Wine Maturation and Aging

Hatice Kalkan Yildinm

Department of Food Engineering, Ege University, 35100 Bornova, Izmir, Turkey

1. Introduction

Many complex reactions take place during aging - special reactions involving phenolic compounds that affect the final sensory quality of the wine. The final taste, flavour, aroma and sensation of wine is determined by the interactions of the chemical components present in the wine (Sytger el a/., 2011). Aging can be examined in two stages:

  • • The first stage is called maturation, which includes the changes that occur during storage of wine between alcohol fermentation and bottling. It lasts from six to 24 months or sometimes may last for years. Maturation is also called ‘oxidative aging’ because it occurs in the presence of oxygen. The maturation process, including the chemical change that occurs in wine, is effected by many factors that affect the quality of wine. These factors include grape variety, fermentation (alcohol fermentation and malo-lactic fermentation) and storage conditions (Jacobson, 2006; Jackson, 2008).
  • • The second stage is the aging phase that begins after the bottling of the wine. The chemical reactions that occur at this stage are much slower. This stage is also called ‘reducing aging’ because it occurs in absence of oxygen in the bottle (Jacobson, 2006; Jackson, 2008).

Changes in wine during the maturation (storage of the wine in a tank or barrel) and aging phase (after bottling), together with determination of the boundary conditions, determine the composition of the final aged wine (Waterhouse, 2016).

2. Reactions Occurring during Maturation and Aging

The main compounds that are affected by aging are phenols. The phenolic compounds found in wine can be divided into two groups - flavonoids and non-flavonoids (Fig. 1).

The group of flavonoids includes anthocyanins, flavan-3 which contains flavonols, flavones, flavanones. The non-flavonoids include hydroxybenzoic acid, hydroxycinnamic acid and their derivatives, stilbenes (Jackson, 2008; Moreno- Arribas and Polo, 2009). Changes of phenolic compounds occurring at the beginning of wine production stages continues until aging. The new compounds formed during aging are usually with different organoleptic characters than their precursor compounds. In order to control the wine quality, the chemical changes and mechanisms that occur dining wine production and aging must be well understood (Fig. 2) (Waterhouse and Ebeler, 1998).

Simultaneous presence of coloured phenolic compounds (anthocyanins) and colourless phenolic compounds (phenolic acids, tannins, flavanols, flavonols and flavanonols) in wine are responsible for the changes that occur during maturation and aging (Brouillard and Dangles, 1994). The amount of coloured pigments increases when the concentration of phenolic compounds decreases during aging in red wine (Dallas et ah, 1995). Change in colour properties of red wines within the first year of storage, reduction of anthocyanins and the formation of new stable pigments are influenced by many factors, such as temperature, pH, alcohol, S02 and oxygen content (Recameles et ah, 2006). Change in wine colour compounds during wine maturation is considered to be the fastest, especially during the first year. During wine maturation, interactions among anthocyanins and other phenolic compounds are followed by polymerisation reactions, which cause the formation of new pigments and colour changes in wine (Mateusand Freitas, 2001). Changes occurring in the wine phenols during aging are realised by the principal mechanisms that may take place. These complex reactions are divided into some groups:

• destruction of anthocyanins

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Wine phenolic compounds (Jackson, 2008; Moreno-Ambas and Polo, 2009)

Figure 1. Wine phenolic compounds (Jackson, 2008; Moreno-Ambas and Polo, 2009)

Factors related with aging

Figure 2. Factors related with aging

  • • reaction of anthocyanins with compounds containing polarised double bonds
  • • Co-pigment formation process of anthocyanins
  • • condensation reactions of anthocyanins with tannins
  • • reactions of tannins with proteins and polysaccharides, carbocation formation of procyanidins
  • • oxidation reactions of procyanidins, polymerisation reactions of procyanidins (Fig. 3). (Ribaereau- Gayon et al., 2006)
  • 2.1. Destructions of Anthocyanins

Main structure of anthocyanin is given in Fig. 4.

Anthocyanins, responsible for the colour of wine, are major in the changes that occur in the chemical structure of wine (Somers and Pocock, 1990). During maturation and aging, formation of new compounds takes place through oxidation, polymerisation and reduction reactions of anthocyanins, causing changes in the colour of the wine (de Freitas et al., 2017). It is thought that 25 per cent of anthocyanins react with other flavonoid compounds during fermentation and this ratio can reach 40 per cent at the end of one year of aging. It has been reported that the amount of anthocyanin present in the monomeric form decreases in polymerisation reactions and the wine colour is retained in the polymeric pigments. However, the

Changes in phenolic compounds during wine aging (Source

Figure 3. Changes in phenolic compounds during wine aging (Source: Bruce et ah, 1995)

Structure of anthocyanins (Han and Xu, 2015)

Figure 4. Structure of anthocyanins (Han and Xu, 2015)

colour density decreases over time due to the slow precipitation of the polymeric compounds and the drop in monomeric anthocyanins. In addition, the amount of со-pigmented anthocyanin decreases with time during aging (He et ah, 2012). Another reason for the destruction of anthocyanins with aging is connected to the structure of the coloured anthocyanins and tannin. The amount of tannins added to the coloured anthocyanins of aged wines is higher than that of young wines (McRae and Kennedy, 2011). Anthocyanins foimd in the grapes are in an aggregated form. During maturation, the clustered anthocyanins and free anthocyanin molecules may lose sugar and acyl groups. Such reactions are more susceptible to wine oxidation and browning reactions in the wine. These cases can be overcome by polymerisation reactions occurring among free anthocyanins and condensed tannins, proanthocyanidins and catechins. This will minimise the losses. As a result of the increase of the solubility by the polymerisation reactions, the losses due to the collapse are minimised (Jackson, 2016). Polymeric anthocyanins, which are formed as a result of various reactions, are more stable against oxidation and pH changes than monomeric anthocyanins (Fig. 5).

