Understanding the “terroir effect” (Part 1)

by | May 1, 2021 | Viticulture research, Winetech Technical

The taste of any given wine, regardless of cultivar, is inextricably linked to its origin. Environmental factors, such as soil and climate, influence organoleptic characters and by deconstructing measurable soil and climate parameters, this influence on a wine’s typicity can be better understood.

In Part 1 of this two article series a brief introduction on the effect of terroir on wine aroma and an overview of the main families of aromatic grape and wine compounds are given. Part 2 of this series will focus on specifically how terroir shapes grape and wine aroma expression, and the prediction and management of aroma typicity relating to terroir.

Introduction

It has long been acknowledged that wine typicity, or style and quality in other words, depends heavily on where vines grow. Local soil and climate conditions are major influences on wine sensory qualities. It is up to the winegrower to harness optimal plant material and vineyard management practices adapted to site, and the winemaker to use appropriate winemaking techniques according to berry composition, in order to fully shape the terroir effect.

But to go further than merely a descriptive link between wine typicity, soil and climate, these need to be broken down into measurable parameters. Simply put, the effect of climate can be assessed through the measurement of air temperatures, radiation and rainfall. Similarly, the role of soil can be assessed through the measurement of soil water holding capacity and nitrogen status.

Grape and wine aromas

Wine aromas can be classified as primary (produced during grape ripening), secondary (produced during fermentation) and tertiary (produced during wine ageing), and it follows that their expression is of key importance. Odorous primary aroma compounds are either free (volatile) or bound (conjugated) to other molecules present in grapes and can be liberated during fermentation or ageing. Ester compounds (secondary aroma compounds) are rather abundant depending on wine composition. The hundreds of aromatic compounds that have been identified in wine can be further grouped into specific families.

Green and peppery flavours

Major contributors to green aromas are methoxypyrazines, particularly 2-methoxy-3-isobutylpyrazine (IBMP), which is responsible for green (bell) pepper aroma. C6 compounds also contribute to green aromas and their abundance in wine is modulated by the winemaking protocol followed, but there is not a lot of information available in literature about the impact of environmental factors on their presence in grapes and wines. 1,8-Cineole, a monoterpene, imparts minty flavours to wine and (-)-rotundone, a sesquiterpene, notably contributes peppery aromas to Syrah and other cultivars.

Other monoterpenes

Terpenes can be found as free or glycosylated forms in grapes. They are important contributors to Muscat aromas in grapevine cultivars such as Muscat, Gewürztraminer and Riesling.

Volatile thiols and C13-norisoprenoids

Although the volatile thiols aroma family was first identified in Sauvignon blanc, it is present in numerous other cultivars. They are present in grapes as non-odorous glutathione or cysteine bound precursors and are released, and thereby becoming aromatic, during alcoholic fermentation by yeast. Important volatile thiols are 3-mercaptohexanol (3MH – grapefruit), 3-mercaptohexanol acetate (3MHA – passion fruit) and 4-mercapto-4-methylpentan-2-one (4MMP – boxwood).

C13-norisoprenoids, a family of important wine aroma compounds, include β-damascenone, described by fruity-flowery or baked apple notes and 1,1,6-trimethyl-1,2-dihydronaphtalene (TDN), which imparts kerosene-like notes. The latter compound is characteristically found in older Riesling wines. Megastigmatrienone, also a C13-norisoprenoid, smells of spices and tobacco, and is often referred to as “tabanone”.

Dried fruit aromas

Massoia lactone, γ-nonalactone and furaneol, 3-methyl-2,4-nonanedione (MND), and (Z)-1,5-octadien-3-one have recently been identified as compounds contributing to dried fruit aromas in must and red wines. This family of compounds are specifically associated with over-ripening of grapes and are expressed in wines made from such grapes.

Substituted esters and qualitative fruit aromas

Several studies have demonstrated the sensory impact of substituted esters on fruity expression in red wines, even when these compounds were present at concentrations below their detection thresholds. These esters increase the perception of fruity aromas due to numerous synergistic effects between fruity compounds.

Other aroma compounds and complementary observations

Dimethyl sulphide (DMS) in wine has a varying aroma impact, depending on its concentration. At low concentrations it imparts blackcurrant aroma, at medium concentration truffle or undergrowth, and at high concentration green olive or asparagus. It should be noted that there is a positive link between DMS concentration and the ageing bouquet complexity of the most iconic Bordeaux red wines. DMS does not impart fruit aromas, but it does have an indirect impact on fruity aroma expression, enhancing blackcurrant aromas at low concentrations.

Aromatic N,S-heterocycles, a large family of wine aromatic compounds, contribute a broad spectrum of aromas ranging from meat to cooked potatoes, roasted coffee or hazelnut. O-aminoacetophenone (AAP) is associated with the untypical ageing character of white wines, particularly in Riesling. Wines showing high levels of AAP reminisce of naphthalene, floor polish, acacia blossom or mothballs and display a metallic bitterness on the palate.

Conclusion

It is known that volatile aromatic compounds are not specific to a cultivar, but rather that their concentration varies depending on cultivars. One example of this is Riesling wine that contains more TDN than Chardonnay or Gewürztraminer. Aroma compounds in wine vary considerably with environmental factors such as soil or climate – the influence of cultivar, soil and climatic conditions on a wine’s taste is known as the “terroir effect”.

Part 2 of this series of articles will focus on measurable parameters, such as air temperature and vine water status (to name but a few), and how they impact wine typicity.

Reference

Van Leeuwen, C., Barbe, J., Darriet, P., Geffroy, O., Gomès, E., Guillaumie, S., Helwi, P., Laboyrie, J., Lytra, G., Le Menn, N., Marchand, S., Picard, M., Pons, A., Schüttler, A. & Thibon, C., 2020. Recent advancements in understanding the terroir effect on aromas in grapes and wines. OENO One 4, 985 – 1006.

– For more information, contact Bernard Mocke at bmocke@gmail.com.

 

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