Did You Know - Wines are Heavily Influenced by Esters, Isoprenoids, Thiols and Phenols?

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Winemaking is a fascinating blend of science and art. We’ll dive deeper into the art of winemaking in a future blog, but for now, let’s explore some of the chemistry behind it.

During the winemaking process, several chemical compounds are produced that can greatly impact the wine’s aroma and flavor. These compounds include esters, isoprenoids, thiols, and phenols. Let’s take a closer look at each of them:

Esters

Esters are organic compounds formed by the interaction of alcohols and acids during fermentation and as a wine ages in the bottle. They are responsible for fruity, floral, and sweet aromas in wine.

  • Common Esters in Wine:

    • Ethyl Acetate: Produces fruity aromas (or major wine faults!).

    • Isoamyl Acetate: Responsible for pear drop candy flavors and banana-like aromas (Especially Nouveau Beaujolais)

    • Ethyl Hexanoate: Yields pineapple, apple, or pear-like aromas.

    • Phenylethyl Acetate: Gives floral (e.g., rose), fruity and honey-like aromas.

Isoprenoids

Isoprenoids, also known as terpenoids, are aromatic compounds found in wine. They contribute to floral, herbal, and citrusy notes. Certain grape varieties are more prone to producing specific isoprenoids, which is why some wines are renowned for their distinctive floral or citrus aromas..

  • Examples of Isoprenoids in Wine:

    • Linalool: Creates a floral, lavender-like scent (Esp. in Muscat and Gewürztraminer)

    • Geraniol: Yields a floral (rose-like) scent, found in many white wines.

    • Citrus terpenes (limonene): Contributes to citrusy aromas (Esp. in Sauvignon Blanc)

Thiols

Thiols, also known as mercaptans, are sulfur-containing compounds that can both enhance and detract from wine’s aroma. In small amounts, they impart complex, fruity, and tropical notes, reminiscent of passion fruit, grapefruit, or guava (particularly in white wines).

However, thiols can also contribute unpleasant aromas when present in higher concentrations, often associated with the “rotten egg” smell indicative of sulfur contamination..

  • Key Thiols in Wine:

    • 3-Mercaptohexanol: This compound is responsible for grapefruit, passion fruit, and boxwood aromas (Esp. in Sauvignon Blanc)

    • 4-Mercapto-4-methyl-2-penatanone: Contributes to tropical fruit aromas (Esp. in Sauvignon wines)

Phenols

Phenolic compounds, a diverse group of chemical compounds, encompass both volatile and non-volatile components. In wine, they primarily contribute to astringency, bitterness, and color. Additionally, they enhance the wine’s aging potential and are often associated with potential health benefits. Phenols can originate from grape skins and seeds, as well as from oak barrels utilized in winemaking processes.

  • Flavonoids (e.g., anthocyanins): Contributes to the color of red wines and potential health benefits.

  • Tannins: These are found mainly in red wines, and they contribute to the mouthfeel and the structure of the wine.

  • Resveratrol: Known for its potential health benefits, resveratrol is a phenolic compound found in the skin of red grapes and has antioxidant properties.

So, in summary, esters contribute fruity and floral aromas, isoprenoids add distinctive floral and citrus notes, thiols impart tropical and fruity characteristics, and phenols influence color, taste, mouthfeel, and aging potential. Each of these compounds plays a crucial role in shaping the complexity and character of wine, with their levels and interactions being influenced by grape variety, terroir, and winemaking techniques.

Ever Wonder? What Exactly is in Wine?

We know that wine is a lovely drink made from fermented fruit, but what exactly is in a bottle of wine?

Water

Wine is usually comprised of 80-90% water that is directly extracted from squeezed grapes. In rare instances, water may be added to dilute the wine when the alcohol content (or potential alcohol) and/or phenolics become excessive. However, this practice is quite uncommon.

Alcohol

Between 10% and 15% of wine consists of alcohol, specifically ethyl alcohol (also known as ethanol), which is the primary alcohol component in wine. Other alcohols, such as glycerol and methyl alcohol (also known as methanol), may also be present in wine. Why is alcohol significant in wine? It imparts a “body” and “weight” to the palate, providing a tactile sensation as the wine’s elements linger in the mouth. Ethanol plays a crucial role in your nose as well, as it evaporates rapidly and carries the wine’s aromas up to your olfactory receptors.