Reactions of anthocyanins in aqueous solutions and wine (Rl, R2 = H, OH, OCH)

Figure 5. Reactions of anthocyanins in aqueous solutions and wine (Rl, R2 = H, OH, OCH}): proton transfer (a); hydration (b); and sulphite bleaching (c) (Source: Cheynier et at., 2006)

Anthocyanins may act as nucleophiles and condense together with carbocations to form more polymeric pigments. The nucleophilic C6 or C8 position of the А-ring of flavanols performs an electrophilic substitution reaction with acetaldehyde, resulting in colourless condensed products. However, when the anthocyanins are added to this reaction, red or purple colour is observed. Consequently, as a result of chemical reactions in the anthocyanins during wine ripening and aging, various coloured or colourless pigments are formed (He et ah, 2008).

2.2. Reactions of Tannins with Proteins and Polysaccharides

Tannin, found in wines (Fig. 6), leads to astringency character of wines. Tannins form stable structures with proteins and polysaccharides. Tannins can combine with these components, depending on the electrical charge of the environment and ions concentration in the wine. Clarification agents are used to

Structure of tannins (Anonymous, 2017) remove these colloids when they are in excess. As a result, the content of tannin in the wine decreases and taste becomes softer (Markakis, 2012)

Figure 6. Structure of tannins (Anonymous, 2017) remove these colloids when they are in excess. As a result, the content of tannin in the wine decreases and taste becomes softer (Markakis, 2012).

  • • The first stage of these reactions involves formation of planar heterocyclic amide bonds between the electron-rich phenol ring В-ring or galloylol ester of the tannin
  • • The second stage involves cross-linking reactions that occur by self-assocation between protein aggregates and bound tannins
  • • In the third stage, protein aggregates coalesce to form colloidal particles and thus the protein-tannin complex leads to precipitation (McRae and Kennedy, 2011)

The formation of the tannin-protein complex is directly related to various factors, such as pH, temperature, ionic strength, as well as protein type and molecular weight. It is easier to form complexes between proteins with high proline amino acid content and condensed tannins (Hagennan and Butler, 1980; Ribaereau-Gayon et al., 2006). The astringency is caused by the proline content of the secreted salivary proteins by human saliva and their interactions with tannins (Haslam et al., 1988). On the other hand, polysaccharides play the role as protective colloids in wine. They prevent the protein-tannin complex from precipitation, thus the leading to haze (Riou et al., 2002; Cheynier, 2006; Del Barrio- Galan et al., 2012).

2.3. Carbocation Formation of Procyanidins

Procyanidins are a sub-class of flavonoids. They are formed in the flavan units by a bond formed between two carbons (C4, Q/Cg). This bond is an unstable and is broken by acid action. Basically, the reaction leads to formation of carbocation (C4~), the first step in the reaction of the procyanidin B3 dimer with dissociation in acidic medium. After this step, various compounds may arise, depending on the effect of nucleophilic compounds or oxidation. It is known that the carbation is formed by nucleophilic compounds, such as thiols, as a result of the reaction of (+) -catechin 4-a-ethylthioflavan-3-ol. Carbocation can also lead to loss of the proton and electron from cyanide pigment. Thus lead to colour changes in wine (Haslam, 1997; Ribaereau-Gayon, 2006).

2.4. Oxidation Reactions of Procyanidins

The oxidation reactions include enzymatic, non-enzymatic and chemical-auto oxidation reactions occurring in wine. In oxidation reactions are involved primarily phenolic components, such as caftaric acid, catechin, gallic acid, anthocyanin and procyanidin. Metals (Fe2+ and Cu+) can act as catalysts in the oxidation. They react with molecular oxygen, leading to browning of wine; especially in white wines, catechins and procyanidins are the primary compounds causing oxidation. Due to the absence of maceration in the production stages of white wine, catechin and procyanidin compounds are present in small quantities. This is the main reason for the increase in oxidative browning in white wines. In red young wines, instability of these compounds is responsible for their marked differences (Butzke, 2010; Panda, 2011). In a previous study it has been reported that procyanidins are more easily oxidised than other phenolic compounds in must-like models containing more caffeoyl tartaric acid (Cheynier et al., 1998).

2.5. Polymerisation Reactions of Procyanidins

Procyanidins can undergo oxidative and non-oxidative polymerisation reactions. Polymerisation reactions of procyanidins occur at the C4-Cs and C4-C6 interflavan bonds directly as a result of the wine pH values. These reactions among the anthocyanin and the procyanidin molecules may occur, both in the absence and presence of oxygen. The effect of oxygen in the medium oxidises ethanol to acetaldehyde, which increases the polymerisation reactions between the procyanidins and anthocyanins. These reactions affect grossly the taste of wine. Besides, these reactions also protect anthocyanins from oxidation and modifications that could occur with other compounds. Due to the increased solubility at the end of the polymerisation, the amount of precipitated tannin is minimised (Reynolds, 2010; Jackson, 2016).

2.6. Co-pigment Formation Process of Anthocyanins

Co-pigmentation is the result of interactions among the anthocyanins and the colourless compounds. Colourless compounds include flavonoids, such as flavonol and flavone subgroups (Boulton, 2001). Copigmentation causes significant changes in colour intensity (Castaneda-Ovando et ah, 2009). A large amount of pigments that emerge in yoimg wines is obtained as a result of the pigmentation reactions of the pigments and their co-pigmentation co-factors (Neri and Boulton, 1966). This process is affected mainly by temperature and pH. At the pH value is 3.5, maximum co-pigmentation may occur, depending on the anthocyanins in the medium and their co-pigment co-factors (Sikorski, 2006). There is a sensible balance between the free anthocyanins and the co-pigments to result in со-pigmented anthocyanins. This balance is affected by competition between co-factors and reactions, such as oxidisation or hydrolysis of cofactors during aging. Therefore, the equilibrium is constantly changing and rebalanced. Co-pigmetation has an important contribution to wine quality since the со-pigmented anthocyanins give more colour than the free anthocyanins (Boulton, 2001).

