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Sun + Earth = Terroir?

It is often said that wines are an expression of place and time.  This is an interesting idea. It implies that a wine is a unique combination of geography (place) and weather (time). Some think the French term terroir sums this up. Terroir is claimed by many people to be the magical combination of soil, climate and wine knowhow.  Do you believe in magic! . This page is dedicated to teasing out the effects of climate soils on the wine made. We start by looking at geology. The lay of the land and the soils and rocks that vines grow in. Their are a number of audio interviews that look at the key elements behind Terroir.

The Terroir

Geology and wine (Place)

At the heart of all wine growing regions are the soils and the rocks underneath. But it is the rocks under ground that set the scene for above ground. Some rocks are harder than others and weather differently, harder rocks often form the hills, while softer rocks weather faster and fill valleys. So the rocks beneath control the altitude, orientation and composition of the landscape.

The lay of the land can affect a number of climate issues, for example in Southern England a southerly sloping vineyard will receive up to 30% more sunlight in October compared to a flat vineyard. Not only that, a slope is also beneficial if you are in a wet region as much of the rain water will run off, minimising how much water is absorbed by the rocks and thus is available to the vine.

Rocks that have many small pores can hold water, protecting the vine from periods of drought. While rocks that have cracks throughout, allow water to pass through them, allowing the roots to stay dry. For example heavy clays have high porosity (hold water) but low permeability (ability to pass water).  This results in water soaked roots in wet countries, but in a dry zone they may hold enough water to let the vine have a good drink. Chalk usually has high porosity (holds water) and permeability (passes water) so in wet regions the roots will stay dry but should a drought occur, the vine still has access to water.

Rocks can change the temperature of a region. Large rocks or pebbles heat up during the day, then radiate the heat back into the air at night. You may have noticed this at dusk walking past a brick wall after a hot day, the wall radiates heat onto your face. Regions that have this effect include: Châteauneuf-du-Pape in southern Rhône with its large, smooth round stones (known as pudding stones). In Marlborough New Zealand, the Northern part of the Wairau Valley has stoney soils at the surface from an old river bed. While in Germany the slate in parts of the Mosel (including the Goldtroepfchen) can add heat to the grapes at night, assisting the ripening period. It is often said that cool nights and warm days preserve the acidity in wine. So by having a higher temperature you can expect the acidity to be slightly lower.

The second effect that the surface can have is on the reflectivity of light. Dark soils will absorb light and in particular UV light, while lighter soils and even white rocks, such as chalk, will reflect more light. The effect is similar to skiing on water or snow, where the sunlight reflects off the surface, with many skiers often getting tanned and burnt under their chins. Grapes that are exposed to higher levels of UV light will see a progression of flavour development faster than those that have a low reflectivity. The other effect is that grapes that experience higher UV light will also develop thicker skins and more pigmentation and flavour.

A similar effect to the soil reflecting light is being near a river, where water can refect light on the vines. This occurs often in vineyards in the Mosel region of Germany.

Soils and Rocks

At the surface, soil is made up of a loose covering of broken rock particles enriched with decomposing organic plants and animals.  Soils are often defined by the size of their mineral grains (a mineral is a solid substance that has a crystalline structure). Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. The size of minerals determines the type of soil.

The smallest particle size is called clay and is usually defined as less than 2 micrometres, silt is next usually between 2 and 50 micrometres. Fine sand starts at 50 and by 200 micrometres  it is called course sand. As the size continues to increase it eventually reaches the size of gravel. A mixture of around 40% sand,  40% silt and 20% clay creates a commonly referred to soil type, known as loam. Loam is a perfect base for great soils holding nutrients and organic matter.

The organic matter is often referred to as humus and is responsible for the dark brown or black colour of the soil. Humus is the stable remains of the decayed plant and animal matter. While not well understood, it is thought to be an important part of the fertility of soils, both physically and chemically. Physically, it helps maintain moisture and its spongy structure. Chemically, the humus helps plants access nutrients by providing ions that bind to nutrients, making them more easily accessible to other plants.

