A review of microoxygenation application in wine

Transcription

1 Review article Received: 15 October 2012 Revised: 21 December 2012 Accepted: 3 January 2013 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI /jib.51 A review of microoxygenation application in wine R. Ertan Anli 1 * and Özge Algan Cavuldak 2 Oxygen has a fundamental role in the vinification process and occurs in the various stages, particularly during the fermentation and aging of wines. Phenolic compounds, such as oxygen, are relatively important in wine quality. Among polyphenols, anthocyanins and tannins are the most important compounds since they contribute to the organoleptic characteristics of wines, particularly colour and astringency. During wine-making and aging, phenolics extracted from grapes gradually change owing to biochemical reactions, which result in a decrease in astringency as well as colour stabilization. Therefore, addition of a measured amount of oxygen, referred to as a microoxygenation process, was proposed to improve wine quality by accelerating these transformations of phenols. In a microoxygenation process, it is assumed that modification of phenolic compound reactions by oxidation should result in more coloured and less astringent products. In this article, the role of oxygen, phenolics and microoxygenation application in wine technology has been reviewed. Copyright 2013 The Keywords: microoxygenation; oxygen; phenolics; wine 368 Introduction The microoxygenation (MOX) technique, which promotes changes in the phenolic structure of a wine, is a new technology in wine production that pays great attention to managing the role of oxygen in wine-making (1,2). Phenolic components from the grape are the principal substrates of wine oxidation. The phenolic compounds and the reaction products are major wine constituents and are responsible for variations in wine types (3). This technique was developed in France by Patrick Ducournau at the beginning of the 1990s, then Ducournau and Laplace registered a patent for the MOX method, and it has been gaining popularity all over the world (4,5). Although this process is thought to be new and revolutionary, it is actually an enhancement of the oak barrel aging process (6). In order to oxygenate wine, the usage of gaseous oxygen is something of a two-edged sword. It can be highly beneficial when well controlled, but it can also damage wine (7). Oxygen takes an important role in the vinification process. Oxidation, condensation and polymerization reactions, in which phenolic compounds are involved, are oxygen-dependent (8). Throughout maturing of the wine in barrels, oxygen input may have a structuring effect by promoting colour stabilization, disappearance of reduction taste and reduction of vegetal characteristics. However, management of oxygen input has never been controlled during these conventional maturation processes (9). When the amount of additional oxygen is excessive, it can result in negative effects such as phenol oxidation, perception of tannin dryness, higher astringency, loss of wine freshness, oxidized aroma and adverse microbial activity. Therefore, the addition of oxygen must be controlled (1). Microoxygenation, which is a new vinification method using stainless steel tanks and a monitored oxygen micro-supply, is frequently applied (10) in order to simulate the aging characteristics of barrels (11). The aim of the microoxygenation process is to manage the rate and result of the oxygen-requiring reactions with the aim of desirable changes in wine texture and aroma (12). Oxygenation of wine, which is defined as the diffusion of air or oxygen into the wine, is an authorized oenological practice in the International Code of Oenological Practices of the OIV (13). The role of oxygen in wine Oxygen has a fundamental role in wine technology (10).Itplaysan important role in the different processes that take place during wine-making and the aging of wine (1,14 16). Oxygen can affect the quality of wine, either positively or negatively (15). Generally, slow oxygenation will allow the wine to develop in complexity, while any rapid oxidation will cause a quality loss (10). Oxygen causes oxidation of phenolic and volatile compounds, whereas an adequate dose improves the organoleptic characteristics of the wine (17). Oxygen has an influence on the phenolic composition and also has an indirect effect on some sensorial characteristics, such as colour, aroma and astringency, all of which determine wine quality. This is due to the important role that oxygen plays in oxidation, condensation and polymerization reactions in which phenolic compounds are involved (16,18). The main compounds responsible for oxygen consumption are polyphenols (10). In other words phenolics, which are responsible of the wine quality (19), are the principal substrates of wine oxidation (1,20). The phenolic concentration is an indicator for oxidation in wine, namely, higher phenol-content wines are able to take higher concentrations of oxygen (16). The addition of oxygen to wine leads to polymerization of certain phenolic compounds, * Correspondence to: R. Ertan Anli, Ankara University, Department of Food Engineering, Diskapi, Ankara, Turkey. anli@eng.ankara.edu.tr 1 Ankara University, Department of Food Engineering, Diskapi, Ankara, Turkey 2 Bulent Ecevit University, Caycuma Vocational School of Higher Education, Caycuma, Zonguldak, Turkey J. Inst. Brew. 2012; 118: Copyright 2013 The

