| Where Do the Bubbles Come From? | By |
The process of making sparkling wine in the traditional method of Champagne (Méthod Champenoise) has evolved over the past 300 years since the pioneering work of Dom Perignon. Dom Pérignon, born Pierre Pérignon in 1638, was ordained at the Benedictine Monastery in Verdun. Although nearly blind, the man became an administrator at the Monastery at Haut Villers near Épernay. Noted for his methodical thinking, he observed that the quality and commercial viability of the white still wines of the Champagne region depended on the summer being sunny enough. He pioneered making white wine with black grapes because the black grapes do not depend as heavily on summer being sunny to attain quality ripeness. Along with many other innovations such as blending wines from different vineyards and reintroducing the cork as a wine stopper for the first time since the Romans, Dom Pérignon introduced stronger English bottles to prevent his wine from exploding and produced his first sparkling champagne in the late 1600s.
The first step in making Champagne, like the production of still wine, is the pressing of the ripened grapes. The grapes are picked and sorted for quality. The grapes when harvested are kept in lots according to their vineyard of origin for future blending to achieve a distinctive house style. Massive presses crush the grapes to produce the must (or grape juice). This process is repeated three times to extract the must. The first press called cuvée is the highest in quality and volume accounting for more than 80% of the juice. Subsequent presses contain more tannin and are darker due to longer contact with the dark grape skins of Pinot Noir or Meunier.
The lots of must are transferred to large stainless steel tanks or in some cases wood barrels for the first fermentation. In the process of fermentation the microorganism yeast (Saccharmyces), which naturally exists on the skins of the grapes but is also added to enhance the fermentation process, consume the sugar in the wine. Yeast use the sugar to produce energy to power their cellular processes, keeping them alive. During fermentation, cellular machinery called enzymes in a multi-step process break sugar molecules into smaller pieces. In this process of sugar disassembly, called glycolysis energy is released from the broken sugar molecules and stored in small molecules called adenosine triphosphate (ATP). ATP acts as energy currency that can be used in many different cellular processes that could not directly utilize the energy from sugar. An important step in gylcolysis and for yeast and the wine and bread industries is the enzymatic conversion of pyruvate (a short molecule half the size of its parent sugar molecule) to acetaldehyde. (See the Figure)
Under aerobic conditions pyruvate can be used in the cell in two other energy pathways called the citric acid cycle and the electron transfer reaction. Under low oxygen (anaerobic) conditions, an enzyme called pyruvate decarboxylase cuts a carbon and two oxygens off pyruvate liberating carbon dioxide gas (CO2) and making acetaldehyde, which is then converted to alcohol. Wine left to ferment in aerobic conditions results in vinegar. That is why fermentation of wine takes place in closed containers. Liberated CO2 leavens bread and fills sparkling wine with bubbles. However, these bubbles are released in the first fermentation resulting in an acidic, pale, still wine.
Dom Pérignon and others noticed that when the winter is very cold the wine fermentation would cease but would resume in the bottle when the weather warmed up again. This second fermentation sometimes exploded the bottle from too much CO2 build up but at other times imparted a gentle fizz. Experimentation with bottles with thicker walls and a deep indent in the bottom called a punt and a wire cage to keep the cork in opened the way to very effervescent champagne. Since the CO2 generated by fermentation is released in the first fermentation, sparkling wine gets its bubbles from a second fermentation in the bottle. The wine from the first fermentation is put in a bottle with some yeast and some more sugar for them to eat. This produces CO2, which dissolves into the wine because it cannot escape past the secured cork. Additional alcohol is produced that eventually gets the yeast drunk. Drunk yeast no longer make CO2 and fall to the bottom of the bottle, producing yeast lees. This sealed second fermentation in the bottle of the Méthod Champegnois differentiates this wine from any other with the yeast lees imparting warm toasty qualities unique to champagne made by the Méthod Champegnois.