What Terpenes Do Grapes Have? A Comprehensive Guide

Over 50 different terpenic compounds have been identified in grapes and wines, and these potent plant metabolites are the primary source of many of the distinct varietal aromas. The specific types and concentrations of terpenes present are what gives each grape variety its unique aromatic character, influencing everything from subtle floral nuances to intense peppery notes.

Quick Summary

Grapes contain a wide array of terpenes, with dominant types like linalool, geraniol, and nerol providing floral and citrus aromas, particularly in aromatic varieties such as Muscat and Gewürztraminer. Other important terpenes, including rotundone and norisoprenoids, contribute peppery and petrol notes, while numerous minor terpenes work synergistically to create a complex aroma profile.

Key Points

• Linalool, Geraniol, and Nerol: These monoterpenes are major contributors to the intense floral and citrus aromas, especially prominent in Muscat, Gewürztraminer, and Riesling varieties.

• Bound vs. Free Terpenes: Terpenes exist in grapes primarily as odorless, sugar-bound compounds (glycosides) and are released into their volatile, aromatic form during fermentation through hydrolysis.

• Varietal Differences: Different grape varieties possess unique terpene profiles; for instance, rotundone contributes black pepper notes to Syrah, while norisoprenoids like TDN are linked to the petrol aroma in aged Riesling.

• Impact of Environment: Factors such as sunlight exposure, climate (cooler climates help retain delicate compounds), and soil conditions significantly influence the quantity and profile of terpenes in grapes.

• Winemaking's Role: Winemaking techniques, including skin maceration and yeast selection, are crucial for extracting and converting terpenes, ultimately defining the wine's final aroma and flavor profile.

• Subtle Contributions: Even at concentrations below the sensory threshold, terpenes can interact with other aroma compounds to influence the overall flavor and bouquet of a wine.

The Role of Terpenes in Grape Aroma

Terpenes are a vast and diverse class of organic compounds produced by many plants, including grapevines. They are a major contributor to the distinctive aromas and flavors of grapes and, subsequently, wine. These volatile compounds are primarily concentrated in the grape skins, though they can also be found in the flesh of some varieties. Terpene concentration and composition are influenced by several factors, including grape variety (genetics), climate, soil conditions, and viticultural practices such as sun exposure and leaf thinning.

One of the most fascinating aspects of terpenes in grapes is their dual existence. A large proportion of monoterpenes exist as non-volatile, odorless glycosides, which are sugar-bound forms located in the grape must and skin. During winemaking, these glycosides can be released into their free, volatile, and highly aromatic forms through a process called hydrolysis, triggered by enzymes or acids. This enzymatic liberation is a key reason why fermentation and aging transform the grape's subtle aroma into a wine's complex bouquet.

Major Terpene Compounds Found in Grapes

Several terpenes contribute to the aroma of grapes and wine. Their presence varies significantly depending on the grape variety. Notable examples include Linalool (floral/citrus, high in Muscat), Geraniol (rose/citrus, in Gewürztraminer and Muscat), Nerol (sweet rose/citrus), Citronellol (citrus/floral, in Riesling/Gewürztraminer), Rose Oxides (rose/lychee, in Gewürztraminer/Muscat), Rotundone (black pepper, in Syrah/Grüner Veltliner), and Norisoprenoids like TDN (petrol, in aged Riesling). A comparison of terpene profiles across different grape varieties reveals the complexity and diversity of these compounds and their impact on aroma. The full list of compounds and their varietal associations can be found on {Link: Abstrax Hops https://abstraxhops.com/blogs/learn/are-there-terpenes-in-wine-yes}.

Factors Influencing Terpene Content

Beyond the intrinsic genetic makeup of the grape variety, external factors play a crucial role in shaping the final terpene profile:

• Sunlight Exposure: Adequate sunlight exposure can increase monoterpene concentrations, while UV attenuation can impact synthesis.
• Climate: Cooler climates tend to retain more delicate terpene compounds, benefiting varieties known for terpenic character.
• Winemaking Techniques: Extended skin maceration can extract more terpenes, and yeast strains can influence terpene liberation and modification.
• Ripening Stage: Terpene concentrations change during ripening, often peaking during pre-veraison or later stages, which is monitored by winemakers.

Conclusion

The diverse aromas in grapes and wine, from floral to spicy, are significantly influenced by terpenes. Monoterpenes like linalool, geraniol, and nerol contribute to varietal aromas. While genetics determine their presence, factors like climate, sunlight, and winemaking techniques shape their final expression. For more detailed information on terpenes in viticulture and enology, the Waterhouse Lab at UC Davis provides valuable research {Link: Waterhouse Lab - UC Davis https://waterhouse.ucdavis.edu/whats-in-wine/terpenes}. Exploring grape terpenes offers a deeper understanding of the science behind wine's complexity.

Frequently Asked Questions

What is the primary function of terpenes in grapes?

Terpenes primarily contribute to the aroma and flavor of grapes and wine, creating a wide range of sensory experiences including floral, citrus, and spicy notes.

How does terpene content differ between grape varieties?

Terpene content varies significantly depending on the grape variety due to genetic factors. Aromatic varieties like Muscat and Gewürztraminer have high levels of prominent monoterpenes, while neutral varieties have much lower concentrations.

What causes the 'petrol' smell in Riesling wine?

The 'petrol' aroma in aged Riesling comes from a norisoprenoid compound called TDN (1,1,6-trimethyl-1,2-dihydronaphthalene), which is derived from the degradation of carotenoids in the grape skin.

How does sun exposure affect grape terpenes?

Adequate sunlight exposure, especially on the grape bunches, can increase the concentration of monoterpenes. Conversely, shading can lead to lower levels of these compounds.

What is the difference between free and bound terpenes?

Free terpenes are volatile and directly contribute to aroma. Bound terpenes are non-volatile, odorless glycosides, which can be released into their aromatic form during winemaking via hydrolysis.

Can terpenes have health benefits?

Yes, some monoterpenes found in grapes and wine, such as linalool, have been studied for potential health benefits, including antimicrobial, anti-inflammatory, and antioxidant properties.

Which winemaking techniques can influence terpene levels?

Techniques like extended skin contact can increase the extraction of terpenes from grape skins. The choice of yeast strain during fermentation can also affect the release and modification of terpenes.