2 Microoxygenation application in wine such as anthocyanin and flavanol moieties. This polymerization occurs owing to the formation of H 2 O 2, which is a strong oxidant and oxidizes ethanol to yield acetaldehyde. It forms a bridge between phenolic molecules and leads to polymerization reactions (21,22). Oxygen can be dispersed into the wine during various stages, such as pumping, racking and barrel aging (10). In the winemaking process, the contact of oxygen is regarded as a critical point since oxygen can greatly affect wine quality (23). It is essential in the polymerization of polyphenolic compounds, especially in the early stages of maturation. Polymerization reactions can provide better colour stability and intensity at wine ph producing stable forms of anthocyanins that resist decolourization by sulphur dioxide. The products are pigmented polymers, which are coloured forms and stable over time (12). Consequently, these reactions affect the sensorial characteristics of the finished wine, such as producing coloured compounds and decreasing the astringency, and thus affecting both flavour and colour. The role of phenolics in wine Polyphenolic compounds, particularly anthocyanins, flavanols and other flavonoids have a fundamental role in wine quality (24 26). They identify sensorial characteristics of wines, especially red ones. Organoleptic characteristics of red wines depend on the amount, type, composition and distribution of phenolic pigments (27). Wine phenolic composition is conditioned by the grape used and wine-making processes, which determine the extraction of phenolics into the must and their further stability in wine (28 31). The changes in the phenolic compounds extracted from the grapes provide colour evolution during wine-making. The natural grape anthocyanins, which are responsible for the purple-red colour of young red wines, are transformed into more stable pigments and these forms generate the brick-red colour of more aged wines (32 34). From the point of sensorial characteristics of a wine, the first one noticed is colour. The principal compounds in a young red wine that are responsible for its colour are the anthocyanins. A general scheme of anthocyanins can be seen in Fig. 1. During aging and storage of red wine, many changes occur. The degradation and transformation of free anthocyanins into more stable coloured pigments result in the new colour of enhanced wines (35 37). Namely, during wine storage, anthocyanins are slowly converted into new pigments by condensation with other phenolic compounds (38 41). Condensed tannins (proanthocyanidins) are responsible for the astringency and bitterness of the wine (42 46). Proanthocyanidins are oligomeric and polymeric flavan-3-ols based on various units. These are mainly (+)-catechin, ( )- epicatechin, ( )-epicatechin-o-gallate and ( )-epigallocatechin, which are linked to each other by C4 C8 or C4 C6 B-type bonds (47,48). The general scheme of proanthocyanidins is given in Fig. 2. In the wine-making and aging process, phenolic compounds are quickly transformed into several pigments via various types of reactions (49 53). These reactions are as follows: direct condensation reactions between anthocyanins and tannins, aldehyde-mediated condensation reactions between anthocyanins and tannins, cyclo-addition reactions, leading to the formation of pyranoanthocyanins, enzymatic and chemical oxidation reactions (4,42,54). Condensation reactions of flavanols (T), directly with other flavanols and with anthocyanins (A), lead to two kinds of products, denoted A T and T A, according to the position of the anthocyanin moiety (18,55 57). Acetaldehyde-mediated condensation reactions of flavanols with other flavanols and with anthocyanins result in more stable compounds (42,56,58 60). Figure 3 shows the structure of pigments derived from the acetaldehyde-mediated condensation between anthocyanins and catechins. The detection of (+)-catechin ethyl-bridged dimers in wine, of ethyl-bridged (epi)-catechin dimers and trimers and of (epi)-catechin-ethyl-malvidin-3-glucoside in model wine solutions showed the existence of this condensation reaction in red wines (18,21,61 67). Cycloaddition reactions of anthocyanins and/or flavanols with other lower-molecular-weight compounds, such as pyruvic acid, vinylphenol or glyoxylic acid, to form new pigments that maintain wine colour intensity for longer periods, have been established (18,68 75). The structure of the pyranoanthocyanins vinylphenol adduct is given in Fig. 4. Through the reaction between anthocyanin pyruvic acid adducts and vinyl-flavanols, new types of anthocyanin pigments have been detected in red wines (16,76 79). These molecules are more resistant to ph changes and SO 2 bleaching and so they can provide higher colour stability (80 82). Figure 1. General scheme of anthocyanins (25). Figure 2. General scheme of proanthocyanidins (25). 369 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib

3 Figure 3. Structure of pigments derived from the acetaldehyde-mediated condensation between anthocyanins and catechins (65). The chemical reactions of phenolic compounds during red wine aging form new coloured and uncoloured oligomers (83) and result in the disappearance of much of the bitterness, astringency and harshness in the wine (28). In other words, a young red wine that is harsh, astringent and even bitter becomes softer and less astringent during oak barrel aging (16). The other main source of phenolics is oak phenolics that come from oak during aging. The composition of the oak has a fundamental effect on wine quality. During aging in oak barrels, the composition of the wine undergoes changes because of the addition of phenolic compounds and other molecules extracted from the wood (24,84 86). The main extractable oak wood components are polyphenols, ellagitannins and volatile compounds (87). Various kinds of woods have been used and low-molecular-weight phenolic compounds such as gallic acid, ellagic acid, ferulic acid, scopoletin, acetovanillona and ethyl vanillin have been quantified in aged wine brandies. These compounds can be regarded as chemical markers according to the botanical species of the wooden barrel (88). Therefore, the knowledge of the chemical composition of woods to be used for wine aging is a significant factor that affects the choice of the wood (89). Nevertheless, the barrel-aging process has disadvantages such as a longer keeping time, which increases cost and labour. (90). R. E. Anli and Ö. A. Cavuldak complex aroma, colour stability and spontaneous clarification, generally oak barrels are used in the aging of wine (91,92). Microoxygenation has been thought to be an alternative or complementary method for accelerating the aging process in barrels. As a result, it may provide some of the improvements of barrel aging in wine quality, but with less time and a lower cost (93). Microoxygenation allows the introduction of controlled, small and continuous amounts of oxygen into wine via a porous diffuser (1,94). The diffuser permits a slow and continuous flow rate of a few millilitres of oxygen per litre of wine per month, allowing the wine phenols to consume the oxygen without acquiring negative characteristics (95). The controlled amount of oxygen is transferred from oxygen supplier to wine tank via MOX equipment in order to adjust the volume of oxygen. The oxygen gas that is transferred into the tank is observed as bubbles. These bubbles disperse into the wine rapidly. A schematic diagram of the microoxygenation process is shown in Fig. 5. It is necessary to take care with the bubbles that dissolve into the wine when microoxygenation is applied, to prevent them from reaching to the top of the tank. As a result of this, the tank needs to be at least 2.2 m tall, to make the dissolving of the bubbles in the wine easier (16,22,62). The oxygenation dosage has to be carefully managed to obtain the desired effect. Most important is that the rate at which oxygen is supplied to the wine is equal to or lower than the rate at which it is consumed by the wine, in order to avoid oxygen accumulation (4,17). The oxygenation rate and the applied oxygen depend on the phenolic composition, volatile sulphides and also the ability of the wine to consume this oxygen. Oxygen rate is indirectly related to the concentration of polyphenolic compounds and is determined by tasting (96). Wines that lack phenolics, which are substrates for polymerization reactions, cannot take much oxygen. These wines are not preferred for treating with oxygen. Besides, if microoxygenation is applied to these wines, in any case, it is the best to do this after the malolactic fermentation and with low rates. The ideal Application of microoxygenation Aging in wood barrels, which improves sensorial characteristics of wine, traditionally has been applied to achieve high-quality wines (90). For the purpose of the positive effects, such as 370 Figure 4. Chemical structure of pyranoanthocyanin-vinylphenol adducts (82). Figure 5. Schematic diagram of the microoxygenation process. wileyonlinelibrary.com/journal/jib Copyright 2013 The J. Inst. Brew. 2012; 118:

4 Microoxygenation application in wine wines for microoxygenation are those rich in anthocyanin and phenolic materials (12). There may be several practical difficulties in microoxygenation applications. For instance, if oxygen is introduced too quickly, oxidation may occur, and browning and precipitates may form. Oxidation may also cause a comprisingly high acetaldehyde level. Acetaldehyde at sensory threshold levels negatively affects wine quality, especially wine flavour, and consumers may even consider the wine to have spoiled. In order to determine the appropriate endpoint for the microoxygenation process, monitoring acetaldehyde levels should be used as a practical method (93). There are some parameters, including dissolved oxygen rate (97), turbidity, temperature and free sulphur dioxide measurements, that should be monitored during the process. Tasting is also important in terms of determining dose and timing of oxygen. If the oxygen flow rate is chosen appropriately and dissolved oxygen levels do not increase during microoxygenation, the process is conducted properly; otherwise excessive oxygen may cause microbial spoilage in wine (12). Free sulphur dioxide level is another important parameter during microoxygenation. A decrease or increase of the free SO 2 level is indicative of how the wine is responding to microoxygenation (6). The other essential measurement is temperature. The microoxygenation process works best at between 14 and 17 C; too high a temperature adversely affects the dissolved oxygen levels in the tank. Increases in temperature can result in poor solubility of oxygen; decreases in temperature can cause accumulation of oxygen in the headspace of the tank, and also chemical reactions such as polymerization and condensation can take place too slowly during microoxygenation (12,16,98,99). The clarity or turbidity of the wine is also significant. Thus, wines should have some degree of clarification for efficient microoxygenation. Wines should be ideally below 100 NTU; above this level, wines can be treated, but monitoring will be more difficult (12,99). A number of scientific studies are available in the literature regarding microoxygenation treatments in wine-making. Some of these are summarized in Table 1. Most of the studies have been published on the effect of microoxygenation on the phenolic composition and colour of wine (2,18,95,96, ). Some of them have also been concerned with the aromatic and volatile composition (17,90,101,106,108, ). A few of these approach the measuring of the concentration of oxygen dissolved in the wine during the microoxygenation treatments (90,113). Some microoxygenation studies have investigated the effect of MOX on the level of single bioactive phenolics and the antioxidant profile (8,100,106). Others assess whether MOX could mimic oak barrel aging (114) or evaluate the effect of MOX on the microbial composition of the wine (22). The microoxygenation process in tanks with various oak products can be applied in order to simulate oak barrels. Wines that are produced by this combination process are similar to those aged in oak barrels. Many researchers have studied the effect of microoxygenation and oak chips or wood tablet treatment on wine colour and phenolic compounds (6,22,113, ), and on volatile compounds and sensory characteristics of the wine (22, ). Furthermore, also the effects of using yeast lees, chips and microoxygenation on the wine s aromatic composition and sensory profiles (122) and on colour and phenolic composition have been studied(123). A general trend in analytical results on phenolic composition of microoxygenation-treated wines is a decrease in the concentration of monomeric anthocyanins (2,6,18,96,100, ,106,108,109,113,114,118,123) concomitant with higher concentrations of pyranoanthocyanins, ethyl-bridged compounds and polymeric anthocyanins than control wines (2,6,18,22,95,96, ,106,108,113,114,118). Unexpectedly, in one study the MOX wine had a higher free anthocyanin concentration than the control wine. One alternative explanation for such an increase could be the instability of the anthocyanin ethyl flavanol compounds, which may undergo cleavage of the ethyl bridge and allow free anthocyanins and structural rearrangements (65,101). Differences were also observed in the chromatic characteristics. There was a significant increase in concentrations of pyranoanthocyanins, derived pigments and ethyl-linked compounds, which demonstrate changes in colour characteristics, in oxygenated wines as opposed to the control wines (18). The reactions that lead to the formation of higher molecular weight compounds also stabilize wine colour, forming new coloured compounds stable to changes of SO 2 and ph. The comparison between the control and microoxygenated wines, whether stored in oak barrels or bottles, demonstrated that microoxygenated wines maintained higher concentrations of compounds resistant to SO 2 discoloration (2). It has been shown that microoxygenation can provide more intense colour encouraged by compounds resistant to SO 2 discolouration (104). The CDRSO 2 parameter, which defines the colour owing to pigments resistant to SO 2 bleaching, is increased in microoxygenated wines (2, ). The CDRSO 2 parameter, which is useful for monitoring the effect of microoxygenation on the improvement of the colour of wines, could be used as an analysis in the production of wines with the microoxygenation process (104). Microoxygenation favours the formation of new polymeric pigments, thus MOX wines gain colour stabilization (95,99,100,104,107,113,114,117,118,123) owing to the higher concentrations of pyranoanthocyanins and adducts formed by reaction between anthocyanins and flavan-3-ols mediated by acetaldehyde. The microoxygenated wines show a higher colour intensity than untreated wines (2,6,18,22,95,96,100, ,108,113,114,117) in contrast to the findings of a few studies (101,120). Microoxygenation promotes reactions that result in a greater formation of ethyl-linked compounds and pyranoanthocyanins (102). In time, the initial wine composition that had high concentration levels of free anthocyanins gradually disappeared and more stable structures such as pyranoanthocyanins collected. Oxygen exposure increased the anthocyanin degradation and favoured reactions involving acetaldehyde, leading to ethylbridged compounds. Acetaldehyde is formed from the oxidation of ethanol by phenolic compounds during maturation and also yeast metabolism during fermentation (12). It is regarded as a key MOX-responsive element generated by the oxygencatalysed oxidation of ethanol in the presence of wine phenolics. It can be thought of as a link between oxygen and the phenolics (18,124). During microoxygenation, the formation of acetaldehyde from ethanol oxidation would thus favour the ethyl bridges between flavanols and between flavanols and anthocyanins. Nevertheless, the rate of these reactions is ph-dependent; also the concentration of the final compounds is significantly influenced by the ph of the wine (125). In a study, ethyl-linked pigments, B-type vitisins and polymeric pigments were higher when the wine ph was more acidic (126). 371 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib

