Uncovering Dionysus’s Wine-Making Secrets

For centuries, humans have been enjoying the flavorful wine. But, it was not magic when Dionysus transformed water in to wine, it involved several, complex chemical reactions between various compounds. Winemaking or vinification is able to produce the aromatic and flavorful wine from the simple grapes we see on vines.

The Raw Materials

The main component of winemaking involves a simple fruit: grapes. However, grapes are not as simple as we think, they have chemical compounds that act as reactants in the complex chemical reactions that occur during winemaking. Commonly used grapes are: Cabernet Franc, Gewürztraminer, Merlot, etc.

Grapes have sugars such as glucose and fructose, which provide the fermentable material for alcohol production. They also have acids like tartaric, malic, and citric acids that contribute to the acidity of the wine. About 70-80% of grapes is water, which acts as a medium for the chemical reactions to take place. Grapes also have volatile compounds and precursors that add flavor and scent to wine. Grapes have phenolic compounds like tannins, anthocyanins and flavonoids which are found in the skin, seeds, and stems of grapes. Tannins and anthocyanins are the key compounds in winemaking.

Tannins are polyphenolic compounds give wine their bitter taste. During fermentation and aging, tannins can polymerize (combine to form larger molecules), which affects the wine's structure and aging potential. Anthocyanin mainly creates the red and purple hues in red wines. At lower pH, wines appear redder, while at higher pH, they take on a bluish hue. Flavonoids contribute to the bitterness and antioxidant properties of wine. These compounds interact with each other, they affect the color stability and intensity of the wine.

Another important component in the winemaking process is: yeast. It converts the sugars in the grape into alcohol and carbon dioxide during fermentation. The most common yeast generally associated with winemaking is Saccharomyces cerevisiae.

Wine also uses preservatives like ascorbic acid and Sulphur dioxide (SO2). They are used to prevent oxidation and microbial spoilage.

The Starting Point

Grapes are commonly harvested during the autumn season. Usually, ripe grapes are used to make sweet wine as the riper the grape is, the more sugar it contains. The climate in which grapes grow also affects the taste of the wine. In cool climates, grapes ripen slowly and to a lesser extent which gives a more tart wine. Likewise, grapes grown in warm climates ripen quickly and to a higher extent, giving a sweeter wine.

After harvesting, the grapes are crushed to release the sugars, acids and some of the polyphenols from the skins (altogether referred to as ‘must’).The must is then filtered using a process called racking, which ensures that all the sediments are gone.

The Fermentation Process

Fermentation is the heart of winemaking. After the grapes have been crushed, the must is transferred to fermentation vessels, where yeast is added to begin the fermentation process. Through the action of yeast, the sugars in grapes are converted into alcohol and carbon dioxide.

In alcoholic fermentation, yeast consumes glucose and fructose in a series of biochemical reactions known as glycolysis, producing compounds like ethanol, carbon dioxide, glycerol, higher alcohols and esters.

In malolactic fermentation, lactic acid bacteria converts malic acid into lactic acid and carbon dioxide. It mainly softens the acidity of the wine and creates a creamier texture and buttery flavors.

Aging and Oxidation

The aging process further develops a wine’s complexity through several chemical reactions. It adds complex flavors and textures to wine. Ageing can occur different vessels, such as oak barrels, stainless steel tanks, and bottles. The type of vessel used for ageing will have a significant impact on the final flavor and aroma of the wine. This phase of the winemaking process normally takes between 6 to 30 months.

During aging, the wine is exposed to the oxygen in the air. This causes the ethanol present to convert in to acetaldehyde. Controlled exposure to oxygen during aging enhances the wine's complexity, developing nutty, toasty, or dried fruit aromas. However, excessive oxidation and use of antioxidants can lead to spoilage, causing undesirable flavors like sherry or vinegar.

Phenolic compounds like tannins and anthocyanins also undergo oxidation. Tannins, oxygen and other molecules combine to form complex tannin structures. The more complex the polymerized tannins, the less astringent the wine is. This causes the wine to become less reactive with the proteins in our saliva, making the wine smoother. Such reactions with phenolic compounds affect both the taste and color of wine. Younger wines have a fruity, tangy flavor with vibrant red-purple colors, while older wines have a nutty, earthy flavor with a brick-red color.

The esters formed from fermentation or the reaction between alcohols and acids continue to develop. They are responsible for fruity and floral aromas in young wines. During aging, these esters can hydrolyze to their constituent alcohols and acids. These alcohols and acids can again undergo esterification to form new esters. Over time, the processes of hydrolysis and esterification balance out, and it creates a drier, nutty flavor.

The vessel in which the wine is aged also affects its flavor. Oak barrels can impart flavors such as vanilla and spice, while stainless steel tanks preserve the fruit flavors and aromas. Oak barrels have lactones, vanillin, and tannins that creates more flavors in the wine. Stainless steel tanks are inert, so they preserve the fruity flavors that are present in young wine.

Before packaging the wine, it undergoes a filtration process called ‘fining’. This process removes unwanted particles that affect the appearance of the wine making it look cloudy or off-color. It uses fining agents such as bentonite, egg whites, gelatin, isinglass, activated carbon or Polyvinylpolypyrrolidone (PVPP).

Bottling the Wine

After the fining process, the wine is bottled into sterile glass wine bottles. Even after packaging the wine in a bottle, the aging process does not stop. It undergoes slow chemical changes in the bottle, including the polymerization of tannins, ester formation, and reduction reactions. These changes can lead to a smoother, more complex wine with time.

The wine bottle has to be stored carefully as it affects the aging process. Vibrations and heat fluctuations can deteriorate a wine’s condition. Wine ages slowly in lower temperature, its optimum temperature, according to experts, being 13°C (55°F). It is not recommended to move wine from a warm room to a cool refrigerator multiple times, as it deteriorates the wine quality. Wine also should not be exposed to direct sunlight as the ultra-violet rays can cause free radicals to develop and unwanted oxidation to occur.

After bottling the wine, the wine is considered to be ‘sick’ as it experiences trauma due to the bottling experience. When bottling, the wine is exposed to oxygen which causes the chemical reactions to fluctuate, making the wine taste different. This period is called ‘bottle shock’. After some time, the wine settles as the oxygen integrates with it. The period of bottle shock varies for each individual wine.

Even if the wine bottle is sterile, the cork’s condition affects the wine. This is also referred to as ‘cork taint’. It can result from the growing conditions of the cork oak, the processing of the cork into stoppers, or the molds growing on the cork itself. The cork transfers off-flavors to the wine during prolonged aging and can be detrimental to the quality of the bottle.

Conclusion

The winemaking process— from grape selection and fermentation to aging and bottling— is full of complex chemical reactions. These reactions create the wine’s flavor, aroma, color, and texture. Each bottle of wine showcases a unique expression of both nature and science. We all now know Dionysus’s winemaking secret, it’s not magic, and it’s chemistry!

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