Humus is most common in the top soil. Top soil is the top layer of soil usually between 5cm to 1 metre (2 to 24 inches) deep. It contains the most organic matter and is the most biologically active part of the soil. It is also where plants concentrate their roots and obtain the most nutrients. While it may not look as if top soil is changing, it is wrong to think of soils as inert. Weather and biological process change it over centuries. Penetrated by the living then dying roots of plants, bacteria, animal life, fungi, moulds, insects and worms all burrow, break and mix up soils, enriching and making it more porous.

Below the top soil it merges with minerals to create the sub soil. Sub soil often contains clay or loess (windblown sediment). Nutrients are available to plants but may need to be changed first into a more usable form. Below the sub soil is the underlying rock.

There are three types of rocks: Sedimentary, Igneous and Metamorphic.

Sedimentary rocks are formed by layers of small particles forming into solid matter over time. These include sandstone and limestone.

  • Sandstone is a coarse grained sedimentary rock composed mainly of sand-sized mineral or rock grains. Most sandstone is composed of quartz and/or rock forming minerals. Porosity is high enough for sandstone to form aquifers.
  • Limestone is a sedimentary rock composed largely of the calcium carbonate. Mainly formed from marine organisms. It may also include clay silt and sand and also silica. Porosity and permeability are both high.
  • Shale is a fine-grained sedimentary rock whose original constituents were clay minerals or muds. It is characterized by thin laminae breaking with an irregular curving fracture, often splintery and usually parallel to the often-indistinguishable bedding plane. Shale is the most common sedimentary rock.

Igneous rocks are formed from volcanic eruptions. Rocks that are formed by the fast cooling of magma create basalt and rhyolite, while slow cooling forms other types of rock such as granite.

  • Basalt forms when lava flows. It is usually grey to black and fine-grained due to rapid cooling at the Earth's surface . It may contain crystals or have many fine holes (caused by bubbles when the rock cools). 
  • Rhyolite’s form from the cooling of lava at the Earth's surface. Its composition is made up of at least 69% silicon.
  • Granite is a common occurring rock that forms when it cools while still under the surface. It has a medium to coarse texture, occasionally with large crystals. The colours range from pink and grey to black. Granite does not have an internal structure such as layers. Granite has a porosity of less than 0.01
Metamorphic rocks are rocks that are heated and may be subject to high pressure from being buried deep within the earth. The heated rocks create hornfels and granulite, while high temperature and high pressure create slate and schist.
  • Hornfels is a series of rocks that have been baked and have recrystalised  by the heat of molton igneous rock. They can form striking stripes of different fine-grained rocks such as sandstone, shale and slate, limestone and diabase. They are hard, splintery and in some cases, exceedingly tough and durable.
  • Granulite is medium–grained metamorphic rock that has experienced high temperatures, composed mainly of crystallized minerals (quartz) slate. Granulite does not have an internal structure, i.e. no layers.
  • Slate is a fine-grained metamorphic rock, created when high pressure and temperatures under the earth act on shale. Slate is frequently grey in colour, however, slate occurs in a variety of colours even from a single locality
  • Schist is a medium-grade metamorphic rock, forming from rocks that were sedimentary or igneous. The key character is that they have fine alternating layers of different materials and minerals as micas, chlorite, talc, hornblende, graphite and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. By definition, schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and mineral rocks.

Weather and Climate

How cool is your climate? While many people talk about soils, the biggest single factor that affects a wine  after the grape variety is the climate.

If weather is the temperature, rain, sunshine, frost, even ultra violet rays on any particular day, then climate is a longer term average of these weather events. So, while the weather appears random from one day to the next, over the course of a season or year the climate is much more stable.

If we divide the world into two groups, cool climate and warm climate, we get a general feel for the style of wine able to be produced. Cool climate wines often exhibit lower alcohol, higher levels of acidity with fresh clean and defined aromas. Hot climate wines tend to produce wines that are higher in alcohol, lower in acidity and, if the climate is very hot or the grapes have been left on the vine for a long time, stewed baked flavours that can be hard to define.

Once you start to understand the climate of a region you can get a feel for the type of wines that can be made in that region.

