The theory and practice of winemaking have changed fundamentally since its beginnings some 7500 years ago. Advancements, once sporadic, have come at an ever-quickening pace, reflecting developments in science and technology. Improvements in glass production and the use of cork favored the development of wine styles that benefitted from long aging. Sparkling wine also became possible. The research by Pasteur into problems of the wine industry during the 1860s led to solutions to several wine “diseases.” These studies also laid the foundation of our understanding of the nature of fermentation.
Subsequent work has perfected winemaking skills to their present-day high standards. Further study should result in premium wines showing more consistently the quality characteristics that connoisseurs expect. In addition, distinctive features based on varietal, regional, or stylistic differences should become more discernible and controllable. Dr Richard Peterson, a highly respected winemaker in California, has commented that Mother Nature is “a nasty old lady, who must be controlled.” Modern enologic and viticultural science is increasingly providing the means by which many of the vicissitudes of Mother Nature can be moderated, if not controlled.
Modern wine production makes significant demands on the winemaker’s ability to make the “right” choices among multiple options available at almost every stage from harvest to bottling. In addition, there exist major philosophical differences concerning how and why wine is made. Some producers claim (at least in public) that “wine is made in the vineyard.” The winemaker being only a midwife, permitting the unique attributes of the grapes to manifest themselves.
Others feel that grapes are “putty” in the hands of the producer. Production procedures are selected to mold the wine (within limits) to possess the characteristics desired by the artisan cellar master, or shaped to possess the attributes thought to be desired by the target consumer. These differences are the enologic equivalent of the nature-nurture debate in human development. Superimposed on these viewpoints may be limitations imposed by traditional styles or Appellation Control regulations.
Fundamentally, there are no inherently right or wrong decisions, just choices that are more or less appropriate or required under particular conditions. Because grape characteristics vary from vintage to vintage, no set production formula is possible. What is crucial is that the winemaker be fully aware of the benefits and shortcomings of the techniques available, permitting the selection of the optimal, or most judicious, procedure. In the following chapters, the advantages and disadvantages of alternative procedures are presented to facilitate making rational decisions.
Basic Procedures of Wine Production
Vinif cation formally begins when the grapes, or juice, reach the winery. The basic steps in the production of table wines are outlined in Fig. 7.1.
The first step involves removing the leaves and other extraneous material from the grapes. The fruit is then crushed (or pressed) to release the juice and begin the process of maceration. Maceration facilitates the extraction of nutrients, flavorants, and other constituents from the pulp, skins, and seeds. Initially, hydrolytic enzymes released from ruptured cells promote this liberation.
The cytotoxic action of pectic enzymes further promotes the release of cellular constituents into the must (grape macerate). Enzymes released or activated by cell death may also activate the syntheses of flavor compounds and hydrolyze macromolecules to forms utilizable by yeast and bacteria.
For white wines, maceration is kept to a minimum and seldom lasts more than a few hours. The juice that runs freely from the crushed grapes (free-run) is usually combined with that released by pressing. The free-run and first pressings are usually combined and fermented together. Subsequent pressings are typically fermented separately.
For red wines, maceration is prolonged and occurs simultaneously with alcoholic fermentation. The alcohol generated by yeast action enhances the extraction of anthocyanin and promotes the uptake of tannins from the seeds and skins (pomace). The phenolic compounds solubilized give red wines their basic properties of appearance, taste, and flavor. They are also required to give red wines their aging and mellowing characteristics.
In addition, ethanol augments the liberation of aromatic ingredients from the pulp and skins. After partial or complete fermentation, the free-run is allowed to flow away under gravity. Subsequent pressing extracts press fractions (most of the remaining juice). Press fractions may be incorporated with the free-run in proportions determined by the type and style of wine desired.
Rosé wines are typically made from red grapes exposed to a short prefermentative maceration. The grapes are crushed or gently broken, and the juice left on the pomace at cool temperatures until sufficient color has been extracted (generally between 12 and 24 h). The free-run juice is subsequently drawn off and fermented similarly to that of a white wine. Alternately, the grapes may be pressed whole (a slow process associated with limited color extraction). The free-run juice and some of the first press-run juice are fermented without further contact with the skins. Where the coloration of the grapes is low, the grapes may be crushed and fermented with the skins until sufficient pigment has been extracted.