2.7. Reactions of Anthocyanins with Compounds Containing Polarised Double Bonds

Anthocyanins react with molecules containing polar double bonds by cycloaddition reactions to their C4/ C5 carbons. They tend to form new stable compounds by reacting with acetaldehyde and pyruvic acid, 4-vinylphenols, vinylflavanols which are known as pyranoanthocyanins (Bordiga, 2016). Basically, this reaction consists of a new cycloaddition of compounds between the flavylium molecule and polarised double bond coupled to the oxygen molecule held by the C4/C5 carbons of the double bonded anthocyanins. These new compounds occur at a very slow rate (Ribaereau-Gayon et al., 2006).

2.8. Condensation Reactions of Anthocyanins with Tannins

Condensation reactions between anthocyanins and other phenolic compounds (procyanidins, catechins) are the most effective reactions causing changes in wine colour. These reactions occur among the C4 carbon of anthocyanin molecule and the C6 or Cs carbon of the monomeric tannins, such as catechin, epicatechin or condense tannins (Du Toit etah,2Ql). In direct condensation reaction, the reaction involves the conversion of anthocyanins to flaven form. The electrophilic substitution between the anthocyanin flavylium form (C4) and flavanols, such as procyanidins (C6/C8), involves the formation of a colourless flaven. Another direct condensation reaction involves the formation of a colourless compound as a result of the reactions between the carbocyclic (C4) which occur after the interflavan bond breaks of procyanidin and the nucleophilic bonds (C6/C8) of anthocyanins (Ribaereau-Gayon et ah, 2006; Gonzalez-Paramas et ah, 2006; Bakker and Clarke, 2011). Direct condensation reactions between anthocyanins and tannins or catechins lead to formation of anthocyanin-tannin or tannin-anthocyanin complexes which cause orange colour of wine (Jackson, 2016). There is an also polymeric structure formed due to acetaldehyde- mediated condensations between anthocyanins and flavanols. If this reaction occurs at acidic medium in presence of the catechin, then wine colour changes from reddish violet to orange (Ribaereau-Gayon et ah, 2006; Gonzalez-Paramas et ah, 2006: Bakker and Clarke, 2011).

3. Effects of Wine Production Stages on Maturation and Aging

Many factors may influence the wine aging composition, such as grape variety, cultural processes, ecological factors and wine production techniques (Martin and Sun, 2013) as given in Fig. 7.

Wine composition varies with the grape variety, grape maturation and wine production techniques. Although the grape variety used in wine production reflects the composition of the wine, it can undergo considerable changes during the fermentation of grapes, production process and aging phase (Cheynier, 2010; Martin and Sun, 2013). The changes in the wine after fermentation can be explained by the fact that the wine is in a chemically dynamic state even during aging (Waterhouse, 2016). Specific changes occur in wine composition, contributing to the organoleptic properties of the wine (Morenoand Peinado,

2012). So, the aging stage can be considered as one of the important steps in wine production (Sun,

The factors affecting wine aging

Figure 7. The factors affecting wine aging

  • 2016). Different techniques used at each stage of wine production may contribute to the formation of high concentrations of pigments and tannins of wine, so that these compounds promise a potential for the complex taste and flavour to form during maturation and aging (Somers and Pocock, 1990).
  • 3.1. The Effect of Grape Varieties

The aging period may vary, depending on the grape variety. Red wine produced from grapes of Cabernet Sauvignon, Shiraz, Tempranillo, Nebbiolo and Pinot noir can continue to retain its aroma after decades of aging for several years. White wines produced from grapes, such as Riesling, Chardonnay, Sauvignon Blanc and Viura have a high aging potential (Jackson, 2008). Some wine types (fresh, fruity whites, blushes, light reds and nouveau red wines) do not require prolonged maturation and aging because their quality peaks in a short time (Dharmadhikari, 2017). During aging, white wine generally loses itsr fruity aroma due to caramelisation and sherry-like odour formation while red wines develop bouquet due to reactions with tannins. This is explained by the fact that phenolic constituents in white wine are lower than that in red wines (Markakis, 2012). Additionally, aging time varies according to the grape varieties. White wines, such as Riesling, Chardonnay, Sauvignon Blanc, Parellada, Semilion and red wines, such as Cabernet Sauvignon, Pinot noir, Syrah, Zinfandel have a long aging period. White wines, such as Trebbiano, Muscadet, Pinot Blanc, Kerner, Aligote and red wines, such as Gamay, Dolcetto, Carignan, Grenache, Grignolino have a short aging period (Jackson, 2008).

3.2. The Effect of Grape Harvest Time

The grape harvesting time is closely related to the grape variety, climate, topography and vineyard management practices which directly affect chemical and sensory properties of the wine (Bindon et al., 2013). The degree of grape ripening, the amount of acid and sugar and phenolic compounds are an important criterion for determining the harvesting date (Perez-Magarino and Gonzalez-San Jose, 2006). There are many studies in the literature that show that grape ripening and harvest date affect the phenolic compounds of wines (Perez-Magarino and Gonzalez-San Jose, 2006; Fang et al., 2008). However, few studies have been found that examine the corr elation between harvesting time and aging. Perez-Magarino et al. investigated the influence of different grapes (Tino fino and Cabernet Sauvignon) and different harvest times (conventional, one week and two weeks later the conventional time) on wine aging. Wines matured in medium-fried American oak barrels for one year and then left to bottle aging for six months. It was found that the loss of free anthocyanin during the aging process was highest in Cabernet Sauvignon wines. However Tino fino (one week after conventional time) and Cabernet Sauvignon (two weeks after conventional time) were reported to have the highest levels of anthocyanin. The results demonstrated that the anthocyanins derived from the reduction of free anthocyanin and flavanols in wines increased and that these new pigments were also present in the two wine varieties made from more ripe grapes. However, in these wines, the differences between one week and two weeks after the conventional time were not statistically significant. As a result, they emphasised that the conventional harvest time will have better properties of wines with one or two week delays (Perez-Magarino and Gonzalez-San Jose, 2004).