By looking at a map below you can start to understand the types of climate in the world. Most vines grow at between 30 and 50 degrees latitude in the Northern and Southern hemisphere. The equator is at 0 degrees and vine growing for wine making starts around 30. Here the climate tends to be hot, but as you move closer to 50 degrees latitude the climate is much cooler.

Now this is a good general rule of thumb, but we can easily improve on this. The closer you are to the sea the more moderate the temperature, as the sea helps to keep the land warm in winter and cooler in summer. Continental areas surrounded by land tend to heat and cool much faster tending to be warmer during the summer growing season and cooler in winter.  

One last general observation, is that west coast regions facing a significant sea or ocean often have more rain than inland and eastern coast regions. This is because the winds that drive much of the world's clouds travel from the west to the east dropping what rain they have when they hit land fall.

To put it all together the map below describes the world's climates on different wine growing regions of the world. You will see that occasionally grapes are grown outside the 30 50 latititude boundary for example England where the Gulf stream keeps us warmer than we normally would be. Other areas can grow grapes at higher latitudes but normally these are at a high altitude where the climate is cooler, such as Australia's Granite Belt in Brisbane.

Where do the flavours in wine come from?

The reasons for unusual flavours in wine are often explained away by saying it is the terroir. But what is the effect of terroir, and how can the terroir affect the flavours in the wine? To start with we need to go back and understand how grapes ripen and flavours develop in the grapes.

As grapes ripen there are a number of different processes going on. Sugars increase and acidity levels decrease. The molecules that create flavours develop and change as part of the normal ripening process. The question is, what set of flavour profiles does the typical grape go though on the way to maturity, and secondly is it possible for the environment to change the typical genetic profile of flavours that a grape may develop?

To answer this it must be remembered that the flavours in the final wine are typically not in the grape when the grape is picked. The grape at harvest has flavour precursors, these are molecules that will change during fermentation and ageing to form the flavours in the wine. However one of the few grape varieties that tastes the same as the wine itself is Sauvignon Blanc (this is because your saliva contains important, precursor chemicals that are needed by Sauvignon Blanc flavours to develop in your mouth). With Sauvignon Blanc the flavours in the grape that form as the grapes mature are:

  • Grassy / herbaceous
  • Nettles
  • Gooseberry
  • Blackcurrant / currant leaf
  • Ripe citrus
  • Passion fruit
  • Ripe stone fruit

As well as flavours developing, keep in mind that as grapes ripen the acid decreases and sugar levels rise.

Now that we have a rough idea on how the flavour and the sugar and acidity change, what happens if one year it is very hot and the other year very cold? Will the flavours develop faster or slower?

Certainly it is true that grapes given higher levels of light will move through the green herbaceous flavours that can dominate wines coming from cool climates. But this is not the only change, for example looking at Sauvignon Blanc from Marlborough New Zealand versus the much warmer Hawkes Bay Sauvignon Blancs, the wines tend to have a riper more tropical fruit style compared to Marlborough, even with similar alcohol levels. Warmer climates often mean faster sugar development and lower acidity, but since the flavours are also riper it would imply that the flavours develop at a faster pace than the sugars increase and the acids decrease.

We can see in the above example how climate can change the flavours developed in the wine, green flavours can be reduced with more light and the flavours the wine develops will also change depending upon the climate. But the flavours that the grape develops are inherent to the genetics of the grape. What about unusual flavours that don’t normally appear in the wine. This is a very contentious issue, so to answer this we are going to look at the world of flowers. In my garden I grow a hydrangea and the plant produces lovely pink flowers all summer. But in most species of hydrangea the flowers are white. In these species the exact colour often depends on the pH of the soil; acidic soils produce blue flowers, neutral soils produce very pale cream petals, and alkaline soils results in purple or pink flowers, like my hydrangea. The reason for the change is because hydrangeas are one of very few plants that accumulate aluminium. Aluminium is released from acidic soils, and in some species, forms complexes in the hydrangea flower giving them their blue colour. In my case the absence of aluminium due to the alkaline soils leads to pink flowers.