Subsequent fermentation of the free-run juice occurs without further skin contact. When color depth is used to time pressing, consideration must be taken for both pigmentation loss during fermentation and the bleaching action of any sulfur dioxide added. Because of the short (or incidental) maceration, alcoholic fermentation often begins in earnest only after the juice is separated from the skins.
Fermentation may start spontaneously, due to endemic yeasts derived from the grapes, but more frequently from crushing equipment. Standard practice, however, is to inoculate the juice or must with a yeast strain of known characteristics. Yeasts not only produce the alcohol, but also generate the general bouquet and flavor attributes that typify wines.
After completing alcoholic fermentation, the wine may be treated to foster a second, malolactic fermentation. Malolactic fermentation is particularly valuable in cool climatic regions, where a reduction in acidity ameliorates the wine’s taste characteristics. Although most red wines benefit from malolactic fermentation, fewer white wines profit from its occurrence. The milder fragrance of most white wines makes them more susceptible to potentially undesirable flavor changes induced by malolactic fermentation.
The retention of acidity also adds to their fresh taste. In warm viticultural regions, malolactic fermentation is often unneeded and undesirable. Its development is usually discouraged by practices such as the addition of sulfur dioxide, early clarification, and storage under cool conditions.
Newly fermented wine is protected from, or given only minimal exposure to oxygen during maturation. This limits oxidation and microbial spoilage. During storage, excess carbon dioxide escapes, yeasty odors dissipate, and suspended material precipitates. Changes in aroma and development of an aged bouquet may begin during maturation. Exposure to air is usually restricted to that which occurs during racking, or battonage (during sur lies maturation). Such slow or limited exposure can help oxidize hydrogen sulfide and favor color stability in red wines.
After several weeks or months, the wine is racked. Racking separates the wine from solids that settle out during spontaneous or induced clarification. The sediment consists primarily of yeast and bacterial cells, grape cell remains, and precipitated tannins, proteins and potassium tartrate crystals. If left in contact with wine, they can lead to the production of off-odors, as well as favor microbial spoilage.
Prior to bottling, the wine may be fined to remove traces of dissolved proteins and other material. Otherwise, they could generate haziness, especially on exposure to heat. Fining may also be used to soften the wine’s taste by removing excess tannins. Wines are commonly chilled and filtered to further enhance clarification and stability. At bottling, wines are generally given a small dose of sulfur dioxide to limit oxidation and microbial spoilage (between 0.8 and 1.5 mg/liter free molecular SO2). Sweet wines are usually sterile-filtered as a further protection against microbial spoilage.
Newly bottled wines are normally aged at the winery for several months to years before release. This period permits wines blended shortly before bottling to “harmonize.” In addition, it allows acetaldehyde produced following bottling (as a consequence of incidental oxygen uptake) to be converted to nonaromatic compounds. Thus, the “bottle sickness” induced by acetaldehyde usually dissipates before the wine reaches the consumer.
Prefermentation Practices
Stemming and crushing are typically conducted as soon as possible after harvesting. During the harvest, some grapes are unavoidably broken and their juice released, whereas others may be bruised. Thus, oxidative browning often begins before the grapes reach the winery and crushing begins. The juice also becomes field-inoculated with the yeast and bacterial flora present on grape surfaces. If the berries are harvested during the heat of the day, undesirable microbial contamination can rapidly develop. To minimize this occurrence, grapes may be sulfited after harvest or harvested during the cool parts of the day.
Left in containers, harvested fruit quickly warm due to the endogenous metabolic activity of the grapes and the insulating influence of the volume. This can aggravate contamination by speeding microbial activity. In addition, warming may necessitate cooling to bring the temperature down to an acceptable prefermentation value.
Destemming
The present-day trend is to separate the processes of stemming and crushing physically, if not temporally. The removal of stems, leaves and grape stalks (termed MOG –material other than grapes) before crushing has several advantages. Notably, it minimizes the uptake of phenolics and lipids from vine parts. The extraction of stem phenols is of potential value only when dealing with red grape varieties low in phenol content, such as ‘Pinot noir.’ Stem phenols are intermediate in astringency and bitterness, relative to the less strident tastes of skin tannins and the more assertive seed tannins. The phenolics extracted from stems include catechins, flavonols (notably quercetin), and caftaric acid (Sun et al., 1999).
