Terroir            (From The New Sotheby’s Wine Encyclopedia, 4^th Edition)

There are certain, constant factors that affect the taste and quality of wine. These include location; climate, which

determines the ability to grow grapes; vintage, the vagaries of which can make or break a harvest; aspect, responsible for enhancing or negating local conditions; and soil. All these factors are discussed in more detail below and can be classified as elements of terroir.  Also important, of course, are viticulture, because the cultivation techniques used can stretch or concentrate varietal character (see pp.19–22); vinification, which, like cooking methods, can produce a range of options from the same basic ingredient (see pp.25–31); the winemaker, the idiosyncratic joker in the pack; and grape variety—always the most important factor (see pp.35–45).

 

Location

The location of a vineyard is fundamental in determining whether its climate is suitable for viticulture. Virtually all the world’s wineproducing areas, in both hemispheres, are located in the temperate zones between 30° and 50° latitude, where the annual mean  temperature is between 10°C (50°F) and 20°C (68°F). The most northerly vineyards of Germany are at the outermost limit of this range, between 50° and 51° latitude (almost 53º if we include the scattered vineyards of former East Germany), but they survive because of the continental climatic influence, which assures hotter summers. The shorter days also retard the cane growth in favor of fruit maturity, allowing the grapes to ripen before the harsh continental winter. Interestingly, most of the world’s finest wines  are produced in west-coast locations, which tend to be cooler and less humid than east-coast areas. Forests and mountain ranges protect the vines from wind and rain. A relatively close proximity to forests and large masses of water can influence the climate through transpiration and evaporation, providing welcome humidity in times of drought, although they can also encourage rot. Thus some factors can have both positive and negative effects.

 

Climate

Climate and weather are the most important factors that influence the growth of grapes for high-quality wines. Climate is determined by geographical location, whereas weather is the result of how nature decides to affect that climate on a daily basis. In other words, climate is what it should be, weather is what it is. A grower must select a region with an amenable climate and hope that nature does not inflict too many anomalies. Although some vines survive under extreme conditions, most—and all classic—winemaking vines are confined to two relatively narrow climatic bands between 30º and 50º latitude and require a combination of heat, sunshine, rain, and frost.

 

Heat

Vines will not provide grapes suitable for winemaking if the annual mean temperature is less than 50°F (10°C). The ideal mean temperature is 57º to 59°F (14º to 15°C), with an average of no less than 66°F (19°C) in the summer and 30°F (-1°C) in the winter. In order for the vines to produce a good crop of ripe grapes, the minimum heat-summation, measured in “degree-days” with an average of above 50°F (10°C) over the growing season, is 1,800º (using °F to calculate) or 1,000º (using °C to calculate).  Below are the degree-day totals over the growing season for a variety of vineyards from around the world.

 

Sunshine

While light is required for photosynthesis, the most important biological process of green plants, there is sufficient light for this even in cloudy conditions. For vinegrowing, however, sunshine is needed more for its heat than its light. Approximately 1,300 hours is the minimum amount of sunshine required per growing season, but 1,500 hours is preferable.

 

Rainfall

A vine requires 27 inches (68 centimeters) of rain per year. Ideally, most of the rain should fall in the spring and the winter, but some is needed in the summer too. Vines can survive with less water if the temperature is higher, although rain in warm conditions is more harmful than rain in cool conditions. A little rain a few days before the harvest will wash the grapes of any sprays, and is therefore ideal if followed by sun and a gentle, drying breeze. Torrential rain, however, can split berries and cause fungus.

 

Frost

Surprising as it may seem, some frost is desirable, providing it is in the winter, since it hardens the wood and kills spores and pests that the bark may be harboring. However, frost can literally kill a vine, particularly at bud-break and flowering (see p.23).

 

Vintage

The anomalies of a vintage can bring disaster to reliable vineyards and produce miracles in unreliable ones. A vintage is made by weather, as opposed to climate. While the climate may be generally good, uncommon weather conditions can sometimes occur. In addition to this, the vintage’s annual climatic adjustment can be very selective; on the edge of a summer hail storm, for example, some vineyards may be destroyed and produce no wine at all, while others are virtually unharmed and produce good wine. Vines situated between the two might be left with a partial crop of fruit that could result in wines of an exceptional quality if given a further two to three months of warm sunshine before the harvest, because reduced yields per vine produce grapes with a greater concentration of flavor.

