouse, A. L., & Towey, J. P. (1994). Ok lctone isomer rtio distinguishes etween wines fermented in Americn nd French ok rrels. Journl of Agriculturl nd Food Chemistry, 42, 1971 1974. Wilkinson, K. L., Elsey, G. M., Prger, R. H., Tnk, T., & Sefton, M. A. (24). Precursors to ok lctone. Prt 2: Synthesis, seprtion nd clevge of severl -D-glucopyrnosides of 3- methyl-4-hydroxyoctnoic cid. Tetrhedron, 6, 691 61.