In the past, stems were often left with the must throughout fermentation, especially in the production of red wines. Occasionally, some of the grape clusters were left uncrushed (Henderson, 1824) – thus, permitting partial carbonic maceration. The presence of stems made pressing easier, presumably by creating drainage channels along which the juice or wine could escape.
Modern improvements in press design have made stem retention unnecessary, unless specifically desired. The enhanced tannin content derived from prolonged stem contact gave wines, made during poor vintage years, extra body and improved color density.
In addition to augmenting phenol extraction and facilitating pressing, maceration with the stems may increase the rate of fermentation. This effect appears to be due to the enhanced uptake of oleanolic acid (Bréchot et al., 1971). It supplements the amount of long-chain unsaturated fatty acids available to yeasts. It especially helps them complete fermentation under cool cellar conditions.
Leaf removal before crushing helps limit the production of C6 (“leaf”) aldehydes and alcohols. They are produced during the enzymatic oxidation of linoleic and linolenic acids extracted from the leaf cuticle. Leaf aldehydes and alcohols can taint wine with a grassy to herbaceous odor. Nonetheless, they may contribute to the typical aroma of some wines in small amounts.
High leaf content in the must may also result in the excessive uptake of quercetin. If the wine is bottled shortly after fermentation, quercetin can lead to the production of a yellowish haze in white wines (Somers and Ziemelis, 1985). When the wines are matured sufficiently, much of the quercetin precipitates before bottling. High flavonol contents can also generate bitterness in white wines.
For convenience and efficiency, the same piece of equipment often performs both stemming and crushing. Stemmers usually contain an outer perforated cylinder that permits the berries to pass through, but limits the passage of stems, stalks, and leaves. Often there is a series of spirally arranged arms, possessing flexible paddle ends, situated on a central shaft.
Shaft rotation draws grape clusters into the stemmer, forces the fruit through the perforations, and expels the stems and leaves out the end. When stemmer-crushers are working optimally, the fruit is separated from the leaves and stems with minimal breakage. Expelling the stems and leaves in as dry a state as possible avoids juice loss and facilitates disposal. Stems and other vine remains may be chopped for subsequent soil incorporation.
Sorting
Although stemmers may effectively remove MOG (stems and leaves), it does not remove smaller material such as trellis clips, staples, snails, or insects. Stemmers also do not remove immature (green), oxidized (brownish), raisined, or other forms of substandard berries. Where their presence is likely to detectably affect the attributes of the wine, their elimination can be critical. This has usually required manual sorting. Due to increasing labor costs, sorting is economically feasible only for premium wines. This situation may change with the development of automatic sorters. These can differentiate and selectively remove undesirable material from harvested grapes (Falconer and Hart, 2005).
Rejection can be selected to function on color and/or size categories. As the fruit passes under the detector, located above the conveyer belt, the color intensity of the grapes in the green, red and infrared parts of the spectrum is recorded. Depending on instructions supplied by the operator, the computer determines whether the sample should be rejected. If so, a jet of air expels the undesired material. The sorter can be simultaneously programed to reject grapes, or MOG, based on size criteria.
Although not inexpensive, the automated machine processes grapes more rapidly and at a lower cost (based on several years of use) than manual sorting. Whether such an investment is merited will depend on the economic return derived from improved wine quality.
Crushing
Crushing typically follows stemming immediately. Some berries are unavoidably broken in the process and the juice released is highly susceptible to oxidative browning and microbial contamination. Crushing the fruit without delay permits fermentation to commence almost immediately (if desired), limits microbial spoilage, and provides better oxidation control.
Crushing is accomplished by any of a number of procedures. Those generally preferred involve pressing the fruit against a perforated wall or passing the fruit through a set of rollers. In the former, the berries are broken open, and the juice, pulp, seeds, and skins pass through openings to be collected and pumped to a retaining tank or vat. In the latter process, berries are crushed between a pair of rollers turning in opposite directions. The rollers usually have spiral ribbing or contain grooves with interconnecting profiles to draw the grapes down and through the rollers.
