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Bodies of water and their effect on viticulture

Where beautiful wine is produced it is often remarked that one will also find beautiful places. Rivers, lakes, oceans and seas feature almost synonymously amongst many of the worlds best wine regions. The river Moselle, the Saône, the Rhône, the Douro, the Gironde, Margaret River, the Loire, Lake Garda and the North Pacific to name a few. These bodies of water are located at the very heart of the worlds most illustrious wine regions. However, they offer much more to our favourite wines than just a picturesque backdrop, they play a fundamental, and oft-overlooked role.

Balance; the holy grail. This is what we look for, right? There are a few fundamental components to consider when evaluating wine, namely sugar, acid, alcohol and tannin. These components are the legs on the tasting table, when one component protrudes, or stands out, we do not experience balance, the wine wobbles. But how is balance achieved? Time for a quick science recap with a focus placed on acidity and sugar.

It could be said that ripening, if defined as the development of wine grapes, occurs throughout the annual growth cycle of the grapevine. However it is more commonly accepted that fundamentally, ripening occurs at the inception of veraison (around 40 days after fruit-set) At a point prior to veraison, grapes are hard and green with low levels of sugar and extremely high levels of acid (primarily malic) As veraison progresses (usually over 30-70 days dependant on climate) the grapes experience several important changes which alter their sugar, acid, tannin and mineral composition. For the purpose of this article we will focus on the changes made to sugar and acid during veraison.

So, what exactly happens during this period? Concentration of sugar increases and concentration of acid decreases. The increase of sugar is as a result of the storage of carbohydrates in the roots and trunk of the grapevines as well as through the process of photosynthesis. Sucrose produced by photosynthesis is transferred from the leaves to the berries as it is broken down into glucose and fructose molecules. The reduction in acidity is due, in part, to simple dilution but also to the consumption of acids in the process of plant respiration. 

The extent to which climate is able to influence ripening, and in turn balance, cannot be understated. This impact is evident in the vast vintage variation between wines from the same region, appellation, vineyard and producer. Geography, in the case of this article, bodies of water, is able to not only influence but also negate and accentuate the impact and nature of climate.

In many cases bodies of water are a fundamental influencing factor in a particular wines ability to, more consistently than would be considered ‘average’, achieve great balance (in the case of bodies water I refer particularly to sugar and acid balance) Taken to it’s extreme, in the absence of these bodies of water, many wine regions would be devoid of the ability to produce any palatable wine at all. So how exactly do bodies of water influence viticulture?

Have you ever stepped outside on a cold morning to find the ground beneath you frozen solid? Even so, the water in a nearby large body of water remains in its liquid state. How can soil freeze whilst a body of water remains in the liquid state? Water is a polar molecule, this means that it has a slight positive charge on one end and a slight negative charge on the other end. Like tiny magnets, the negative end of one water molecule is attracted to the positive end of another. These attractive forces between water molecules are called hydrogen bonds.

The ability of a substance to hold heat without becoming very warm itself is referred to as heat capacity. Heat energy is measured in calories. Heat energy of 1 calorie is required to raise the temperature of 1g of water 1°C. In comparison, only one-eighth as much energy is needed to raise the temperature of 1g of iron by the same amount. Water has an unusually high heat capacity due to the presence of hydrogen bonds between adjacent water molecules.

For most substances, heat directly affects molecules, causing them to vibrate faster and move apart. Water reacts differently to heat. When water is heated, the initial input of energy breaks apart the aforementioned hydrogen bonds between water molecules. During this period, water maintains its temperature. After all the hydrogen bonds are broken, individual water molecules begin to vibrate and separate, and the temperature slowly increases.

Therefore, it takes more heat to raise the temperature of 1g of water than it does for any other substance. The reverse is also true; as water cools, the water molecules first form hydrogen bonds with each other, maintaining their temperature as they do so. Eventually, cooling slows the motion of the water molecules and the temperature of a water sample drops. The presence of hydrogen bonds causes water to heat slower, and cool slower, than other substances.

The ability of water to hold heat affects climate. Because water holds heat better than soil, ocean temperatures show little variation at night, remaining relatively warm. On nearby land masses, temperatures may drop significantly. When ocean-warmed air rises at night, cool air from the land flows in to replace it, causing wind to blow offshore. This ‘hot water bottle’ effect helps to make the Mosel Valley in Germany one of the country’s warmest regions. It also allows, through moderation of harsh diurnal variation, Riesling (a naturally high acid grape) to ripen effectively in what is considered a cold, temperate climate.

Conversely, during the day, the land warms up faster than the ocean, this reverses the situation. In the evening warm air over land rises and cooler ocean air flows in to replace it (for this reason it is noted that onshore winds blow during the day) Water’s unique heat-retention properties mean that opposed to the Mosel, which is considered ‘cold’, where a region is considered warm (such as the river valleys of Central Spain) the slow warming of the water throughout the day encourages a healthy diurnal shift. This shift ‘reigns’ in the ripening of the grapes, allowing them to retain a balanced level of acids. Oceans and Seas have a particularly profound cooling effect on nearby wine regions. The currents (as mentioned above) fogs and coastal zephyrs they produce mitigate daytime heat in the vineyards. A few wine regions which benefit from coastal influence include South Africa’s Western Cape and the California appellations of Napa, Sonoma and Santa Barbara

Furthermore, these bodies of water have a moderating effect on the climates of these regions. This results in a generally milder climate which shows fewer temperature extremes and a generally smaller temperature range. This reduced volatility is crucial in consistent, viable wine production.

Whilst travelling through the Mosel Valley, I noticed that many vintners noted that another viticultural bonus to bodies of water is that vineyards planted on the banks of rivers receive the benefit of reflected sunlight and heat. Now whilst I am aware of the solar/reflection properties (known an albedo) of water, and also the concept of black body radiation (limited may it be in water) I could not find any evidence or study to indicate exactly how much this impacts the surrounding area of a body of water. I would be interested to speak with anyone who is aware of any such studies or has an enhanced knowledge of the topic.

In more moderate climates, rivers and lakes can also lend a hand in encouraging the growth of botrytis cinerea. France’s Sauternes, Coteaux du Layon and Tokaji in Hungary are a few examples of sweet wine regions adjacent to rivers. The botrytis cinerea fungus needs warm, humid conditions to take. Rivers and lakes provide, and encourage, the conditions required to facilitate the growth of this fungus.

A further indirect contribution of bodies of water toward the prosperity of surrounding vineyards is wind. Whether this be convection current on the slopes of steep river banks, strong wind from large lakes or sea breezes (if, in some cases, you can call them breezes) Note, at this point, that winds strongly influence viticultural conditions; however, I will discuss within a future independent post.

Furthermore, it is worth noting that the vineyards surrounding many of the great rivers which dissect the worlds great wine regions are usually relatively precipitous. Slopes occur naturally over millennia as rivers carve through the landscape (I am sure the geological explanation to this is much more complex, but we’re here for wine right?) These slopes also have profound effects on a regions viticulture, but I view these as a somewhat secondary relation to rivers and so will cover the importance of slopes in a future post.

So, no matter what your wine of choice, I am almost certain that a body of water has had a profound effect upon it. Hopefully this article has given you a more comprehensive understanding of exactly how this effect comes about. As ever I would love to hear from you and discuss this topic further with anyone who has information which could further develop this post.

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