Why Are Red Wines Red?

Why are red wines red? Many people have probably wondered about this question at some point.

When researching this question, you can generally find the following information:

• The cause of red wine's color is a substance called anthocyanins
• To extract more anthocyanins, the red wine production process involves macerating the grape skins together with the juice

This information is correct. Red wines are indeed red because they contain anthocyanins. It is also 100% true that maceration—the winemaking technique of soaking grape skins together with the juice—assists in extracting these anthocyanins.

However, whether this constitutes a complete understanding is somewhat insufficient.

For example, can this information alone answer the following questions?

• If red wines contain the same anthocyanins, why are there color differences between different red wines?
• What exactly are anthocyanins?
• Is the color of red wine always constant?

To answer these questions, we need to understand "phenols"—the broad category to which anthocyanins belong. Additionally, understanding whether red wine color is stable is essential knowledge for anyone involved in winemaking.

This article provides a thorough explanation of phenols, with a focus on anthocyanins. By reading this article, you should be able to clearly answer questions about why red wine is red and what the key points are for maintaining that color.

It should be noted that this "thorough explanation series" uses some specialized knowledge, including chemical symbols, to understand deeper content. While the articles are written so that you can gain a reasonable understanding by skimming through them, those who want complete understanding are encouraged to research the surrounding knowledge themselves.

What Are Phenols?

The word "phenol" is frequently heard and used when dealing with wine. Readers of this article have probably used this term several times, but do you understand what "phenols" actually are?

Wikipedia explains phenols as follows:

Phenol (phenol, benzenol) is an organic compound with a distinctive medicinal odor resembling watercolor paints. It is one of the aromatic compounds, appearing as white crystals at room temperature. It has a structure where one hydrogen atom of benzene is substituted with a hydroxyl group. The name derives from the old name for benzene, "phene." The Japanese name is coal acid (sekitansan). In the broad sense, it refers to all compounds where hydrogen atoms of aromatic rings are substituted with hydroxyl groups. (Source: Wikipedia, the Free Encyclopedia)

As stated above, phenols in the broad sense refer to "all compounds where hydrogen atoms of aromatic rings are substituted with hydroxyl groups." Therefore, the substances included in this category are extremely diverse. In other words, the first thing to understand is that "phenol" is not a name referring to any fixed substance, but rather a general term for organic compounds with a specific structure.

This point is extremely important when discussing phenols in the context of wine.

Classification of Phenols in Wine

In the context of wine, phenols are classified as follows:

• Phenolic acids
• Flavonoids
• Stilbenes

Furthermore, as subcategories of flavonoids:

• Flavan-3,4-diols
• Flavan-3-ols (Catechins)
• Flavonols

Additionally, belonging to flavan-3,4-diols:

• Anthocyanidins
• Anthocyanins

Incidentally, "tannins"—a substance often mentioned in relation to red wines—is also a general term for multiple substances with certain binding structures. In wine, these are mainly condensed tannins, where catechins (flavan-3-ols) included in flavonoids play a central role.

Tannins also involve flavan-3,4-diols, and the molecular weight of tannins varies depending on their degree of condensation. These differences in molecular weight significantly affect the impression of tannins felt in wine.

Reference

The amount of tannins contained in grape berries is the same whether they are red wine grape varieties or white wine grape varieties. The difference in tannin content between the two types of wines is solely due to how much is extracted.

Phenols Affecting Color Are Not Limited to Anthocyanins

Among the various phenolic compounds classified above, stilbenes are actually the only substances that do not affect wine color. All others influence wine color in some way.

While flavonoids containing anthocyanins have the dominant effect on wine color, it's important to know that phenolic acids also partially influence color.

Phenolic Acids That Color Through Oxidation

Phenolic acids themselves are molecules with short-chain structures that have no color. However, these substances turn yellow through oxidation. In other words, through wine aging, bonding with oxygen progresses, resulting in a yellowish tint being imparted to the wine's color.

The color of so-called aged wines is partially due to this coloration from phenolic acids.

Important Substances Come from Grape Skins

The substances that are decisively important for wine color are flavonols and anthocyanins.

Anthocyanins are, needless to say, the elements that determine red wine color. However, flavonols are the elements that determine white wine color.

Incidentally, both of these are substances contained almost entirely in grape skins, with very little contained in the seeds. In other words, as far as intensifying wine color (increasing anthocyanin extraction) is concerned, soaking grape seeds in the juice during maceration or fermentation has no meaning.

Flavonols, like phenolic acids, turn yellow through oxidation or polymerization. The strongly yellow colors of aged wines and the colors seen in orange wines are based on these substances.

Anthocyanin Colors Are Not Just Red

Anthocyanins are compounds where sugars and organic acids are bound to anthocyanidins.

These anthocyanidins, which can be considered part of anthocyanins, are divided into six types based on differences in terminal group bonding numbers. Among these, the five types of anthocyanidins that affect grape color are:

• Cyanidin: Orange
• Peonidin: Red
• Delphinidin: Purple
• Petunidin: Purple
• Malvidin: Purple

As you can see from the above, even when we speak generally of anthocyanins and anthocyanidins, multiple types of substances are included, and the colors are not uniformly red.