3.3. The Effect of Maceration

In the stage of maceration, which is responsible for the wine colour, temperature, used method and time are important factors. At this state, significant changes occur in the phenolic compounds content of must; thus, high amounts of colour pigments and tannins can be formed causing colour stability in the wine (Sims and Bates, 1994; Alvarez et a!., 2006). Cejudo et al. investigated the effects of low toasted American oak chips (1 cm2) added at 3 g/L for four days dining maceration stage on Syrah wines, on phenolic component and colour properties of wine. The results demonstrated that must slightly increased the co-pigmentation reactions, including anthocyanin, flavan-3-ols and hydroxycinnamic acid. Additionally it was reported that this application increased the lightness and hue values of wines by 10 per cent and 70 per cent respectively. At last it was emphasised that the aging ability of wines could be improved by this method (Cejudo et al., 2017). In another study done by Gomez-Plaza et al. the effect of different maceration times (four, five and 10 days) was investigated on phenolic compounds and colour properties on the one-year bottle-aged wine. It was foimd that 10 days of maceration caused high ionised anthocyanin, polymeric compound, chemical age and colour intensity values. On the other hand, four days of maceration caused a higher tint value with lower amounts of phenolic compounds. As a result, they emphasised that the increase in the amount of phenolic compounds extracted from grapes duiing a long maceration period gave the wines a high colour intensity and they retained the characteristics of the wines according to their short maceration times. Additionally, it has also been documented that 10-day maceration gave wine a higher sensory evaluation rank (Gomez-Plaza et al., 2001).

3.4. The Effect of Press Process

Basically at this stage, fruit juice is obtained from crushed and pressed grapes. Usually, this process takes place after the must fermentation of red grapes but is directly produced if it is prepared from white grapes before the alcoholic fermentation (Robinson and Harding, 2015). The fruit juice obtained from grapes consists of 85-90 per cent of free-run juice while the remaining (10-15 per cent) portion is a juice obtained by pressing. This part may, however, depend on the grape variety, grape ripeness, pressing type, pressing time and pressing pressure (Amerine and Joslyn, 1970). The pressed juice includes more tannin, anthocyanin and total phenolic compounds than free-run juice. During winemaking, the producers can perform suitable blending procedures by mixing free-running and pressed juice compounds. Given the potential for low aging of free-run juice and the availability of low quality wines, the pressed juice, that enhances the potential of wine maturation and aging with higher tannin content, can be blended in various batches. Pressed juice ratio is determined according to the aging potential of wine (Ribereau-Gayon et al, 2006).

3.5. The Effect of Fermentation

Alcoholic fermentation is a process by which grape sugars (glucose, fructose), found at about 20-25 per cent, is converted to alcohol (10-15 per cent) and C02 by yeasts. During fermentation, there is a comprehensive change in wine due to the extraction of the grape components by yeast metabolism, the enzymes found in grape and in microorganisms. Changes that occur during fermentation include biochemical reactions, while changes occurring during aging include only chemical reactions (Cheynier et al, 2010; Waterhouse et al, 2016). During fermentation, different yeasts produce different metabolites including aroma compounds, such as ethyl esters, acetate esters, higher alcohols, fatty acids and aldehydes. Therefore, fermentation changes the composition of the wine by different yeast metabolites, but the final wine composition is determined by changes in the aging process (Ferreira et al, 1995; Vilanova and Sieiro, 2006; Recamales et al, 2011). Tomasevic et al. (2017) investigated in Posip the effect of maceration/non-maceration, different yeast strains (indigenous and commercial) and antioxidant additions (higher sulphur dioxide and glutathione) on wine aroma of one-year bottle-aged wine. They foimd that fermentation carried out by different yeasts (commercial and traditional yeast) both in maceration and non-maceration had an effect on the esters and higher alcohols that determine the aroma profile of the wine. In the samples of non-maceration and maceration, 12 months of bottle-aging showed a decrease in some important aroma compounds like terpenes, esters, thiols but the reduction was slower in wines with added sulphur dioxide and glutathione as antioxidants before bottling. (Tomasevic et ah, 2017). Malo-lactic fermentation entailing conversion of malic acid to lactic acid in wine (Waterhouse et ah, 2016) has become a desirable step in the aging of red wine and even white wine, with increase in biological stability of wine and with deacidification that occurs during this fermentation (Boido et ah, 2009). Boido et ah (2009) investigated the effects of different culture strains used in malo-lactic fermentation and bottle-aging on volatile compounds of Tannat wines. The aging period in Taimat wines was affected by malo-lactic fermentation time and the strains used for this fermentation. As a result, decrease in some acetates and ethyl esters had an effect on the fruity aroma of wine (Boido et al., 2009).

3.6. The Effect of Clarification

Occurring after wine maturation or before bottling, clarification of wine is provided by stabilisation, removing of unstable compounds and the haze of wine (de Freitas, 2017). Clarification agents used in this process stabilise besides clarifying wines. This process also affects the flavour of wine usually during fining (Henderson and Rex, 2012). Gelatine and egg are often used in combination to reduce the astringency. Bentonite is usually used for protein removal. Polyvinylpyrrolidone (PVP) used in combination with other agents removes polymerised brown pigments formed in wines (Blady, 1997). Bravo Haro et ah (1991) investigated the effect of different clarification agents (bentonite, gelatine and ovalbumin) on phenolic compounds in an aged red wine. They found that albumin had a greater effect on the phenol fractions, causing reduction in polymer forms. Bentonite significantly reduced the amount of free anthocyanin though it was not as effective as the polymer form. Gelatine was less effective than bentonite in reducing the amount of free anthocyanin (Bravo Haro et ah, 1991). Gomez-Plaza et ah (2000) conducted a study through different vinification techniques, such as maceration temperature (25°C and 10°C) and different fining agents (polyvinylpyrrolidone or bentonite and gelatine), different storage temperatures and time on phenolic compounds and colour parameters of Monastrell wine after bottling. The best colour properties of wine were obtained with low maceration temperature (10°C), the polyvinylpyrrolidone clarification agent used for the clarification and storage temperature of less than 20°C. Additionally, it was determined that the values of colour age and polymeric pigment colour increased during the storage period (zero-12 months) but hydroxyl-cinnamic acid and its esters decreased (Gomez-Plaza et ah, 2000).

