Extraction is a crucial operation in winemaking, particularly for red wines. It affects every aspect of wine, from color intensity to aging potential.
In winemaking, extraction refers to the transfer of compounds contained in grape skins and seeds into the juice or wine. Even with black grapes used for red wine production, carefully peeling the skins and pressing only the pulp yields clear juice. Fermenting this clear juice does not produce a red color. To give wine its red color, it is necessary to extract anthocyanins, the pigments contained in the grape skins.
While extraction is routinely performed in winemaking facilities, condition-setting based on scientific evidence is surprisingly uncommon, and many aspects still rely on individual winemakers' intuition.
This article aims to provide a scientific understanding of extraction in winemaking.
The Necessity of Extraction in Winemaking
Extraction is indispensable in winemaking, and its necessity is most clearly recognized when producing the color in red wines. The practice of fermenting red wine with the skins is largely driven by this need to extract pigments.
However, the significance of extraction in winemaking is not limited to pigments—that is, anthocyanin extraction alone. Pigments attract attention because the degree of extraction is visually apparent. Yet the more fundamental importance lies in the extraction of phenolic compounds.
Anthocyanins, the pigments contained in black grape skins that make red wine truly red wine, are themselves a type of phenolic compound.
The Complexity of Phenolic Compounds
Phenolic compounds encompass many varieties, and their chemical classification is somewhat complex. For example, tannins, a term commonly heard in wine vocabulary, are a type of phenolic compound. Tannins specifically refer to certain compounds classified as polyphenols. Moreover, there are multiple types of tannins, making a precise understanding of phenolic compounds rather challenging.
Despite being such a diverse group of chemical substances, phenolic compounds in wine are considered one of the key components determining wine quality. Additionally, phenolic compounds, especially polyphenols, possess strong antioxidant properties and protect wine from oxidation. Consequently, phenolic compounds also influence a wine's aging potential.
These points demonstrate that extraction is important not only for wine color but for much more.
Is More Phenolic Extraction Always Better?
If phenolic compounds are related to wine quality, one might be inclined to think that higher content in wine is always preferable. To verify whether this thinking is correct, let us consider what happens to a wine with exceptionally high phenolic compound content.
Effects on Color
First, regarding appearance: higher phenolic compound content results in deeper color.
A high amount of anthocyanins means a high amount of pigments. As pigment quantity increases, color naturally intensifies. Blueberry juice and jam provide clear examples of anthocyanin-based coloring. While there are differences due to the types of anthocyanins present and processing methods, blueberries have high anthocyanin content, which produces such intensely colored juice and jam.
Effects on Taste
Next, regarding taste: higher phenolic compound content increases astringency and introduces bitterness.
Some red wines produce a strong astringent sensation when tasted. This astringency comes from tannins, and as tannin content increases, astringency intensifies. An example of extremely high tannin content is astringent persimmons. The tannin content in astringent persimmons far exceeds that in red wine, so wine never becomes that astringent. However, if one could hypothetically increase phenolic compound extraction indefinitely, the wine would approach such intense astringency.
Additionally, research has shown that flavonoids, which include tannins, are also responsible for bitterness. Therefore, as phenolic compound content increases, bitterness may intensify accordingly.
Balance Between Phenolic Content and Quality
Wines high in phenolic compounds are more likely to have deep color and strong antioxidant capacity, making them capable of long-term aging. However, such wines also exhibit strong astringency and bitterness. While balance matters, wines with disproportionately high phenolic compound content alone do not make particularly enjoyable wines. In other words, regarding phenolic compounds in wine, more is not necessarily better.
The Difficulty of Managing Extraction Levels in Winemaking
We have examined what happens if a wine contains too many phenolic compounds. In winemaking terms, this translates to the question of what happens when extracting very large quantities of phenolic compounds. Simultaneously, this is also an unrealistic hypothetical scenario.
In wine production, no matter how much effort one puts into maximizing extraction, it is nearly impossible to extract such quantities of phenolic compounds that the wine becomes too astringent to drink. Managing extraction levels is actually an extremely difficult task.