 

Aspect

The aspect of a vineyard refers to its general topography—which direction the vines face, the angle and height of any slope, and so

on—and how this interrelates with the climate.  There are few places in the world where winemaking grapes—as opposed to table grapes—are successfully grown under the full effect of a prevailing climate. The basic climatic requirements of the vine are usually achieved by manipulating local conditions, keeping sunshine, sun strength, drainage, and temperature inopes (north-facing in the southern hemisphere) attract more hours of sunshine and are therefore cultivated in cooler areas.  In hotter regions, the opposite facing slopes tend to be cultivated.

 

Sun Strength and Drainage

Because of the angle, vines on a slope absorb the greater strength of the sun’s rays. In temperate regions the sun is not directly overhead, even at noon, and therefore its rays fall more or less perpendicular to a slope. Conversely, on flat ground the sun’s rays are dissipated across a wider area, so their strength is diluted. (The plains are also susceptible to flooding and have soils that are usually too fertile, yielding larger crops of correspondingly inferior fruit). Lake- and river-valley slopes are particularly well suited for vines because they also receive rays reflected from the water.  A sloping vineyard also affords natural drainage. However, hilltop vines are too exposed to wind and rain and their presence, instead of a forest covering, deprives vines below of protection. Forested hilltops not only supply humidity in times of drought, but absorb the worst of any torrential rain that could wash away the topsoil below.

 

Temperature

While slopes are very desirable sites, it must be remembered that every 330 feet (100 meters) above sea level, the temperature falls

1.8°F (1°C). This can result in an extra 10 to 15 days being needed for the grapes to ripen and, because of the extra time, the acidity

will be relatively higher. Thus a vineyard’s altitude can be a very effective way of manipulating the quality and character of its crop.

Riverside and lakeside slopes also have the advantages of reflected sunlight and the water acting as a heat reservoir, releasing heat at night that has been stored during the day. This not only reduces sudden drops in temperature that can be harmful, but also the

risk of frost. However, depressions in slopes and the very bottoms of valleys collect cold air, are frost-prone, and retard growth.

 

Soil

Topsoil is of primary importance to the vine because it supports most of its root system, including most of the feeding network. Subsoil always remains geologically true. Main roots penetrate several layers of subsoil, whose structure influences drainage, the root system’s depth, and its ability to collect minerals. The metabolism of the vine is well known, and the interaction between it and the soil is generally understood. The ideal medium in which to grow vines for wine production is one that has a relatively thin topsoil and an easily penetrable (and therefore well-drained) subsoil with good water-retaining characteristics. The vine does not like “wet feet,” so drainage is vital, yet it needs access to moisture, so access to a soil with good water-retention is also important. The temperature potential of a soil, its heat retaining capacity, and its heat-reflective characteristics affect the ripening period of grapes: warm soils (gravel, sand, loam) advance ripening, while cold soils (clay) retard it. Chalk falls between these two extremes, and dark, dry soils are obviously warmer than light, wet soils. High-pH (alkaline) soils, such as chalk, encourage the vine’s metabolism to produce sap and grape juice with a relatively high acid content. The continual use of fertilizers has lowered the

pH level of some viticultural areas in France, and these are now producing wines of higher pH (less acidity).

 

The Mineral Requirements of the Vine

Just as various garden flowers, shrubs, and vegetables perform better in one soil type as opposed to another, so too do different grape varieties. Certain minerals essential to plant growth are found in various soils. Apart from hydrogen and oxygen (which are supplied as water) the most important soil nutrients are nitrogen, which is used in the production of a plant’s green matter; phosphate, which directly encourages root development and indirectly promotes an earlier ripening of the grapes (an excess inhibits the uptake of magnesium); potassium, which improves the vine’s metabolism, enriches the sap, and is essential for the development of the following year’s crop; iron, which is indispensable for photosynthesis (a lack of iron will cause chlorosis); magnesium, which is the only mineral constituent of the chlorophyll molecule (lack of magnesium also causes chlorosis); and calcium, which feeds the root system, neutralizes acidity, and helps create a friable soil structure (although an excess of calcium restricts the vine’s ability to extract iron from the soil and therefore causes chlorosis). For information on specific soil types, see pp.17–18.