3.7. The Effect of Storage Conditions

The storage of wines has an important influence on maturation. Oxidation reactions can occur when wine is placed in porous containers, such as wood and reduction reactions could occur when glass and stainless steel containers are used. These reactions can cause changes in the chemical structure of the wine and these may vary, depending on the type of containers used, the time of duration, wine quality and other storage conditions. The quality of the wine may increase with proper storage (Stevenson, 1997; Recamales et ah, 2006). Storage conditions, such as temperature, humidity, light are factors that have direct influence on wine quality (Robinson and Harding, 2015). Somers and Evans investigated the effects of maturation conditions under nitrogen and oxygen at two different temperatures (3°C and 25°C) on the colour composition of wines produced from Shiraz and Grenache grapes. Results demonstrated that reactions of polymeric pigments occur faster under nitrogen gas at 25°C, while oxygen increases the rate of change of colour composition of wines (Somers and Evans, 1986). A study conducted by Somers and Pocock demonstrated that storage conditions cause pigment degradation and affect the colour characteristics of wines (Somers and Pocock, 1990). Arapitasis et al. studied the influence of storage conditions in cellar (15-17°C) and house (20-27°C) on the phenolic compounds of Sangiovese wine for a period of two years. .The amount of anthocyanin in wine stored in the cellar was higher than that stored in the house (Arapitsas et ah, 2014). The effects of pH, temperature, alcohol content, storage temperature and duration in bottle on colour composition of Portuguese wines was determined.

The results demonstrated that the amount of anthocyanin decreased as storage time and temperature increased, but this loss decreased with increasing S02 content. The amount of coloured molecules that are attached to the polymeric pigment increases at high storage temperatures, but decreases with increasing pH and SO,. Additionally, the anthocyanin concentration during storage was not affected by the pH and the alcohol content (Dallas and Laureano, 1994). Used cork varieties also affect the storage of wines. As an alternative to the natural cork that is still in use today, natural and technical cork, synthetic cork and metal screw cork have emerged. Some studies have emphasised that bottles in the vertical position during storage cause more oxygen input than those stored in the horizontal position (Linsenmeier et ah, 2010; Venturi et ah, 2017). However, the other study did not show any such effect (Lopes et ah, 2006). Reactions in bottled wines are slow, allowing limited contact with air (Boulton et ah, 1996). The rate of wine filling during bottling is also an important factor since the amount of oxygen in the bottle can lead to accelerated aging (Anonymous, 2017).

3.8. The Effect of Storage Time

The storage time affects the phenolic components, colour and sensory properties of wines. The effect of time on phenolic composition and colour parameters of Zalema wine was that the amount of total phenols decreased during the second month but increased during the four to six to eight months. Colour values (L*, a*, b*, croma, hue) fluctuated throughout the storage period. At the end of storage, L *, a *, b *, chroma values had the highest rates (Recamales et ah, 2006). The results further demonstrated that the anthocyanin monomers and total flavonols significantly reduced in three months’ time and continued to decrease throughout the storage period (Marquez et ah, 2014). The chemometric properties of wines treated with oak chips at different toasting degrees were effective during the three months of aging and caused significant differences, whereas the effect of the toasting degrees was not observed in one-and-a- half month-aged wines (Dumitriu et ah, 2016).

  • 4. Aging Techniques
  • 4.1. Development in Existing Aging Systems
  • 4.1.1. Barrel System

Barrel system is one of the most used types of aging in the wine industry (Fig. 8). In this system, the wine aroma is enriched through very slow oxidation. The most common type of oak used is Quercusalba from North America, Ouercusrobus and Ouercussessilis from France. The transfer of astringency-

Oak barrels in a winery related phenolic compounds and oak as responsible aromatic compounds to wine are among the benefits of using oak barrels

Figure 8. Oak barrels in a winery related phenolic compounds and oak as responsible aromatic compounds to wine are among the benefits of using oak barrels (Jackson, 2008). The composition and geographical origin of oak are important considerations in selecting the oak for barrelmaking. American oak barrels have high cis /trans-lactone ratios, while French oak barrels have a higher rate of oxygen transfer to barrels (Perez-Prieto et ah, 2003; Fernandez de Simon et ah, 2008; Prida and Channet, 2010; Hemandez-Orte et ah, 2014). At the same time, oak seasoning and toasting degree also affect the composition of the wine. Wines produced in light- toasted oak barrels have less aromatic compounds whereas medium-toasted oak barrels cause enrichment with phenolic compounds. Use of heavy toasted barrels generally leads to production of wines with high volatile phenols (Fernandez de Simon et ah, 2008). The extraction of oak-related compounds is higher in ‘new barrels’ but the preservation effects of individual anthocyanins against oxidation is better in ‘used barrels’ due to release of lower content of ellagitannins, low molecule-weight phenolic, hydrolysable tannins and lower permeability of oxygen. One of the obstacles in use of old barrels (except their expensive care) is that they could be contaminated with Brettanomyces and Dekkera species (Perez- Prieto et ah, 2003: Prida and Channet. 2010).

There are some disadvantages in the existing methods of wine aging. In traditional methods, the use of the barrels is expensive because of the high-space occupation, the blocking of the pore and slow diffusion rate of oxygen. Furthermore, the development of unwanted microorganisms, such as Brettanomyces that affect the sensory properties of wine, may be adversely affected by the frequent use of old barrels (Suarez et ah, 2007; Tao et ah, 2014). Some studies related to barrel system on the chemical and sensory properties of wine are summarised in Table 1.