Extraction Rates That Remain Low Despite Efforts
Fundamentally, extraction is limited by the quantity accumulated in the extraction target—in winemaking, the grapes used as raw material. This accumulated quantity represents the physical upper limit for extracting that substance. Phenolic compound accumulation varies among grape varieties. Some varieties have relatively high content, while others have inherently low accumulation. Cultivation conditions also exert significant influence, and differences in accumulation levels are not uncommon even within the same variety. When using varieties with low initial accumulation, the quantity of phenolic compounds that can be extracted remains limited regardless of winemaking efforts.
Furthermore, an important point is that multiple studies have confirmed the impossibility of extracting the total quantity of phenolic compounds contained in grapes. The extraction rate of phenolic compounds in winemaking does not increase substantially no matter how much conditions are varied.
Extraction Rate Guidelines
The extraction rate during the winemaking period is complexly related to many factors including accumulation in grapes, ethanol concentration, temperature, liquid-to-solid ratio, and pH. Because extraction is a complex system reaction not governed by conditions alone, no absolute average extraction rate has been established to date. Studies have also shown no consistency in results obtained through verification.
For example, while some verification cases report anthocyanin extraction rates of 80%, many cases report levels remaining around 45%. Tannins show roughly similar trends. Considering that research indicates the extraction tendency of basic phenolic compounds does not differ greatly from that of anthocyanins, while remaining within the realm of personal prediction, it seems reasonable to expect extraction rates to predominantly remain around 40-60%.
Four Conditions That Promote Extraction
Extraction in winemaking is understood as a complex system reaction involving multiple factors. Multiple past verification results show no consistency. However, four elements can be identified as particularly influential and important: temperature, contact time, ethanol concentration, and the hardness of skins and seeds.
Understanding the Relationship Between Temperature, Hardness, and Extraction
Generally, studies indicate that higher temperatures tend to increase extraction efficiency. This is why red wine production includes a technique called hot extraction, which involves processing juice at approximately 70°C before fermentation.
Temperature-based processing is also closely related to the hardness of skins and seeds.
For instance, anthocyanins, the pigments, are contained within the cell walls that constitute grape skins. To extract these anthocyanins more efficiently, it is important to either break down or loosen the cellular structure of the skins through some method. Studies show that extraction efficiency tends to increase as this structure becomes softer.
Multiple factors contribute to skin softening, including temperature, enzymes, and ethanol concentration. Among these, temperature is a crucial element that exerts both direct effects and indirect influences such as activating enzyme activity.
Temperature affects extraction not only when raised but also when lowered. A representative example is cryoextraction. Cryoextraction is a winemaking technique that artificially freezes harvested grapes and is performed with increasing extraction rate as one of its explicit objectives. This process increases extraction efficiency by destroying cellular structure and reducing skin hardness, thereby facilitating extraction.
Understanding When and What Is Being Extracted
The term "extraction" can create the impression that everything produces the same effect. In reality, however, extraction must be understood as something more dynamic—as continuous change occurring along a temporal axis.
The phenolic compound category contains numerous different types of compounds. Their respective characteristics also differ remarkably. Among these differences, the most readily apparent is the difference in solubility.
Extraction does not involve removing phenolic compounds from skins and seeds as solid particles. Rather, extraction is a phenomenon that occurs as phenolic compounds present in skins and seeds dissolve into the surrounding liquid.
Among phenolic compounds, some are more soluble in water while others are more soluble in alcohol. In the winemaking process, alcohol has not yet been produced at the initial stage, so the ratio of water to alcohol in the liquid is 100:0. However, as alcoholic fermentation by yeast progresses, alcohol concentration gradually increases.
This means that among phenolic compounds, those more soluble in water dissolve relatively early, while those soluble only in alcohol are not extracted until later stages of fermentation. To control extraction, one must understand at what point and to what degree the compounds one wishes to extract have the property of being extracted.
