The Colourful Chemistry of Wine: How Wine Colour is Produced from Vineyard to Glass
Our Dajril-Marri Merlot is brightly hued, despite only have 12 hours of skin contact, because of its low pH.
Introduction
Wine comes in many different colours. We typically describe it as white, red, rose, or amber/orange, yet within each of those well-understood categories exists an artist’s palette of colour. White wine can be described as anything from pale green to golden or straw coloured; red wine colour descriptors range from ruby and garnet through to brown. Rose can range from the palest of pinks through to a bright fuchsia. Skin contact whites also have a wide and varying range. Some look more like a white wine, appearing to have very little colour to them at all, whereas others take on a rich, amber-coloured hue. And everything in between these extremes can be found the world of wine.
The colour of wine is interesting not only because it’s one of the first things that we notice about wine after it’s poured, but also because it can make a wine more or less visually appealing and creates expectation about what we’re going to taste. Our Ambrosia Nat is the perfect example of this - that looks totally unappealing, said no one ever.
For experienced wine drinkers, a wine’s visual appearance, especially it’s colour, can provide a lot of clues about the wine. How it’s been made, where it’s from, what grape variety it might be, and it’s age can all be deduced from colour. In this article, we explore a range of factors that shape the colour of wine and determine what ends up in the glass, starting with grape variety.
Grape Variety
Wine acquires its colour from pigments found in grape skins and, to a lesser extent, from compounds formed during fermentation and aging. Anthocyanin is the main pigment responsible for red wine colour, while flavonoids contribute to the colour of white wines. Different grape varieties have distinct genetic profiles, and these genetic variations influence the presence and quantity of anthocyanins and flavonoids in their skins. Some grape varieties are genetically predisposed to produce higher levels of anthocyanins and flavonoids, resulting in darker and more intensely coloured grapes. The thickness of the grape skins can also vary between different varieties. Thicker skins tend to contain more colour compounds and grapes with thicker skins are capable of producing wines with deeper coloration.
Thick skins and intense skin pigmentation have developed as a form of protection against the microclimate and environmental factors in each different grape variety’s specific historical growing regions. For instance, thick skins act as a natural shield against intense sunlight and harmful UV radiation. Grapes exposed to excessive sunlight can experience sunburn, which damages the grape's outer layers. Thick-skinned grapes are more resistant to sunburn and can withstand prolonged sun exposure without harm. UV radiation can also affect the grape's DNA, so skin pigmentation provides additional protection against UV damage, acting almost like sunblock, preventing harsh UV light from penetrating the flesh and most importantly, the seed.
Thick grape skins also act as a physical barrier against pests and pathogens. Insects, birds, and fungi find it more challenging to penetrate the grape's skin, reducing the risk of damage or infection. This added layer of protection helps maintain grape health and gives it a greater chance of reaching phenolic ripeness and therefore achieving reproductive capacity.
Thick skins serve as an insulating layer that reduces water loss from the grape due to evaporation. In hot and arid climates, grapevines with thicker skins are better equipped to retain moisture and resist dehydration, even during extended periods of drought. The thicker skin can also moderate temperature fluctuations within the grape. This is especially important in regions with extreme temperature variations between day and night. Grapes with thicker skins may experience less extreme temperature changes, which can help maintain biological processes taking place as the grape ripens.
To understand why a specific grape has developed in the way that it has, think about where it’s from. Pinot Noir, from the mild climate of Burgundy has relatively low colour and thin skins, whereas Cabernet Sauvignon, from the warmer and sunnier Bordeaux, has thicker skins and more colour pigmentation.
Colour Development in the Vineyard
As grapes ripen, the pigment concentration in the skins increases, influencing the final colour of the wine they produce. Ensuring that grapes are picked at optimal ripeness is vital, as the pH decreases during ripening until reaching its peak, after which it begins to increase due to enzymatic activity breaking down organic acids, as well as rising sugar levels. I will go into why pH is an important factor in wine colour in more detail below but suffice to say, this careful timing ensures the best flavour, colour, and stability for wineries like us, who don’t use additions to adjust pH.
The same grape variety from a different site, or even grapes from the same site but a different season, can develop colour at different rates, in slightly different hues, and at different intensities. The concentration of anthocyanins and flavonoids in the grape skins is affected by the grape's exposure to ultraviolet (UV) light. Grapes in warmer climates receive more sunlight and heat, which accelerates the ripening process and leads to greater colour accumulation. Warmer climates often produce grapes with deeper colour pigments, resulting in darker wines, whereas in cooler climates, grapes may have lighter colours due to slower ripening. The length of the ripening period, which varies with climate and site, affects the development of colour compounds. Longer, slow ripening can result in more colour accumulation and complex flavours.