Spacing between the rollers typically is adjustable to accommodate the variation in berry size found among different cultivars or vintages. It is important to avoid crushing the seeds. Otherwise, contamination with seed oils can eventually lead to the development of rancid odors.
Crushing also can be achieved using centrifugal force. In centrifugal crushers, the fruit is spun against the sides of the crusher. Because they tend to turn the fruit into a pulpy slurry, centrifugal crushers generally are undesirable. Clarification of the juice is difficult, and seeds may be ruptured.
Although grapes are customarily crushed prior to vinification, there are exceptions. The juice for sparkling wine production is typically obtained by pressing whole grape clusters. Special presses extract the juice with a minimum of pigment and tannin extraction. The absence of pigments and tannins is particularly important when white sparkling wines are made from redskinned grapes. Pressing intact grape clusters is now becoming popular with some table wine producers.
Botrytized grapes are also frequently pressed, rather than crushed. The gentler separation of the juice minimizes liberation of fungal dextran (β-glucans) polymers into the juice. The latter can plug filters used in clarification. In the production of the famous botrytized wine Tokaji Eszencia, the juice is derived solely from liquid that drains away freely from heavily infected grapes. No pressure other than the weight of the fruit activates juice release.
In the production of wines employing carbonic maceration, such as vino novello and beaujolais, it is essential that most of the fruit remain uncrushed, at least at the beginning. Only in intact berries can an internal grape fermentation occur. This is essential for development of the characteristic fragrance shown by these wines. After a variable period of autofermentation, berries that have not broken under their own weight are pressed to release their juice. Fermentation is completed by yeast action.
Supraextraction
An alternative to crushing is supraextraction (Defranoux et al., 1989). It involves cooling the grapes to 4 ºC, followed by warming to about 10ºC before pressing. Freezing causes both grape-cell rupture and skin splitting. These facilitate the escape of juice during pressing. Although increasing the extraction of sugars and phenolics, supraextraction reduces total acidity and raises the pH. The latter may result from crystallization and removal of tartaric acid.
Maceration (Skin Contact)
Maceration refers to the release of constituents from the pomace (seeds, skins and pulp) following crushing. The process is facilitated by the liberation and activation of hydrolytic enzymes from crushed cells. However, the shift to light fruity white wines in the 1970s resulted in minimizing skin contact. This trend was encouraged by the widespread adoption of mechanical harvesting.
However, depending on the tendency of the grapes to rupture, some inevitable maceration occurred on way to the winery – its extent depending on the duration separating harvest and crushing/pressing, and the temperature of the grapes. Reduced maceration also diminised the uptake of heat-unstable proteins, decreasing the need for protein stabilization products.
Unfortunately, minimizing or eliminating maceration simultaneously reduces the uptake of varietal flavorants located in the skins, such as S-cysteine conjugates in ‘Sauvignon blanc’ (Peyrot des Gachons et al., 2002). For wines depending on aromatics extracted from the grapes, this became increasingly important with the adoption of gentler pressing, such as provided by pneumatic presses or whole-grape pressing.
To offset this deficiency, use of the first and second press-run fractions increased. This option is often easier to manipulate than maceration, due to the complexities of temperature and duration on extraction, precipitation, and degeneration of compounds during maceration. Nevertheless, the addition of press fractions augments the wine’s phenolic content. Like most choices in winemaking, each decision has its pros and cons. In this instance, a potential increase in varietal flavor vs. a potential deterioration in mouth-feel (Tamborra, 1992). What the winemaker needs to know is the relative importance of flavorants derived from the grapes, relative to the ease and extent of phenolic extraction. These properties are largely cultivar dependent, but also vary with vineyard and vintage conditions.
Although prolonged maceration enhances the phenolic content of a white wine, it does not lead to the same degree of astringency typical of red wine. This anomaly appears to result from the absence of anthocyanins. Anthocyanins, which are themselves tasteless, bind with catechins and flavonoid tannins.
This increases the solubility of tannins, keeping them in suspension (retaining their bitter and astringent properties). In white wines, most of the tannins precipitate during fermentation, limiting their potential to affect the wine’s sensory aspects.
