I have written about and often referred to terroir in past columns. But the question regarding what it really is and if it’s a true component of fine winemaking, continues as a topic of conversation when I’m leading groups on a wine country adventures or tastings. As I’ve said many times, terroir is one of the most commonly used terms in the vocabulary of wine but certainly one of the least understood.

This lack of understanding is most unfortunate because terroir is considered by the vast majority of wine professionals, collectors and authors alike as the driving force in making distinct wines that speak of their place of origin. The term comes from the French terre, meaning land, but there is no precise translation to English.

The concept of terroir extends far beyond just the land where the grapes are grown, taking into consideration the complete environment of the vine itself. In addition to soil composition, the wine grapegrowing and winemaking community also considers the climatic conditions of the area, elevation and grade, exposure, day-to-night (diurnal) temperature variation, rainfall, drainage, wind patterns, relative humidity, daylight hours and other factors that don’t often lend themselves to precise measurement.

Quality wine grapegrowing areas are usually found in places with less fertile soils than those better suited for growing other fruits, vegetables and nuts. These poorer soils and less hospitable growing conditions lead to increased vine stress and decreased vigor yielding grapes that exhibit the specific character needed for the production of fine wine.

In an effort to better understand terroir, countless scientific studies primarily focused on soil composition have been conducted. Yet the lack of consensus and the inability to quantify the soil’s direct relationship to flavor and aroma have lead to inconclusive results that have further blurred the definition of terroir and its importance in wine grapegrowing.

Actually, the realization that the same grape variety did better and exhibited different characteristics in one growing area than another was first noted by the Greeks centuries ago. Later, similar observations were recorded by religious orders in Burgundy and eventually became the basis of France’s Appellation d’origine contrôlée (AOC) and subsequently, all other appellation laws throughout the world, including our AVA designations in the U.S.

Let’s first examine what the scientific community has determined soil does not contribute to a wine’s character. Many studies have shown that the specific flavors and aromatics of wine cannot be directly derived from the soil in which they are grown. It is generally accepted that root systems are incapable of absorbing nutrients and minerals that specifically influence these components. So much for what soil doesn’t determine.

Any conversation on terroir must include soil type as a critical factor affecting the health of the vine and the quality of fruit produced. Different varietals do better in certain soils than others and the same varietal will adapt differently to changes in soil type. As an example, merlot does well in clay where water is retained a bit longer, while cabernet sauvignon much prefers rocky or gravelly soils where the focus is more on drainage.

Both can be grown in either condition but each one does better where it is the happiest. In addition to drainage, differing soil types also impact the vine in other ways. The reflection of heat during the growing season, enabling or resisting root development and storing nutrients are just a few examples.

While soil may be the foundation of terroir, it is by no means the final arbiter.

Wind patterns like those from the cooling breezes off the San Pablo Bay that wend their way through Carneros and up the Napa Valley to the very harsh Mistrals that literally blow (up to 60 mph) through France’s Rhone Valley are a major influence in vine stress, and flavor and aromatic development. From the warmer southwest exposures to the cooler northeast facing vineyards, fruit development differs, influencing many aspects of vine growth from bud break to ripening cycles and harvest times.

A thinner layer of topsoil found on hillsides (especially on steeper grades) causes the roots to fight harder in the rocky subsoil environment, leading to additional stress on the vine and resulting in increased levels of structural intensity.

Vineyards located above the cloud and fog lines experience additional sunlight hours but with typically cooler daytime temperatures and much colder nights that lead to longer “hang times” with slower ripening and later harvests. All these (and more) varying conditions ultimately affect both flavor and aromatic characteristics that are further differentiated by the varietal clone being grown.

It’s easy to see the concept of terroir is somewhat anecdotal. Its effect has been observed and appreciated for centuries, yet much of the objective underlying scientific support lacks definition. Perhaps Dr. Kees van Leewen of the Insitut de Sciences et de Vin in Bordeaux summed it up best by simply saying: “Terroir is all about the interaction of the vine and the natural environment.”

Share your experiences with other readers by commenting on this article at napavalleyregister.com/wine-exchange or email me at allenbalik@savorlifethroughwine.com.

Allen Balik, a Napa resident, has been a wine collector, consultant, author, fundraiser and enthusiast for more than 35 years.