Water availability also plays a significant role in colour development in grapes, both rainfall and irrigation. Drought stress, where grapevines receive less water, can result in more concentrated flavours and colours in the grapes. Excessive rainfall during ripening can dilute the colour compounds in the grapes.
Pruning can also play a role in colour development, by changing the microclimate and sun exposure of the vine and specific grape bunches.
Maceration
Once the grapes are picked, the amount of anthocyanin or flavonoid extracted from the grape depends largely on the amount of contact between the skins and the juice. If you think about any normal grape that you might eat, if you were to cut it in half, the flesh would most likely be translucent whilst the skin is green or even gray-ish in the case of white varieties, or red in the case of red varieties. The exception to this is teinturier grapes, which have red skin and red flesh, but they are only a small proportion of all red grapes (less than 2%), so in general, red grapes still have translucent flesh. To get the red colour in wine, the juice and skins remain in contact for an extended period, which could be anything from three days to a year or more. Rose is simply wine made from red grapes with only a small amount of skin contact, anything from a few hours to perhaps a day or so. Orange wine, like red wine, is made from white grapes but, whereas white wine is made by what we call “direct pressing” the grapes, so they don’t have any skin contact, orange wine stays in contact with the skins for a few days or longer. It should also be noted that white wine can also be made from red grapes that are direct pressed, though this is fairly rare, except in the case of Champagne and Methode Traditionelle sparkling wine, which often contain Pinot Noir and/or Pinot Meunier that have been direct pressed.
The amount of time that the grapes spend on the skins will determine the depth of the colour extracted, as will temperature during extraction: the higher the temperature, the more colour will be extracted.
The pH Factor
You might not automatically think of pH as an important factor in determining grape colour but it’s actually important for two reasons. Firstly, because it plays a significant role in determining the acidity or basicity of a solution. This is important because it determines how soluble bonds between the colour compounds and the grape skin or flesh are. More acidic solutions are better able to break these bonds and extract flavonoids and anthocyanins. Wine typically has a pH range of about 2.8 to 4.0, with lower pH values indicating higher acidity levels. Lower pH values favour flavonoid extraction, resulting in fresher and more vibrant colours in white wines. Higher pH levels can cause colour shifts towards deeper amber tones while in red wine, lower pH levels can promote better extraction of anthocyanins, resulting in a deeper and brighter colour in the wine.
The second reason why pH is interesting and important is because it influences the wine’s colour as it ages. More acidic solutions will tend to promote stability over time because the acid basically acts as a preservative, preventing an array of chemical reactions from taking place. Think about pickles and how stable they can be long-term for this reason. In wine, a low pH prevents sulphur dioxide (which is produced naturally by the yeast during fermentation, as well as being added by some winemakers) from binding with anthocyanins, forming colourless complexes. This can reduce the wine's colour intensity.
It should be noted, though, that lower pH is not always better. If the pH is too low compared to other components in the wine, the tannins and/or anthocyanins won’t polymerise, making the wine taste sharp and astringent. In addition, because the compounds haven’t polymerised, it can reduce the wine’s overall ageing potential, because unpolymerized flavour compounds are more prone to oxidation. The key with pH (as with so many other things in wine, and life) is to find the right balance between it and the other elements.
Conclusion
In conclusion, the colour of wine is not just a superficial aspect; it holds valuable information about the wine's origin, grape variety, and even its aging potential. The diverse range of colours within the categories of white, red, rose, and skin contact wines reflects the rich tapestry of the wine world.
Grape variety plays a pivotal role in shaping the colour of wine. Variations in skin thickness, genetic profiles, and adaptation to specific climates result in a spectrum of hues. Thick-skinned varieties, like Cabernet Sauvignon, develop deeper color pigments as protection against UV radiation, pests, and dehydration.
The microclimate, including sunlight exposure, temperature fluctuations, and water availability in the vineyard, also influences colour development. Grapes exposed to more sunlight tend to produce darker wines, while drought stress can lead to more concentrated colours. Pruning and canopy management can further fine-tune grape pigmentation.
Maceration, or the contact between grape skins and juice, affects the depth of color. Longer maceration and higher temperatures result in more color extraction.
The wine's pH level plays a dual role. It influences color extraction during production, with lower pH favoring flavonoids in white wine and anthocyanins in red wine. Additionally, pH affects a wine's aging potential, as low pH prevents color loss due to the binding of sulphur dioxide with anthocyanins. However, an excessively low pH can lead to undesirable effects on taste and aging.
For wine enthusiasts, grasping these factors can enhance appreciation of wines that not only exhibit a striking appearance but also authentically express the grapes and the unique terroir. The colour of wine becomes a source of fascination that commences in the vineyard and unfolds during the winemaking experience. It's not just a feast for the eyes but a tantalizing prelude to the sensorial voyage that lies ahead, promising an enriching tasting experience.