Grape varieties differ considerably in the amount of phenolics released during crushing or extracted during maceration (skin contact). For example, few flavonoids accumulate in the musts of ‘Palomino’ and ‘Sauvignon blanc;’ moderate amounts collect in the musts of ‘Riesling,’ ‘Sémillon,’ and ‘Chardonnay;’ whereas extensive extraction occurs with ‘Muscat Gordo,’ ‘Colombard,’ ‘Trebbiano,’ and ‘Pedro Ximénez’ (Somers and Pocock, 1991). An increased phenolic extraction favors subsequent in-bottle browning. This feature may be partially offset by hyperoxidation of the must.
The major physical factors influencing extraction from the skin and pulp are temperature and duration. Extraction is often linearly related to both factors. For example, cool maceration temperatures and short duration minimize flavonoid uptake, and thereby limit potential bitterness and astringency. Occasionally, the concentration of extracted compounds decreases with prolonged maceration, presumably due to precipitation or degradation. Extraction also varies markedly with the class of compounds involved. Although many non-flavonoids are quickly liberated into the juice, subsequent extraction of flavonoid phenolics occurs more readily than nonflavonoids .
As with phenolic compounds, the concentration of flavorants and nutrients is markedly influenced by maceration. For example, skin contact increases the uptake of monoterpenes (Marais, 1996). The content of amino acids, fatty acids and higher alcohols may rise, whereas total acidity tends to fall (Soufleros and Bertrand, 1988; Guitart et al., 1997). The decline in acidity appears to be caused by the increased release of potassium. The latter induces tartrate salt formation and precipitation.
Other changes result from indirect effects on yeast metabolism. For example, increased amino acid availability has been correlated with a reduction in the production of hydrogen sulfide (Vos and Gray, 1979).
Occasionally, a short exposure (15 min) to high temperatures (70 ºC) greatly increases the release of volatile compounds, such as monoterpenes (Marais, 1987, 1996). Although the concentration of most monoterpenes increases on short-term exposure to high-temperature maceration, not all follow this trend. For example, the concentration of geraniol decreases.
Generally, maceration is conducted at cool temperature. This has not only the advantage of suppressing the growth of potential spoilage organisms, before the onset of active fermentation, but also affects the subsequent synthesis of yeast flavorants during fermentation.
For example, the synthesis of volatile esters may increase with a rise in maceration temperature up to 15 ºC, whereas it decreases at higher temperatures. The synthesis of most alcohols (except methanol) is reduced following maceration at warmer temperatures. Methanol content increases due to the action of grape pectinases, which release methyl groups from pectins.
The sensory influence of maceration can also be influenced by the degree of oxygen exposure. This can come from oxygen absorbed during crushing or via intentional exposure (hyperoxidation). Oxygen promotes the enzymatic oxidation of the primary phenolics in white must (non-flavonoid o-diphenols – notably caftaric acid).
Although their polymerization can cause juice browning, the polymers usually precipitate during fermentation. This leaves the wine less sensitive to subsequent inbottle oxidation, as well as lower in bitterness. Although potentially used from some cultivars, hyperoxidation is probably ill-advised with varieties deriving much of their varietal character from volatile thiols, notably ‘Sauvignon blanc.’ Oxygen can degrade volatile thiols.
Partially to facilitate early phenolic oxidation and removal, the addition of sulfur dioxide at crushing is generally avoided. In addition, sulfur dioxide can undesirably enhance the production of acetaldehyde during fermentation, enhance phenolic extraction, and retard the initiation of malolactic fermentation. Adding sulfur dioxide, at or just after crushing, is now largely limited to situations where a significant proportion of the crop is diseased, or where the interval between harvesting and crushing is protracted. Sulfur dioxide limits the action of polyphenol oxidases, and retards the multiplication of bacteria or other microbes in juice released from broken fruit.
Maceration has been observed to improve juice fermentability (Ollivier et al., 1987) and enhance yeast viability. Part of these effects is due to the release of particulate matter, lipids, and soluble nitrogen compounds into the juice. Particulate matter is well known to increase microbial growth. The solids provide surfaces for yeast and bacterial growth, the adsorption of nutrients, the binding of toxic C10 and C12 carboxylic fatty acids, and the escape of carbon dioxide.