The proportions of these multiple types of anthocyanins basically differ according to grape variety. For example, in the Pinot Noir group (German name Spätburgunder), the proportion of malvidin is higher than other anthocyanidins.

These differences in the proportions of various anthocyanidins lead to the different wine colors that vary by grape variety.

Since anthocyanins are water-soluble, extraction from grape skins can be achieved by macerating skins in the juice. However, raising the liquid temperature can accelerate this process. This is why red wine production processes include steps to raise liquid temperature while the grape berries are crushed, or fermentation with maceration to allow fermentation heat to take effect.

Factors Affecting Anthocyanin Color

Anthocyanin color is not stable and is actually influenced by multiple factors. Understanding these factors that affect color is very important when producing red wines.

The factors that influence anthocyanin color are:

• pH values
• SO2 (sulfur dioxide, sulfurous acid)
• Binding state
• Tannins

Let's examine each of these.

Color Changes Due to pH

Anthocyanins change color depending on the pH of the medium in which they're contained. This occurs because pH changes alter the structure of anthocyanins themselves, and these structural changes modify the characteristics of light wavelength absorption and reflection.

Broadly speaking in the wine field, when pH is below 3, the color becomes red, and when it exceeds 4, the color disappears.

What must be noted here is malolactic fermentation, or lactic acid fermentation.

In malolactic fermentation, lactic acid bacteria convert malic acid to lactic acid. This process raises the wine's pH, so when anthocyanins remain in an unstable state, the wine's color moves in the direction of becoming lighter.

SO2 Lightens Wine Color

SO2—the substance called sulfur dioxide or sulfurous acid—is a factor that lightens red wine color.

SO2 reacts with anthocyanins to generate compounds with no color. Monomeric anthocyanins in particular are sensitive to SO2 and have properties that make them react easily.

One example of color lightening due to SO2 can be seen in ice wines and TBA (Trockenbeerenauslese) dessert wines made from red wine grape varieties.

Dessert wines invariably contain very high levels of residual sugar. Therefore, more SO2 is added than in dry wines to prevent wine re-fermentation and microbial proliferation. Cases where color has been lightened by this large amount of added SO2 can be observed in these wines.

Effects of Binding State on Color

As mentioned in the SO2 effects section above, monomeric anthocyanins are susceptible to various factors and are in a state where their quantity can easily be reduced.

Factors that affect them include the SO2 and pH values mentioned above, as well as aging and oxidation, lees and yeast during fermentation processes, and filters during production processes. Being affected by these factors reduces anthocyanin content, causing color to become lighter.

Note that the maximum value of anthocyanin content depends on grape variety and ripeness.

Color Stabilization Through Bond Formation

Monomeric anthocyanins, left as they are, tend only to decrease in quantity and consequently lose color. However, by bonding with certain substances, they become less susceptible to these surrounding factors and can stabilize color.

A prime example is bonding with tannins and acetaldehyde.

Anthocyanin-tannin-acetaldehyde bonding is achieved under slightly oxidative conditions. To promote this bonding, red wines need to tolerate being placed in oxidative conditions within a certain range.

Related

A secondary effect of this bond formation is that the binding of anthocyanins and tannins reduces wine astringency and bitterness.

From the perspective of this bonding, we can also see that careful handling of SO2 is necessary. SO2 addition creates reductive conditions, plus acetaldehyde bonds very strongly with SO2.

Including the relationship with monomeric anthocyanins mentioned above, you can understand that SO2 can be a factor that lightens red wine color from three different points.

Reference

For SO2 addition, please also refer to the article "Quality Control Basics | How to Use Sulfur Dioxide."

Besides anthocyanin-tannin-acetaldehyde bonding, anthocyanin-anthocyanin bonding and polymerized anthocyanins also affect color stabilization.

The former bonding is mainly generated when heated and doesn't exist much in red wines that have undergone normal fermentation processes.

In contrast, polymerized and long-chain anthocyanins are generated through wine aging. This bonding promotes wine browning. Proteins contained in wine also affect this bonding.

Related

Anthocyanins that have polymerized and increased in molecular weight precipitate as sediment, causing color to lighten. However, adding SO2 can also re-shorten long-chain molecules and restore color as a handling technique.

Aged Red Wine Color Is Affected by Multiple Factors

We sometimes describe the color of aged red wines simply as the effects of oxidation. However, in reality, it's a color resulting from the complex interactions of the truly diverse factors we've examined.

Even from a simple overview, the factors affecting this include:

• Anthocyanins
• Multiple phenolic compounds including flavonols
• Acetaldehyde
• Oxygen

Summary | Why Are Red Wines Red?

Red wines are red because they indeed contain anthocyanins in the liquid.

However, when we speak of anthocyanins, there are many types. These multiple types of anthocyanins, plus multiple types of phenolic compounds and their varying quantities, interact with each other to create each wine's particular "red."

Also, while wine made by simply crushing grape berries, macerating the skins, and fermenting will indeed be red at that point, without proper subsequent treatment, that color cannot be properly maintained.

This includes tannin extraction and external addition for color stabilization, strategic SO2 addition, pH and liquid temperature adjustment, and oxygen control.

The "red" of red wine is not a simple "red" like "because anthocyanins are red," but a "red" where diverse colors are mixed together.