5 R. E. Anli and Ö. A. Cavuldak Table 1. Summary of studies on microoxygenation treatment in wine making Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Cano-Lopez et al., 2007 (2) Monastrell Effect of MOX application and maturation in oak barrels or bottles on phenols and colour of Monastrell wine After AF (pre + post MLF) (1) Control: No MOX #Monomeric anthocyanins (2) Low dose MOX "Tint with both maturation Pre-MLF: 5 ml/l/month + post-mlf: 3 ml/l/month "Colour intensity with MOX (3) High dose MOX #Colour intensity in bottle maturation Pre-MLF: 10 ml/l/month + post- MLF: 5 ml/l/month 1 month after MOX: aging in bottle/in oak barrel during 6 months "Colour intensity in oak barrel maturation #Total wine colour with both maturation "CDRSO2 in MOX wines #Ethyl-linked compounds with both maturation Oak-matured control wines is similar to bottled microoxygenated wines (chromatic characteristics) McCord, 2003 (6) Cabernet Sauvignon Effect of MOX and toasted oak products with and without MOX on the aging of Cabernet Sauvignon wine and evaluation of various analytical methods to provide an effective and useful tool to monitor the maturation of wine undergoing MOX Post-MLF Aging in tanks #Monomeric procyanidins (1) Control: no oak/no oxygen #Total anthocyanin (2) Staves only/no oxygen "Colour intensity (3) Segments only/no oxygen "Perceived softening of wine (4) Oxygen only/no oak #Free mercaptan (5) Staves and oxygen!dimethyl sulfide (6) Segments and oxygen. #Methyl and ethyl mercaptan (with MOX) MOX: 10 ml/l/month 1 month; "Polymeric phenolics (with MOX 5 ml/l/month 4 months and also with oak segments) "Polymerization of anthocyanins (with O2 and oak segments) Rivero-Perez et al., 2008 (8) Tinta de Toro Effect of MOX on the antioxidant profile of Spanish red singlevariety wines of different ages Pre-MLF (1) Control!Antioxidant capacity or scavenger activity Mencía (2) MOX: ml/l/month-... Tempranillo Both aging in oak barrels Tinta del País (4 24 months) " Inhibitory capacity of DNA-dam age (especially in young MOX wines vs aged wines) # Inhibition of lipid peroxidation Varietal effect (Tinta del pais more influenced by MOX) (Continues) 372 wileyonlinelibrary.com/journal/jib Copyright 2013 The J. Inst. Brew. 2012; 118:

6 Microoxygenation application in wine Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Ortega-Heras et al., 2008 (17) Tinta de Toro Effect of MOX on the volatile composition of two red singlevariety wines during two successive vintages Pre-MLF (1) Control!Fruity notes Mencía (2) MOX: "Fusel alcohols "Fatty acids (slight) Mencia (first and second vintage): 60 ml/l/month 10 days (first dose) + 30 ml/l/month 8 10 days (second dose) Tinta de Toro: (first and second vintage): 50 ml/l/month 10 days (first dose) ml/l/month 10 days (second dose) Both aging in oak barrels (12 months) Varietal and vintage effect for the result of MOX on some volatile compounds Atanasova et al., 2002 (18) Cabernet Sauvignon (%60) + Tannat(%40) Influence of MOX on colour and phenolic composition of red wine After AF (1) Control: no O2 "More stable structures (2) MOX: 5 ml/l 7 months "Pyranoanthocyanins "Ethyl-bridged compounds "Derived pigments "Colour density #Free anthocyanins #Astringency Du Toit et al., 2006 (22) A. Cabernet Sauvignon Effect of MOX on the phenolic composition, quality and aerobic wine spoilage microorganisms of red wines A and B: just after MLF A: MOX: 0/1.5 and 3 mg/l/month with oak staves B. Red blend B: MOX: 0 and 4 mg/l/month C. Pinotage C and D: 7 months with oak staves D. Shiraz after MLF C: MOX: 0/1.5 and 3 mg/l/month with oak staves + barrel maturing D: MOX: 0 and 3 mg/l/month with oak staves "Colour density "Polymeric phenols "Polymeric pigments #Catechin and procyanidin B 1 "Acetic acid bacteria!volatile acidity "Brettanomyces "Barnyard/medicinal flavours(in older wine) Castellari et al., 2004 (23) Merlot Evaluation of the influence of Cabernet Sauvignon single technological practices (racking, filtration, centrifuga Corvinone tion, maturation and MOX After AF (during storage) Maturation in tanks or wooden barrels (4 6 months) Sangiovese (1) MOX 1 : 1/2 or 5 ml/l/month (2) MOX 2 : 3 ml/l/month Montepulciano during storage in stainless steel tanks) on the level of dissolved O 2 in wines Rondinella Chardonnay Pinot Trebbiano MOX increase the concentration of dissolved O 2 in wines matured in stainless steel tanks up to levels comparable with those observed in wines matured in small wooden barrels. Only when MOX (5 ml/l/month) was supplied, the median level of dissolved O 2 in wines was comparable to the values measured in wines stored in small wooden barrels (Continues) 373 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib

7 R. E. Anli and Ö. A. Cavuldak Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Hernandez-Orte et al., 2009 (90) Tempranillo Influence of factors such as the Cabernet Sauvignon MLF vessel or MOX process (a) MLF vat before maturation in (b) MLF barrel barrels on the volatile (c) No MLF barrel composition and sensorial (2) MOX: 60 ml/l/month 15 days composition of wine (a) MLF MOX vat (b) MLF MOX barrel (c) No MLF MOX barrel All barrel maturation (8 months) Pre-MLF (1) Control MOX significantly affected more compounds and aroma notes in CS wines than in wines of the TE varietals (varietal effect) "Furfural (only in TE MOX wines) #Volatile phenols (with MOX) If MLF in barrels rather than steel vats "Sweeter wines " Wood and toasty notes If MLF in steel vats, #Alcohol notes #Reduction notes Perez-Magarino et al., 2007 (95) Mencia Effects of MOX applied before Pre-MLF (1) Control: no MOX #Total phenols Tinta de Toro MLF, on colour stabilization (2) MOX: total O2 for 3 vintages #Total anthocyanins Tinta del Pais and phenolic composition of Mencia: ml/l days "Polymeric anthocyanins Tempranillo different single varietal red Tinta de Toro: ml/l "Colour intensity wines for three vintages days "Colour stability Tinta del Pais: ml/l days Tempranillo: ml/l days #Red % "Blue tonality MOX effect on colour stability independent of variety and vintage factors Kovacevic Ganic et al., 2008 (96) Plavac mali Influence of MOX on the phenolic composition and colour of red wine Pre-MLF (1) Control #Total phenols (slight) (2) MOX: 40.1 ml/l (total) #Total anthocyanins (slight) 39 days #Monomeric anthocyanins "Polymeric anthocyanins "Colour intensity #Colour hue (slight) Castellari et al., 2000 (100) Sangiovese Influence of controlled levels of MOX of red wine on colour and composition during storage, emphasizing its effect on the level of single bioactive phenolics During maturation (6 months) (1) Control: no O2 #Total phenolic compounds (2) Oxy-A: 8 mg/l O 2 "Red polymeric pigments every 2 months (60 days) "Red wine colour (3) Oxy-B: 10 ml/min every "Colour stability month (30 days) "Colour density (in Oxy-B) #Single anthocyanins (Continues) 374 wileyonlinelibrary.com/journal/jib Copyright 2013 The J. Inst. Brew. 2012; 118:

8 Microoxygenation application in wine Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Del Carmen Llaudy et al., 2006 (101) Cabernet Sauvignon Effect of MOX on phenolic compounds, astringency and colour of red wine Before oak aging (1) Control: aging in oak barrels (8 months) + in stainless steel tanks (3 months) (2) MOX: 3 mg/l/month 3 months + aging in oak barrels (8 months) #Colour intensity "H* (colour hue) "L* "MDP "Ethyl-bridged pigments "Free anthocyanins "Combined anthocyanins "Colour stability #Astringency "Wood aromas "Toasting, spices, coffee aromas Cano-Lopez et al., 2006 (102) Monastrell Effect of MOX on anthocyanin profile and chromatic characteristics of Monastrell wine After AF (pre- + post- MLF) (1) Control: no MOX #Monoglucoside anthocyanins (2) Low-dose MOX: 5 ml/l 20 days (pre-mlf) + 3 ml/l 1 month (post-mlf) ml/l 2 weeks (1 month later) (3) High-dose MOX: 10 ml/l 20 days (pre-mlf) + 5 ml/l 1 month (post-mlf) ml/l 2 weeks (1 month later) "Vitisins (some of pyranoanthocyanins) "Ethyl-linked compounds "Colour intensity (especially with high dose MOX) "CDR SO2 Cano-Lopez et al., 2008 (103) Monastrell (three wines of different phenol contents) Effect of MOX on colour and anthocyanin-related compounds of wines with different phenolic contents After AF (pre- + post- MLF) (1) Control #Monomeric anthocyanins (2) MOX for W1,W2,W3: "Ethyl-linked compounds Pre-MLF: 10 ml/l/month "Anthocyanin-derived pigments 23 days (W1) Pre-MLF: 10 ml/l/month 43 days (W2, W3) Post-MLF: 3 ml/l/month 2 months ml/l/month... (W1,W2,W3) "Colour intensity "MDP, overoxygenation (in lowest phenolic content W1) "CDRSO 2 Gonzalez-del Pozo et al., 2010 (104) Cabernet Sauvignon Short- and long-term influence of MOX on the chromatic characteristics and anthocyanic composition of wines Pre- + post-mlf (1) Control #Total anthocyanins (2) MOX: #Monomeric anthocyanins Pre-MLF: 15 mg/l (total) 3 weeks "Colour intensity 90 mg/l/month 3 days + 10 mg/l/month 17 days Post-MLF: 6 mg/l (total) 3 months 2 mg/l/month 3 months Both bottle and barrel aging (12 months) Both bottle aging (8 months) "Colour stability "CDRSO2 (Continues) 375 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib

9 R. E. Anli and Ö. A. Cavuldak Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Rayne et al., 2011 (105) Merlot, Cabernet Sauvignon Investigate whether shortduration MOX immediately after fermentation and prior to MLF and oak barreling results in a suite of UV visible based optical and compositional descriptors Pre-MLF (1) Control: no MOX Merlot Cabernet Sauvignon (2) MOX: "Cl "Cl Merlot: 16.1 ml/l (total) 15 days!tint "Tint (24 34 ml/l/month 15 days) Cabernet Sauvignon: 13.8 ml/l (total) 14 days (2 44 ml/l/ month 14 days) #% of yellow "%of yellow Both barrel aging (5 6 months)! % of red #%of red! % of blue "%of blue "TCP! TCP "WC! WC!TMA! TMA " CDRSO2 " CDRSO 2 " CAW " CAW De Beer et al., 2008 (106) Pinotage Effect of oxygenation during maturation on the phenolic composition, total antioxi dant capacity (TAC), colour and sensory quality of Pinotage wines After AF (No MLF) (1) Control: No MOX #Monomeric anthocyanins (2) Low dose MOX: (especially in high-dose MOX) 2.5 mg/l/month 2/4/6 months (in discrete doses) (3) High dose MOX: 5.0 mg/l/month 2/4/6 months (in discrete doses) "Fullness "Polymeric anthocyanins (especially in high-dose MOX) #Total flavonol content!astringency #TAC #Berry/plum intensity (especially in high-dose MOX) "Gallic acid (especially in high-dose MOX) "Sensory colour acceptability #L* (lightness), C*(chroma), a* (red/green chromacity) #Sensory overall quality (especially in high-dose MOX) Cejudo-Bastante et al., 2011 (107) Cencibel Evaluation of the effects of MOX and later storage on the colour parameters, phenolic and volatile composition and subsequently descriptive sensorial characteristics Pre-MLF (1) Control: no MOX "Anthocyanin-derived red wine (2) MOX: 10 ml/l/month 20 days pigments + Both storage in stainless steel "Colour stability tanks (5 months) "Orange hues (b*) #Red fruit notes "Astringency score "Complexity (plum/currant) "Liquorice and spicy values (Continues) 376 wileyonlinelibrary.com/journal/jib Copyright 2013 The J. Inst. Brew. 2012; 118:

10 Microoxygenation application in wine Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples #Green taste, acidity and bitterness values "Succinic acid derivatives and long-chain esters #Short chain esters, acetates and C6-alcohols Sanchez-Iglesias et al., 2009 (108) Tinta de Toro (Tempranillo) Evaluation of phenolic composition, especially of anthocyanins and colour, astringency and tannins during MOX before barrel aging; also evaluation during aging depends on barrel type (four different oak barrel types) Pre-MLF (1) Control: no MOX + aging in oak barrels (4 type of oak) 12 months (2) MOX: first vintage: 36 ml/l/month (total) 20 days second vintage: 41 ml/l/month (total) 20 days + Aging in oak barrels (4 types of oak) 12 months #Total anthocyanins "Polymeric anthocyanins #Monomeric anthocyanins "Colour intensity "Blue % #Red % and Yellow %!Tonality Astringency and colour (no difference at sensory level) These results show that effects of MOX decrease as wine ages in oak barrels Wood types only affect anthocyanin fraction and so wine colour Tao et al., 2007 (109) Merlot Changes in a range of polyphenol measures were recorded, which showed that the concentration of SO2 had a marked effect on wine development During storage (1) Control: no MOX + no SO 2 #Monomeric anthocyanins No MOX + 50 mg/l SO 2 "Nonbleachable pigments No MOX mg/l SO 2 "Size and red colouration of No MOX mg/l SO 2 proanthocyanidin extract (especially wines with low SO 2 ) (2) MOX1:10 ml/l/month 16 weeks + no SO 2 MOX2: 10 ml/l/month 16 weeks + 50 mg/l SO 2 MOX3: 10 ml/l/month 16 weeks mg/l SO 2 MOX4: 10 ml/l/month 16 weeks mg/l SO 2 Changes suppressed in wines with 200 mg/l SO 2 or control SO 2 regulates polymeric pigments and tannin structure and so astringency Nevares et al., 2009 (113) Tinto del Pais Evolution of the dissolved oxygen content in red wines during alternative accelerated aging During aging Aging (9 months) # Free anthocyanins (1) Control # Red tonalities (2) Chips (level of toasting light, medium, high) + MOX ( ml (l/month) in tanks " Brown tones " Volatile acidity " Combined forms " Red colour intensity (Continues) 377 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib

11 R. E. Anli and Ö. A. Cavuldak Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples "Colour stability (especially with chips at high toast level) Cano-Lopez et al., 2010 (114) Monastrell Check whether MOX could mimic oak barrel aging as regards the effect on wine colour Post-MLF (1) Control (in stainless steel tank all the time) (2) MOX (3 ml/l/month 3months)+ Bottle aging (6 months) (3) Oak barrel maturing (3 months and 6 months)+ #Monomeric anthocyanins (both MOX and oak matured wines) "Vitisin related pigments (both MOX and oak matured wines) "Colour intensity (both MOX and oak matured wines) Bottle aging (6 months) #Total phenols (MOX) "Total phenols (oak barrel aging) "Colour stability (after 6 months in oak matured wines via MOX wines) Rudnitskaya et al., 2009 (115) Shiraz, three vintages Influence of MOX and maceration with oak chip treatments on wine composition Post-MLF (1) Control Vintage most important factor (2) MOX: 2 ml/l/month with respect to the phenolic (3) Maceration with oak chips (4) MOX + maceration with oak chips (5) Oak barrels composition of wine #Flavylium and % flavylium in cation form "Acetic acid!volatile acidity "All CIE-Lab coordinates except a Changes in the phenolic compounds; the ET based on the potentiometric chemical sensors is a promising analytical tool for rapid and on-line wine analysis Perez-Magarino et al., 2009 (116) Mencia, Tinta del Pais The combined effect of different chips and the application of MOX before malolactic fermentation on colour and phenolic composition of red wines Pre-MLF (1) Control: no MOX Grape variety and especially MOX (2) MOX: Mencia: 25 ml/l (total) 17 days Tinta del Pais: 31 ml/l (total) 20 days (3) Oak chips maceration + O2 (2 ml/l/month 1 month): Control + 4 types of chips (origin and toasting) MOX + 4 types of chips (origin and toasting) have more influence than type of chips on phenols and colour (Continues) 378 wileyonlinelibrary.com/journal/jib Copyright 2013 The J. Inst. Brew. 2012; 118:

12 Microoxygenation application in wine Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Cejudo-Bastante et al., 2011 (117) Petit verdot Effects of MOX before MLF and oak chip treatments on the colour characteristics, phenolic compounds related to the colour of red wine, volatile compounds, and sensory characteristics of Petit verdot red wines Pre-MLF (1) Control: no MOX #Monomeric anthocyanins (2) MOX: 45 ml/l/month 20 days "Polymerization % +Both oak chips treatment "Pyranoanthocyanins especially (25 days) A-type vitisins "Colour intensity "Colour stability "Orange hues (b*) "Red fruit attributes "Plum/currant attributes New attributes, such as nutty and tobacco notes #Bitterness and astringency with MOX, but differences were lower between control and MOX wines after MLF and chips treatment Cejudo-Bastante et al., 2011 (118) Merlot Effects of MOX before malolactic fermentation and, subsequently, oak chip treatments on the colour parameters, phenolic, volatile composition and sensory characteristics of the wine Pre-MLF (1) Control: no MOX #Monomeric anthocyanins (2) MOX: 30 ml/l/month 20 days + oak chips treatmant (25 days) #Flavan-3-ols "Pyranoanthocyanins (B-type vitisins) "Colour stability #a* #b* #Tonality "Red fruits and spicy attributes "Plum/currant odour "Nutty/sweet fruit flavor #Astringency #Wood attributes Canas et al., 2009 (120) Lourinha wine brandy Compare alternative aging systems (stainless-steel tanks with wood tablets, with and without oxygenation) with the traditional aging system of wine brandies (wooden barrels) based on their effects during the first year of aging During aging (1) Aging in barrels "Total polyphenol index (with (2) Aging in stainless-steel tanks oxygenation) with wood tablets #Colour intensity (with (3) Aging in stainless-steel tanks with oxygenation) wood tablets and oxygenation (4.5 mg/l) #Sensory analysis (with oxygenation) (Continues) 379 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib

13 R. E. Anli and Ö. A. Cavuldak Table 1. (Continued) Author(s) and date Grape variety Object of MOX treatment Timing Dose and period Some findings for MOX samples Rodriguez Bencomo et al., 2008 (121) Mencia Effect of MOX and wood factors such as botanical and geographical origin and toasting degree along with contact time on the extraction of volatile compounds present in oak chips Pre-MLF (1) Control: no MOX (pre-mlf) + chip maceration (4 types origin and toast degree) + MOX (2 ml/l/month 28 days) (post-mlf) (2) MOX: 44 ml/l/month (25 ml/l total O2) 17 days (pre-mlf) + chip maceration (4 types origin and toast degree) + MOX (2 ml/l/month 28 days) (post-mlf) No significant difference between control and MOX wines but the type of the chip influenced the final concentration of volatile compounds of the wine Arfelli et al., 2011 (122) Sangiovese Influence of oak chips, yeast lees and MOX on wine aromatic composition and sensory profile, evaluating the contribution of these techniques on wine aging and bottle storage Post-MLF Aging (90 days) "Wood aroma (with chips) (1) Control #Bitterness and astringency (2) Control + oak chips (with MOX also especially (3) Control + oak chips + MOX (3 ml/l/month) (4) Control + oak chips + yeast lees + MOX (9 ml/l/month) Bottle storage (5 months) adding with lees) "Vanilla perception (in C + chips + lees + MOX wines) For sensory characteristics, the preferred wine is C + chips + lees + MOX wines Sartini et al., 2007 (123) Sangiovese Influence of chips, yeast lees and MOX techniques at the end of aging and during bottle storage on colour and phenolic composition of a Sangiovese wine Post-MLF Aging (3 months) "Colour stability (especially in chips + lees + MOX wines) (1) Control "Red polymeric colour (2) Control + chips (in MOX wines) (3) Control + chips + MOX #Monomeric anthocyanins (in (3 ml/l/month) MOX wines) (4) Control + chips + lees + MOX #Total phenols (in MOX wines) (9 ml/l/month) Bottle storage ", Increase; #, decrease;!, no change; MOX, microoxygenation; MLF, malolactic fermentation; O2, oxygen; a*, red colour component; b*, yellow colour component; AF, alcohol fermentation; CDRSO2, colour owing to pigments resistant to SO2 bleaching; W1,W2,W3, wines from Monastrell grapes of different phenol content; Cl, colour intensity; TCP, total colour of pigments; WC, wine colour; TMA, total monomeric anthocyanins; CAW, chemical age of wine; SO2, Sulfur dioxide; TAC, total antioxidant capacity. 380 wileyonlinelibrary.com/journal/jib Copyright 2013 The J. Inst. Brew. 2012; 118:

14 Microoxygenation application in wine Microoxygenation can also be used to improve the quality of very astringent and herbaceous red wines (101). The majority of compounds responsible for the astringent sensations in red wine are thought to be due to a hugely complex group of polymeric phenols such as proanthocyanidins (43,124,127). The mean degree of polymerization is a method of charactering polymeric phenols or polymerization. Microoxygenation promotes the polymerization of proanthocyanidins, thus the mean degree of polymerization of microoxygenated wine is significantly higher than that of the control wine (101,103). Acetaldehyde, which can react with the tannins and form bridges between tannin molecules, can create macromolecular structures and precipitate, thus resulting in a decrease in astringency. Nevertheless, in order to avoid the development of excess bitterness, oxygen addition must be controlled (10). Most of the studies have shown that microoxygenated wines vs control wines showed a softening of wine due to lower astringency (6,18,101,110,111,117,118,122); however in some studies no difference in astringency was seen (106,108), and in one study an increase in the astringency score was noted (107). For volatile composition and sensory characteristics of wines, microoxygenation treatments resulted in higher scores for the plum/currant and spicy attributes (107,111,117,118) as well as the appearance of tobacco and nutty notes, which were absent in the non-treated wines (117), as well as an increase in toasting, spices and coffee perceptions (101). Red fruit attributes improved (111,117,118), diminished (107) or stayed constant (17) in MOX wines. They also presented a clearer impact of wood aromas (101), especially combined with chips (122) as the MOX wine was more extracted from wood than the control wine or because microoxygenation before oak aging emphasizes these aromatic notes (101). In wines microoxygenated with oak chips and yeast lees, a vanilla perception has been noted, as well as sensory characteristics perceived in the preferred wine (122). MOX affects wine aroma, but the effect depends to a large extent on the variety (17,90), and also on the vintage effect, for the result of MOX on some volatile compounds (17). In contrast to these results, the microoxygenation effect on colour stability is independent of variety and vintage factors (95). The antioxidant capacity of the MOX wines was also studied (8,100,106) and the effect of microoxygenation on the antioxidant profile of the red wine was variety dependent (8). The controlled addition of oxygen into well-structured wines does not lead to significant changes in the antioxidant profiles. No differences were found between the control and the microoxygenated wines for antioxidant capacity or scavenger activity (8), in contrast to the findings of a few researchers. Despite increased concentrations of gallic acid, especially in high-dose oxygenated wines, a decrease in the total antioxidant capacity of the wine was observed (106). Another study showed that single bioactive phenolic compounds of wine decreased with oxygen addition (100). As stated before, small and controlled oxygen addition can be applied in combination with oak chips in stainless steel tanks. This may show the appearance of an interaction between oxygenation of the wine and compounds extracted from toasted oak (6,113). It was said that anthocyanins are more effectively linked to oligomeric and polymeric procyanidins, in other words they lead to a decrease in monomeric procyanidins and an increase in polymeric phenolics with the chip maceration process and oxygen (117,118). There have been some studies investigating the combination of microoxygenation and oak chips. There was no significant difference between the MOX wines and control wines, but the type of the chip influenced the final concentration of the volatile compounds of the wine. Origin, size and toasting degree of the oak chips are important factors (121). In another study, the effect of origin (American, French, Spanish) and the size of the oak chips or staves on microoxygenation during red wine aging was researched. The origin and size of the wood used affect oxygen management during the process. As a result, wine treated with staves (larger pieces of wood) and also aged with French oak products consumed more oxygen (119). It has been reported that grape variety and especially microoxygenation had more influence on phenolic composition and wine colour than the type of chips used to macerate the wines. In other words, the selection of one chip or another did not modify the chromatic characteristics of the red wines (116). Wines produced using yeast lees, chips and microoxygenation (122,123) also have a more stable colour (123). This treatment slightly affected phenolic composition; however, it increased the red blue polymeric pigments and colour stability more than the other treatments (123). Nevertheless, for sensory characteristics, the preferred wine is that which is produced using lees, chips and microoxygenation, in comparison with wines using only oak chips or wines using oak chips and microoxygenation (122). There are a number of studies that have found that microoxygenation can be applied during different stages of the wine-making process. It can be applied at the end of alcoholic fermentation (106) and prior to malolactic fermentation (8,17,18,90,95,96,105,107,108,110, ,121), after malolactic fermentation (6,22,111,114,115,122,123,128), both before and after malolactic fermentation (2, ), before oak aging (101), during storage (22,109) or during the aging (100,113,120) of the wine. The goals of microoxygenation can be achieved when it is performed after alcoholic fermentation and prior to malolactic fermentation. This would be more effective because of the instability of the monomeric anthocyanins at this stage. After malolactic fermentation and sulphur dioxide addition, reactions are slower and also additive SO 2 can bind with acetaldehyde and quench oxygen (12). During malolactic fermentation, microoxygenation can be stopped, because some strains of the genera Lactobacillus and Oenococcus are able to metabolize acetaldehyde, even the acetaldehyde bound to SO 2 (129). Nowadays, a popular microoxygenation treatment is applied both pre- and post-malolactic fermentation in different measures of oxygen. The results of applying at each MOX stage can be discussed for the purposes of wine quality. Conclusions Oak barrel aging is traditional in wine-making, to produce high quality wines with high colour intensity and stability, low astringency and a softer feel on the palate. The contact between wine and oxygen in the oak barrels influences the wine quality. At present, in a much shorter time and at a fraction of the cost, microoxygenation techniques, which are popular with winemakers worldwide, can reproduce the benefits of barrel-aging such as colour, astringency and aroma. The technique can be combined with the addition of oak chips to gain a wood aroma in the wine. Microoxygenation is the controlled introduction of oxygen into wine. Therefore the dosage and duration of oxygen addition 381 J. Inst. Brew. 2012; 118: Copyright 2013 The wileyonlinelibrary.com/journal/jib