This increases must agitation and, therefore, more uniform nutrient distribution. Skin contact facilitates the extraction of long-chain (C16 and C18) saturated and unsaturated fatty acids, such as palmitic, oleanolic, linolenic, and linoleic acids. The enhanced extraction of long-chain fatty acids also reduces the synthesis of toxic mid-chain (C10 and C12) fatty acids (Guilloux-Benatier et al., 1998). The former lipids are important in permitting yeast cells to synthesize essential steroids and build cell membranes under anaerobic fermentation conditions. In addition, the small amounts of oxygen absorbed during crushing and during other prefermentation cellar activities probably promote the synthesis of sterols by yeast cells.
Extended skin contact also improves (more than doubles) the production of extracellular mannoproteins, formed during alcoholic fermentation. The effects of the increased mannoprotein content, and the reduced concentration of C10 and C12 fatty (carboxylic) acids, combine to facilitate malolactic fermentation by Oenococcus oeni (Guilloux-Benatier et al., 1998).
Minimal maceration at cool temperatures often leads to the production of young, fresh, fruity wines. Longer, warmer maceration typically produces a wine deeper in color and of fuller flavor. The latter may mature more quickly and develop a more complex character than wines produced with minimal skin contact (Ramey et al., 1986). Thus, varietal characteristics (Singleton et al., 1980), fruit quality, equipment availability, and market response all play a role in the decision of a winemaker to use maceration, and to what extent.
A new procedure, called cell-cracking, has been investigated as a complement to, or replacement for, maceration (Bach et al., 1990). Cell-cracking involves forcing the must through narrow gaps separating steel balls positioned in a small bore. It promotes the rapid extractions of flavorants.
ROSÉ WINES
Occasionally, rosé wines are made from juice released by pressing whole red grapes. Nevertheless, the more common practice is to gently crush the grapes. This may or may not be followed by a period of maceration, lasting up to 24 hours. Maceration at
20 ºC tends to retard microbial action. Data from Murat (2005) suggest that the top of this range might be preferable, due to improved extraction of S-3-hexan-1-ol-L-cysteine.
This is an important fragrance precursor primarily located in the skin. Its metabolic conversion to the fruity smelling 3-mercaptohexan-1-ol is also favored during fermentation at about 20 ºC. Short maceration also limits anthocyanin uptake, donating only the desired, slight pinkish coloration. However, because few tannins are extracted, rosé wines tend to show poor color stability (much of the color being derived from free anthocyanins, or their self-association or copigment complexes).
Despite their relatively low concentrations, anthocyanins still appear to act as important antioxidants. For example, they protect 3-mercaptohexan-1-ol from oxidation (and rapid loss of this essential ingredient in the fruity fragrance of some rosé wines). Phenethyl acetate and isoamyl acetate are also significant contributors to the fruity flavor to many rosé wines (Murat, 2005).
It is important that maceration occur under anaerobic conditions. This not only limits oxidation of important volatile thiols, but equally protects anthocyanins from oxidative discoloration. Salinas et al. (2003) have found that adding pectolytic enzymes during maceration not only improves flavor development, but also promotes color stability. Both are features important to the shelf-life of rosé wines.
Typically, only free-run juice is used in rosé production. The press-run juice may be added to fermenting red wine or used in other wine products. Unless the grapes were comparatively immature (before full coloration), the anthocyanin content of the press-run is often too high for use in rosé production. Anthocyanin contents in the range of 20–50 mg/liter are standard for rosé wines.
In addition, tannins in the press-run juice can give a bitterness undesirable in most rosés.
Occasionally, in the production of a red wine, a portion of the juice is drawn to produce a rosé. The remaining, concentrated must is used to produce the red wine. The technique, called saignée, is primarily used in years, or with cultivars, where color extraction is likely to be less than desired for production of a red wine.
RED WINES
In red wine production, maceration studies have focused primarily on the extraction of pigments and tannins. Anthocyanins are the first to be extracted, their being more soluble than tannins. As fermentation becomes active, ethanol production not only enhances solubilization, but also facilitates anthocyanin escape by increasing membrane porosity. Tannin extraction is much more dependent on increasing ethanol content for its solubilization.