Table 1. The Effect of Barrel System on the Chemical and Sensory Properties of Wine

Conditions

Types of wine

Effects

References

Barrel

system

New French and new Amerikan oak barrel for 6 months

Red wine

Chemical effects

  • • The total amount of anthocyanin is similar
  • • New American barrel aged wine HC1 index higher than new French barrel aged wine
  • • New French barrel aged wine tannin content higher than new American oak barrel aged wine
  • • Sensory effects (rice wine)
  • • New American oak barrel aged wine woody aroma more than new French oak barrel aged wine.
  • • Astringency and acidity aromas are similar

Perez-Prieto et a/., 2003

New French oak barrel for 6 to 12 months

Red wine

Chemical effects

  • • Furanic compounds increase
  • • Lactones, eugenol, and vanillin content increase
  • • Furfural and 5-methylfurfural content decrease

Sensory effects

  • • Overall oak intensity increase
  • • Fruity intensity decrease
  • • Yanilla/pastry aroma increase

Prida and Channet, 2010

In recent years, new materials such, as Spanish oak (Ouercus robur, Quercus petraea, Ouercus pyrenaica) (Simon et ah, 2003; Simon et ah, 2008), acacia (Robinia pseudoacacia) (Kozlovic et ah,

2010), cherry (Primus avium) (Rosso et ah, 2009), chestnut (Caldeira et ah, 2006; Gambuti et ah, 2010), mulberry (Morusalba) (Rosso et ah, 2009) emerged as an alternative to American and French oaks.

4.1.2. Use of Wood Fragments

Wood fragments are used as an alternative aging system in the form of oak chips and oak staves. Oak chips and oak staves provide quick extraction of wood-related volatile compounds in the first three months of aging, but not later; therefore, it is appropriate only for short-term-aged wines. Wood fragment shapes (oak power, cubes, oak beans, granules and dominos) and geographical origin affect the composition of the wine (Fig. 9).

Some oak fragments

Figure 9. Some oak fragments

The use of wood fragments can reduce the aging time due to high extraction rate for a short time but colour evolution requires a longer time and small amounts of oxygen (Hemandez-Orte et ah, 2014; del Barrio-Galan et ah, 2015). This is a new development as discussed in the subsequent section.

4.1.3. Microoxygenation

Aerobic conditions could grossly influence the wine quality (Somers and Pocock, 1990). Oxygen affects the phenolic compound composition of the wine, leading to changes in sensoiy properties, such as colour and astringency of wine. A small amount of oxygen can improve the sensory properties of red wine (Picariello, 2017). Microoxygenation is an innovative aging method that is mainly applied with low controlled amounts of oxygen in the early stage of wine maturation. The critical point in this method is the amount of oxygen used and the time of application (Blaauw, 2009). This method is different from the passive oxygen uptake that occurs during barrel maturation or barrel aging. Dining microoxygenation, the amount of oxygen used to prevent dissolved oxygen from accumulating should be equal to/or lower than the amount of oxygen in the wine (Gomez-Plaza and Cano-Lopez, 2011).

Microoxygenation can reproduce the benefits of barrel aging in a much shorter time. Microoxygenation application has many benefits, such as incensement of long-term oxidative stability, lowering of S02 requirements in winemaking, provision of more complex wine aroma and additional oxygen for yeast metabolism and decrease of sluggish fermentation (Blaauw, 2009; Gomez-Plaza and Cano-Lopez, 2011). However, in this application there are some risks, such as formation of aldehyde/oxidided aromas and flavour development in wine, incensement of volatile acidity, colour losses caused by the precipitation of phenolics and microbial spoilage (acetic acid bacteria and Brettanomyces) (Perez-Magarino et al., 2009; Gomez-Plaza and Cano-Lopez, 2011). The effects of microoxygenation on the chemical and sensory properties of the wine are summarised in Table 2.

Conditions

Types of wine

Effects

References

Microoxygenation

3 ml L1 month1 for 3 month

Red wine

Chemical effects

  • • Monomeric anthocyanin content decrease
  • • Polymeric peak increase
  • • Higher color intensity
  • • Phenolic and chromatic characteristics very similar to that of a 3 month oak aged wine.

Lopez et al., 2010

Microoxygenation, Oak chips and oak staves

1 mg L1 month1 for 6 month

Red wine

Chemical effects

  • • Color intensity increase
  • • Red color increase
  • • Similar effects to wood barrel
  • • aging (New American and French oak barrels)

Sensory effects

  • • Vanilla and woody aromas similar to American oak barrel (microoxygenation+ oak chips)
  • • Spicy aroma and sweet taste similar to French oak barrel (microoxygenation+ oak staves)

Oberholster et al., 2015

Microoxygenation and oak chips

3 mg L'1 month'1 for 20 days.

Red wine

Oak chips Chemical effects

  • • Highest concentration of alcohol, carbonyl compounds and lactones
  • • Lower concentration (-95%) of flavan-3-ol (respect to microoxygentaion treated ones)

Sensory effects

  • • Floral, fruity, herbaceous character decrease
  • • typical oak aroma become

Microoxygenation Chemical effects

  • • Highest concentration of acids and esters
  • • Highest concentration (+306%) of anthocyanins (respect to oak treated ones)

Sensory effects

  • • Astingency and herbaceous character reduce
  • • Spicy and fhrity aromas increase

Baiano et al., 2016

4.1.4. Aging on Lees

Aging with lees is a process carried out with yeast strains that develop a biofilm on the wine surface after fermentation. The yeast used in the aging process belongs to the genus Saccharomyces and is also called as flor yeast (Alexandre, 2013). The yeasts have the ability to form a biofilm at the liquid- air interface (Alexandre, 2013). The flour yeast consumes the remaining dissolved oxygen, creating a reducing environment. It affects the organoleptic properties of wine and creates special aromas (Moreno and Peinado, 2012). During the aging process with flour yeasts, some metabolites (mannoproteins, carbohydrates) combine with wines compounds (Leroy et al., 1990).