So why all this talk about flowers when we are interested in grapes! Well, Joel Peterson from Ravenswood Vineyard in the California says that “unusual flavours in grapes may occur not because of what is in the soil but what is missing”. In the hydrangea case the lack of aluminium in alkaline soils means that the plant changes colour. If a wine lacks an important ingredient then this may result in it adapting to that missing ingredient, and like the flower changed colour, the flavours could change. After all, colours and flavours and even tannins in wine, are all part of the same grouping of chemicals known as polyphenols. The world of plants has numerous examples of plant adapting to a lack of chemicals, so it stands to reason that the soil can influence the grapes.

It may not just be the lack of a molecule that causes the pant to adapt. The grape vine is one of two biological organisms critical to wine. The other is yeast. Yeast converts sugar into alcohol, and yeast strains can change the flavours in grapes. It is certainly true that a lack of nitrogen during fermentation can result in stressed yeast that metabolises the sugar differently producing different flavours in the wine. But certain yeast strains can also change the flavour, for example wild fermented German Riesling from the Mosel can smell and taste very differently to pure yeast strains used and the rogue yeast, brettanomyces, can give a leather, sweaty saddle smell to wine.

You can see its a complex subject, but in essence the grapes have a set of flavours within the genetics of the vine that change according to the climate and environment or the 'terroir'.

Taste the soil!

While it is possible for a vine to develop unusual flavours due to a deficieny in nutrients, a far more common effect is a change in the way the wine feels in your mouth. There are some clear examples where this occurs, it is just that the reasons for these are more vague. The three soils that have a well demonstrated effect on wine are clay, slate and limestone. Each has an obvious influence over the texture of the wine.

Wines grown on clay tend to exhibit a fatness or richness to them, they can feel heavier in the mouth compared to other types of soil. Both Chardonnay and Sauvignon Blanc have expressed this difference in New Zealand. Chardonnays grown in Nelson's Moutuere Hills have a richness most likely caused by their high clay base. Just to the east of Nelson is Marlborough with a similar climate but growing different varieties. Sauvignon Blanc grown in the southern part of Marlborough's Wairau Valley exhibit a heavier textural mouthfeel again almost certainly from their heavier clay based soils, when compared to elsewhere in the region.

Wines grown on slate appear to have a sharper, more zingy acidity. Some may say it is a mineralty, but the effect is to give an effervesent sharpness to the acidity in the wine. Wines from the Goldtroepfchen in Germany's Mosel exhibit this.

Limestone is often considered to be a good bedrock for wine as it is both permeable (passes water when it is wet) and porous (stores water for when it is dry). But it is not just useful as insurance against the weather, so crucial in Europe where irrigation is banned. Limestone, like slate, gives a sharpness to the acidity, again often described as minerality. Examples of wine on limestone Champagne and Burgundy.

The Winemaker's Influence

The winemaker can influence wine in a number of ways, but some proponents of the concept of terroir believe that the winemaker should be a secondary influence, supporting the view that the best wines are made in the vineyard. These proponents, while advocating that the vineyard speaks for itself, will still significantly change the wine by putting it into oak barrels. Like many things in the wine industry there are many corners fiercely defending their view, in this section we will look at the different decisions that winemakers can make and how these decisions influence the wine.

We begin by looking at wine yeast.

Yeast

Yeast is a single cell organism that through its own metabolic process converts carbohydrates to alcohol and acids. To be precise the two common forms of fermentation in wine are the conversion of sugar  into alcohol, known as alcohol fermentation  but often simply referred to simply as fermentation. The other fermentation for wine is converting the sharp malic acid (think green apples) into softer tasting lactic acid, known commonly as malolactic fermentation. Unlike alcoholic fermentation that uses yeasts, malolactic fermentation occurs through lactic acid bacteria and we will cover later on.

The yeast species Saccharomyces cerevisiae used in alcoholic fermentation has been used in baking and fermenting wine and beers for thousands of years. It has been used in food and wine to enrich our diet by the development of flavours, aromas, textures and to add proteins, amino acids, fatty acids and vitamins. But perhaps the most useful for wine is the preservation through the development of lactic acid and alcohol.