Both the style and consumer acceptance of wine can be dramatically altered by the duration and conditions of maceration. Thus, maceration provides one of the principal means by which winemakers can adjust the character of their wines. Short macerations commonly produce a rosé. For early consumption, red musts are commonly pressed after 3–5 days. This provides good coloration, but avoids extraction of harsh seed tannins, but extracts sufficient skin tannins to promote color stability. Most flavonoids reach a temporary peak in solubilization within approximately 5 days.
However, there may be a second phase of extraction that begins after 15 days (Soleas et al., 1998). Longer maceration periods are correlated with increased concentrations of higher-molecular-weight tannins. It may also increase the extraction of undesirable flavorants, such as methoxypyrazines (Kotseridis et al., 1999). Wines for long aging have often been macerated on the seeds and skins for as long as 3 weeks. Extended maceration results in a decline in free anthocyanin content, but enhances color stability by encouraging their early polymerization with procyanidins. However, whether the prolonged skin contact, traditional in some parts of France and Italy, is required for wines to age well is a moot point. Little agreement exists among winemakers or enologists.
Although the general correlation between maceration, pumping-over, and style of wine is well known, the ease with which anthocyanins are extracted varies with the cultivar. Romero-Cascales et al. (2005) promote the idea of determining extractability and seed maturity indices to facilitate determining the timing (and method) of maceration. Their extractability index involves measuring anthocyanin uptake at two pH values – 3.6 and 1. Assessment of the seed maturity index is equally important, as it markedly affects color stability. It was obtained using a method described by Saint-Criq et al. (1998).
An old technique undergoing renewed interest, notably with ‘Pinot noir,’ is cold maceration. It involves a prefermentation maceration period (3–4 days) at cool (15 ºC) to cold (4 ºC) temperatures. This is somewhat equivalent to the cooling that usually occurs in small, unheated, Burgundian wine cellars in the fall. This cooling can be more effectively controlled by the judicious addition of dry ice or liquid nitrogen.
The procedure has been reported to slow but facilitate the progressive extraction of phenolics, especially anthocyanins (Cuénat et al., 1996; Feuillat, 1996). Color density is enhanced, whereas flavor development becomes more complex and intense. Heatherbell et al. (1996) reported that cool maceration temperatures generated ‘Pinot noir’ wines with more of a peppery or bitter aspect, whereas cold temperatures tend to accentuate a sweet, blackberry aspect.
Differential flavor effects have also been noted using ‘Airen’ and ‘Macabeo’ cultivars (Peinado et al., 2004). Beneficial effects have also been reported for cultivars such as ‘Pinotage,’ ‘Sangiovese’ and ‘Syrah.’ However, the improved color shown early in maturation is often short-lived, with color intensity becoming similar to traditional treatments on aging (Heatherbell et al., 1996).
A potential disadvantage of cold maceration is an increased risk of early spoilage by Brettanomyces (Renouf et al., 2006). It provides time for adaptation of the indigenous grape flora, and their subsequent growth, when the must is warmed and fermentation begins. The addition of sulfur dioxide promotes anthocyanin extraction, especially at cooler temperatures. Sulfite addition products are more soluble in aqueous alcohol solutions than native anthocyanins. The potential disadvantage of sulfur dioxide addition is that it may delay early polymerization between anthocyanins and tannins.
Another technique for improving color and/or flavor extraction is the addition of supplementary skins, or seeds and skins, to red must during fermentation (Revilla et al., 1998). The procedure is partially based on an old Spanish technique called double pasta. It involves the addition of extra pomace during fermentation.
Enriching the must with grape skins or seeds may enhance the varietal aroma and flavor of the wine. The process also promotes color stabilization. To avoid producing an excessively tannic wine, due to the increased uptake of catechins and dimeric procyanidins, supplementation may be limited to approximately one-third that of the pomace in the original grape must.
Except for cold maceration, little attention has been given to the extraction of aromatic compounds during skin contact. In one of the few studies on the subject, the berry aspect of ‘Cabernet Sauvignon’ was increased by long maceration, whereas the less desirable canned bean–asparagus aspect was diminished (Schmidt and Noble, 1983).
By Ronald S. Jackson in "Wine Science - Principles and Applications", Third edition, Academic Press (an imprint of Elsevier), USA, 2008, excerpts pp.332-340. Digitized, adapted and illustrated to be posted.
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