Lees are used during aging of natural sparkling wines, white wines and sherry wine. Aging by using lees could improve the colour stability and modify the aromatic properties of wines. In aging by lees, the state of yeast lees, ethanol content, temperature, acidity, other compounds in wines which can be absorbed on yeast lees are important factors (del Banio-Galanetrt/., 2015; Juega etal., 2015). The effects of lees on the chemical and sensory properties of the wine are shown in Table 3.

Application of non-Saccharomyces wine yeasts, lees aging combined with microoxygenation or wood fragments is the new development in this field.

4.2. New Wine Aging Systems

In recent years, alternative techniques have begun to be tried in wine aging with the idea that aging can be accelerated by new techniques, such as ultrasound, gaimna radiation, electric field, high pressure (Suarez et al., 2007; Tao et al., 2014).

4.2.1. Important Points of Ultrasound

The effect of ultrasound on wine aging process is related to acoustic cavitation, which is concerned with the formation, growth and collapse of microbubbles. The violent collapse of these bubbles produces high temperature and pressure (Martin and Sun, 2013; Zhang et al., 2016; Delgado-Gonzalez et al., 2017). During the use of ultrasound treatment, frequency, exposure time and temperature are important parameters that must be considered. High-frequency ultrasound is not suitable; generally the best results are obtained in the range 20-100 kHz. (Martin and Sun, 2013; Zhang et al., 2016; Delgado-Gonzalez et al, 2017). The effects of ultrasound treatment on the chemical and sensory properties of wine are shown in Table 4.

Application of different ultrasonic treatments by fixed or circulating wines and application of ultrasonic treatment combined with other aging techniques (aging in barrel, aging in bottles) is the new development in this field.

4.2.2. Gamma Irradiation

Gamma radiation is one of the three types of natural radioactivity. The other two types of natural radioactivity are alpha and beta radiation, which are in the form of particles. Gamma radiation is a propagation of radioactive materials, known as electromagnetic quantum waves. Gamma radiation, as one of the types of ionising radiations, has higher photon energy and shorter wavelength than light (Wetherill, 1965; da Silva, 2012). Gamma radiation has emerged as an alternative to chemical preservatives of foods (Gupta et al., 2015). The World Health Organisation (WHO) stated in 1981 that gaimna irradiation technology could be used to increase protection and shelf- life of food products (Naresh et al., 2015). The effects concerning wine are related to accelerating physical maturation. During use of gaimna irradiation, gaimna irradiation dosage (Gy), exposure time, wine type and composition are the important factors (Chang, 2003; Kondapalli et al., 2014).

Wine treated with gaimna irradiation (2400 Gy) had the low'est total anthocyanin content and colour intensity but highest colour age value. It was found that as the storage period increased, the amount of acetaldehyde increased, but after 18 months of storage, there was no significant difference in the amount of acetaldehyde in different doses of wine (Caldwell et al., 1989). The application of gaimna irradiation dose of 600 Gy reduced the pH value in wine. It was found that the colour values of the same dose L value

Conditions

Types of wine

Effects

References

Lees

Saccharomyces cerevisiae 1 for 10, 20, 30, 40, 50 day

White wine

Chemical effects (20 day)

  • • Concentration of most esters and acetates increase
  • • Protein content decrease slightly
  • • Polymeric mannose concentration increase
  • • Lactone content decrease

Sensory effects (20 day)

  • • The best sensorial quality of the wine
  • • More aging than 20 days reduce sensorial quality

Juega et al., 2015

Oak barrel aging + lees for 6 months

Red wine

Chemical effects

  • • Tartaric ester content decrease
  • • Total polyphenol concentration slightly decrease
  • • Flavonol content decrease
  • • Protein concentration decrease

Sensory effects

  • • Woody, astringency, fruity aroma decrease
  • • Acidity increase

Barrio-Galan et al., 2011

Oak barrel aging + lees + microoxygenation (3 mg L'1 month1) for 6 months

Red wine

Chemical effects

  • • Tartaric ester content not change
  • • Total polyphenol concentration slightly decrease
  • • Flavonol content increase
  • • Protein concentration increase

Sensory effects

• Woody, astringency, fruity aroma decrease

Oak barrel aging + oak chips for 6 months

Red wine

Chemical effects

  • • Tartaric ester content decrease
  • • Total polyphenol concentration slightly decrease
  • • Flavonol content increase
  • • Protein concentration increase

Sensory effects

  • • Woody, astringency, fruity aroma decrease
  • • Acidity increase

Conditions

Types of wine

Effects

References

Gamma

irradiation

200. 400, 600, 800 Gy

Rice wine

Chemical effects

  • • Polyol concentration reduction
  • • Ethyl acetate content increase
  • • Acetaldehyde content increase

Sensory effects

  • • No change of wine colour
  • • Fruit fragrance slightly increase as garmna irradiation dosages increase
  • • Fragrance quality increase
  • • Greasy, rice-oil flavour decrease
  • • Astringent increase to some degree as garmna irradiation dosage increase

Chang, 2003

200. 400, 600 and 800 Gy

Maize wine

Chemical effects

  • • Acetaldehyde content increase
  • • Polyol concentration reduction Sensory effects
  • • Fruity fragrance slightly increase
  • • Rosy/flower fragrance dramatically increase
  • • greasy mouth feel decrease

Chang, 2004

Table 5. The Effects of Ultrasound Treatment on the Chemical and Sensory Properties of Wine

Conditions

Types of wine

Effects

References

Ultrasound

20 kHz ultrasound for 1 week.