Different types of Saccharomyces cerevisiae can change the flavour, aroma, texture and structure of the wine. It is no wonder that traditionalists believe inoculating the wine by introducing foreign strains of yeasts into their vineyard is a break from terroir. It is true that wines with a range of yeasts which is common in wild fermentations (i.e. no inoculated yeast) will produce a larger range of flavours, compared to inoculated wines. The question is does the lack of control and associated problems outweigh the individuality of a wine? These wild fermentations are not as wild as many believe - if a nearby winery starts using a particular yeast strain it is likely that the yeast will eventually make it into their neighbour's 'wild' fermentation. Yeasts are airborne and mobile after all.

So, given there is yeast everywhere, why inoculate wines? Put simply it creates a more reliable, repeatable wine, often fermenting faster with less problems.  Inoculated wines have a huge population of yeast added at the very beginning of the winemaking process, and while there will be wild yeast in the juice, the population never has a chance competing with huge population of inoculated yeast.

Wild fermentations are an arms race between different yeast species, with some yeast better at the beginning when conditions are different to say, in the middle of the fermentation, when lower nitrogen and higher alchol create very different conditions. Either way there is no guarantee that the wild yeast that dominates the fermentation will be suitable at high alcohol levels towards the end of the fermentation - this can result in a stuck fermentation. With yeasts, it can be helpful to think of the population of a yeast species having momentum during fermentation, with enough momentum a weak yeast at high alcohol will complete the fermentation. Occasionally a yeast population will die out before fermentation is completed, this could be temperature, alcohol level or even nutrient deficiency. Stuck fermentations may need an inoculated yeast that can cope with the specific problem. It is also difficult to restart a stuck fermentation, as a result many wild fermentations are inoculated towards the end, gaining a compromise between complexity and reliability.

Many new world wine producers are moving to wild fermentation as seen in Burgundy, Bordeaux and Italy. This is a risky strategy as they have not had the hundreds of years of building up enormous populations of wild yeast strains that are suitable for their grapes and winemaking style. It is likely that a New World producer in a relatively new region going for wild fermentation will simply use the introduced yeast strain used for the last couple of years, with the uncertainty at final vintage. That said inoculated yeasts are derived from selected wild yeast from the famous wine producing regions of the world.

Different types of yeast change the way the wine tastes, the following is a list of different yeast strain characteristics that winemakers can use to select different types of yeasts.

Vigorous Fermentors are valued because the resulting short fermentation period means the wine is protected by ethanol more quickly, reducing the number of spoilage organisms that can gain a foothold during fermentation.

Ethanol tolerant This name is reserved for yeast that can be fermented above 15% abv. This allows the winemaker to ferment very ripe grapes.

Cold tolerant yeast can normally ferment below 10°C, this is most suitable for white wine making where lower temperatures are more common to preserve aromatics.

SO2 tolerant yeast is usually used if the fruit arrives in the winery in a poor condition and the adding of SO2  is required to preserve the fruit. It should be remembered that malolactic bacteria are sensitive to SO2 so using this may create problems further down the winemaking process.

Apart from yeast with tolerances, yeast can be selected for different fermentation products such that change the mouthfeel and aroma of the wine.  While the word production is used it simply refers to the yeast creating more of these molecules than other types of yeasts.

Ester production During fermentation the yeast can create different esters which are the aromatics responsible for fruity, floral and perfumed aromas. The anount of ester produced varies depending upon the yeast strain and the fermentation conditions.

Glycerol producers increase the mouthfeel with a broader, richer, silkier feeling wine and longer finish.

Polysaacharide producers can contribute to mid palate texture and a richer feel, similar to Glycerol.

Release Mannoproteins are deemed to add to the mouthfeel of a wine.

Beta-glucoside Acidity are most noticeable in wines with relatively high concentrations of terpene compounds such as Gewurztraminer, various Muscats and Sauvignon Blanc. This enzyme activity increases the expression of any grape variety.

Metabolize Malic Acid - some strains can metabolize malic acid, reducing the total acidity and the pH of the final wine without producing buttery flavours conventionally associated with bacterial malolactic fermentations.