Acid

The amount of acid in wine typically ranges between 4 to 8 grams per liter (g/L). To put this in perspective, a bottle of wine is 750 ml or 3/4 of a liter. Thus, a typical bottle of wine has 3-6 gm of acid. This level can vary based on the style of wine, grape variety, and region of production.

Tartaric acid is the most common acid found in wine.

Sugar

Most wines, including common varieties like Cabernet Sauvignon, Chardonnay, and Merlot contain less than 4 g/L of residual sugar or less than 3 gm. Glucose and fructose are the two simple sugars that can be found in equal amounts in the grapes. At harvest, grapes typically contain about 15 – 28% sugar. These sugars are highly fermentable, and the yeast converts these sugars into ethanol, making grape juice into wine.

Phenolic Compounds

This gets a bit technical, so hang in there. Phenolic compounds are tiny molecules, called polyphenols and phenolics and they can really make a difference in wine. Some of these compounds include anthocyanins, flavanols, tannins, and vanilla. We know that vanilla aromas and flavors come from oak barrels and tannins come from the skin, stems, and seeds of the grapes. But, the other compounds affect the wine’s color. Anthocyanins are the ones that give red wine its color. The more anthocyanins there are and the less acidic the wine is, the redder it will be. Flavanols are yellow pigments found in white wines. These compounds are sensitive to light, which helps wine look more golden in warmer climates compared to cooler climates.

So, there you have it! Wine is primarily composed of water, along with some alcohol, acids, sugar, and phenolic compounds. When a wine tastes ‘off,’ it’s typically due to an imbalance in these components. Acquiring the right balance is challenging, which is what makes winemaking such a captivating art. Cheers!

What are Lees in Winemaking?

A wine barrel with a clear end-cap shows the settled Fine Lees

I was recently hosting a wine tasting that involved a white wine. On the back label, it stated that the wine had been “Aged on lees.”  I was asked the obvious question “What are lees?”

In the broadest sense, “lees” refers to all the stuff that settles on the bottom of a wine fermentation or aging vessel (e.g., the tank or barrel). This “stuff” can include grape skin fragments, grape seeds, grape stems, pieces if grape leaves and, after fermentation, dead yeast. 

This collection of “stuff” is generally referred to as the “Gross Lees.” Not exactly because it might be considered ‘gross’ in its consistency, but because it is not the collection of stuff that you want your wine to be aged on. These items can to lead to some rather offense odors and flavors in a wine.

Wine makers generally “rack off” their wine (transfer it) to a fresh vessel or barrel that leaves behind the really chunky stuff and only moves the fermented wine, along with a bunch of dead yeast cells that don’t readily settle and remain mixed in with the newly fermented wine.  With aging, the dead yeast cells do settle to the bottom of the tank or barrel (see image).

When a wine is “Aged on Lees,” this contact with the dead yeast cell is allowed to continue throughout the aging process or until the wine maker determines they’ve achieved the desired wine characteristic. Wine makers even encourage the wine’s contact with the dead yeast cells, or “Fine Lees” by stirring the wine to move the lees off the bottom so that it can have more contact with the wine. The French term for this stirring technique is “Bâttonage.”

As the dead yeast cells break down during aging, they can bring out flavors of nuts, honey, bread, etc. They can also bind with tannins in the wine and to help smooth out the wine. So then, when the wine maker is happy with their wine’s characteristics, they let the Fine Lees settle and again carefully transfer (rack off) the wine and leave behind the layer of dead yeast cells that lay on the bottom of the aging vessel. 

It’s Veraison Time in the Vineyards!

Image by Photo by Kelsey Caroline on Pexels.com

The grape growing cycle is currently at the point where berries (the actual term for individual grapes) begin to turn color. This marks the point at which the grape vines move from berry growth to berry ripening.

The term for this stage is called Veraison (vuh-rey-zhun). And this means that there is now approximately 45 days until the beginning of harvest.

While veraison is most obvious on red wine grapes, white grapes also go through veraison. While their color change isn't as dramatic as the reds, they do change from green to a more yellow or golden green. 

Veraison marks the point where the grapes stop growing in size. But, it's also when the sugar content of the grapes increases significantly. And, the acid begins to decline.

So, winemakers are now very closely watching and testing the grapes to find the point where the sugar content and acidity are just right for the particular wine they are trying to produce.

It's an exciting time in the vineyard and harvest is just around the corner! Cheers!