Rice wine, maize wine

Chemical effects

  • • Alcohol content reduction (rice wine)
  • • Alcohol content increase (maize wine)
  • • Acetaldehyde content decrease
  • • Ethyl acetate content increase (rice wine)
  • • Ethyl acetate content decrease (maize wine)
  • • Polyol concentration reduction

Sensory effects (rice wine)

• Overripe or sherry-like smell decrease

Sensory effects (maize wine)

• Tart, spicy, and unsmooth taste increase

Chang and Chen, 2002

30 kHz ultrasound from 1.8 kPa to 20 kPa for 10 days

Red wine

Chemical effects

  • • Anthocyanin concentration increase
  • • Tannin concentration decrease

Masuzawa et al„ 2000

Table 5. (Contd.)

Conditions

Types of wine

Effects

References

• Lightness (L*) increase; redness (a*) and yellowness (b*) decrease

Sensory effects

  • • HC1 index (index of maturation) decrease at
  • 10 kPa and 20 kPa, increase 1.8 kPa and 5.8 kPa
  • • ЕЮН index( index of smoothness of wine) increase at 1.8 kPa, 5.8 kPa, 20 kPa, decrease at 10 kPa

Greengage wine

Chemical effects

  • • Total acid content increase
  • • Total ester content increase
  • • Alcohol content reduction
  • • Aldehyde and ketone content decrease

Sensory effects

• Improve the sensory quality (highest sensory evaluation score at 45 kHz, 360 W for 30 min)

Zheng el a!., 2014

<100 kHz multiple frequencies for 15 and 30 min.

Red wine, white wine

Chemical effects

• Accelerating chemical reactions

Sensory effects

• Extending the shelf life of wine

Leouhardt and Morabito, 2007

decreased, a* value increased, and b* value increased when compared with the control group (Harder el al., 2013). The effects of gamma radiation on the chemical and sensory properties of wine are shown in Table 5. More work however, needs to be done to understand the effects of gamma irradiation on human health (Chang, 2003).

4.2.3. Electric Field

The application of AC electric field in food and bioengineering has been studied within the last 20 years. AC electric field treatment is also considered as an effective tool to accelerate wine aging. This technology has already been used in some Chinese wine factories. The high voltage electric field not only reduced the content of undesired compounds, such as aldehydes but also increased the contents of free amino acids and esters, which are linked to high-quality wines (Zeng et al., 2008; Lu, 2013; Talele and Benseman, 2013). The effects of electric field treatment on the chemical and sensory properties of wine are summarised in Table 6. Studies on operational parameters should be earned out in future.

4.2.4. Pulsed Electric Field Technology

The pulsed electric field technology is based on the application of short-duration high-intensity electric field strengths that induce electroporation of the cell membranes. The pore formation provokes microbial inactivation and enhances the diffusion of the solutes through cell membranes. This technique is mainly used before fermentation with antimicrobial purpose and din ing maceration-fermentation with the purpose of extraction of phenolic compounds (Puertolas et ah, 2010a, b; El Dan a et ah, 2013). This technique is mainly used before fennentation for the antimicrobial purpose and during maceration-fennentation with the purpose of extraction of phenolic compounds.

Application of pulsed electric field technology combined with other aging techniques (aging in barrel, aging in bottles) could be proposed for future work.

4.2.5. High Pressure

Table 6. The Effects of Electric Field Treatment on the Chemical and Sensory Properties of Wine

Conditions

Types of wine

Effects

References

Electric

field

AC electric field 600 and 900 Y/cm for 3-8 min

Red wine

Chemical effects

  • • Higher alcohols and aldehydes content decrease
  • • Esters and free amino acids content increase

Sensory effect (600 Y/cm for

  • 3 min)
  • • Harsh and pimgent flavor decrease
  • • Harmonious and dainty flavor increase
  • • Fruit aroma decrease slightly

Sensory effect (900 Y/cm for

  • 8 min)
  • • Wine taste becomes binning and undrinkable
  • • Strange and unpleasant aroma increase

Zeng et ah, 2008

Table 7. The Effects of High Pressure Treatment on the Chemical and Sensory Properties of Wine

Conditions

Types of wine

Effects

References

High

pressure

100 MPa for 30 min

Red wine

Chemical effects

  • • Total phenol content increase
  • • Phenolic acid content increase
  • • Flavon-3 ols content reduction Sensory effects (rice wine)
  • • Astringency and bitterness decrease

Sun et ah, 2016

650 MPa for 2 hour

Red wine

Chemical effects

• Color intensity and phenolic compounds decrease

Sensory effects

  • • Sour and fruity odor decrease
  • • Sour, astringent, alcoholic, bitter taste increase
  • • Mouth-feel sensation slightly enhance

Tao et ah, 2012

300-500 Mpa for 2 hour

Fresh claret (bordeaux wine)

Chemical effects

• Boiling point, relative density, redox potential, electrical conductivity, and total acidity change

Sensory effects

  • • Best taste and flavor at 300 Mpa
  • • Pressure higher above 500 MPa would break up claret styles

Lietah, 2005

High pressure provides the activation energy to initiate chemical reactions in wines and consequently, shorten the aging time (Sun et ah, 2016).The application of high pressure during wine aging causes changes in boiling point, relative density, redox potential, electrical conductivity and total acidity of wines. Long-term studies are needed to further realise the full potential of this technique (Chen et ah, 2016; Sun et al., 2016; Zhu et ah, 2016). The effects of high pressure treatment on the chemical and sensory properties of the wine are summarised in Table 7.

5. Conclusions

For production of high quality wines, aging is an important step in winemaking. Current technology in this regard that makes use of oak-barrel aging is an effective and reliable method and should not be completely abandoned. However, use of food fragments provides wood-related phenols and aromas to wines and could be used in combination with other technologies, Further, application of microoxygention and yeast lees improves physicochemical and sensory properties of wines and could also be used in combination with other technologies. Physical methods (ultrasonic waves, gamma rays, electric field, nano-gold photocatalysis, high pressure) provide drastic reduction in aging time but further studies on operational parameters and their effects should be carried out.

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