The Misconception That Longer Maceration Is Always Better
There is a belief that to extract more phenolic compounds from skins and seeds, one should keep skins and seeds in contact with juice or wine for longer periods. Based on this thinking, skins and seeds are kept immersed in juice or wine for several days before fermentation and again for several days after fermentation ends.
There is a winemaking technique called extended maceration. This is a winemaking technology that, even after fermentation concludes, does not immediately press and separate skins from wine but rather continues maceration to attempt extracting more compounds.
Using this technique has been shown to increase the wine content of phenolic compounds such as seed tannins that tend to extract more abundantly in high-ethanol-concentration environments. However, studies simultaneously show that anthocyanin content tends to decrease. According to one report, the reduction amounted to 44-82%.
These reduction amounts exceed the quantities gained through extended maceration in many cases, and many studies suggest that prolonged extraction conversely reduces the total phenolic content in wine. While it depends on the types of phenolic compounds being extracted, the simple assumption that longer extraction periods enable extracting more compounds is clearly mistaken.
The Concept of Equilibrium State That Governs Phenolic Content in Wine
Phenolic compounds not contained in grapes cannot be extracted. Meanwhile, even if grapes have accumulated large quantities of phenolic compounds, the fact that not all of them can be extracted into wine is a crucial point when considering phenolic compound extraction. Phenolic compounds cannot dissolve indefinitely into juice or wine; there exists an upper limit to this quantity.
Simultaneously, phenolic compounds once extracted into juice or wine are not maintained in a stable manner. Phenolic compound content can decrease through factors such as reactions, precipitation, and adsorption, and this content is considered to be constantly changing.
Extraction can only proceed up to the quantity that wine can retain. However, reaching this upper limit once does not mean the process ends. For example, if losses occur during fermentation due to oxidation-induced precipitation, additional extraction supplies the lost amount—a constant balancing act.
The state where supply and loss constantly repeat while maintaining balance between the two is called dynamic equilibrium. The maximum quantity of phenolic compounds that can be extracted into wine is believed to be governed by this equilibrium state. In other words, extraction exceeding this balance is impossible.
The Limits of Over-Extraction
Even if this balance is temporarily disrupted to extract large quantities of phenolic compounds, verification has already confirmed that such conditions can only be maintained for short periods. The retention period for over-extracted compounds ranges from several weeks to several months in short cases, and at most several years. Multiple verification cases report that content gradually decreased over such periods, ultimately settling at levels equivalent to or, in some cases, lower than those achieved through normal extraction.
Conclusion: Simply Increasing Extraction Is Meaningless
When considering extraction in winemaking, attention tends to focus predominantly on how to increase extraction quantity. Unfortunately, favorable results are not often obtained from this perspective alone.
As we have seen, extraction is a chemical phenomenon where considering only the removal aspect leaves the approach incomplete. If the upper limit that can be maintained is governed by equilibrium state, then no matter how much is extracted, what cannot be maintained will ultimately be lost, rendering the effort meaningless. Extraction is an act performed to incorporate more target substances into wine. This means that what is fundamentally important is not the quantity extracted but rather the quantity maintained after extraction.
Optimizing Extraction Through Equilibrium Point Adjustment
So how can we maintain more of what is extracted and consequently improve extraction efficiency? This requires considering how to increase the quantity of phenolic compounds maintained in wine without leading to losses. In other words, it requires considering how to change the conditions that form the equilibrium point.
Currently known factors that alter the equilibrium point include temperature, redox state, ethanol concentration, and polysaccharide content. By adjusting these elements, the equilibrium point position can be shifted to form a new equilibrium state. However, research also indicates that no fixed optimal value exists for the equilibrium point. In other words, there is no absolute correct answer regarding what adjustments should be made.
Under these circumstances, performing more efficient and effective extraction requires a perspective that encompasses not only the extraction period but also the subsequent management period. Creating an extraction design throughout the entire winemaking process and accumulating optimal responses at each point is indispensable.
