Carbonic acid

In common parlance, the carbon dioxide (CO2) in sparkling wine is commonly referred to as carbonic acid (H2CO3), although only a relatively small proportion of the carbon dioxide (CO2 )physically dissolved in the wine actually 'marries' with the water or causes actual carbonic acid (H2CO3).

As the name suggests, carbonic acid has a slightly acidic effect. This in turn influences the perceived sweetness of a sparkling wine (the state-permitted limits for residual sugar values can therefore be higher for sparkling wines due to the relatively high carbonic acid content).

Carbonic acid also accentuates some of the taste components of a wine, such as acids and tannins. For this reason, many connoisseurs avoid drinking certain mineral waters before or during a tasting, because on the one hand they are often not neutral in taste (minerals) and on the other hand they contain more or less carbonic acid. The carbonic acid consequently influences the taste perception of the tasted wine. The wine could thus appear more tart or acidic than it actually is in terms of acidity. Consequently, mineral waters with minimal (or no) carbonation and at the same time weakly mineralized (less than 500 milligrams of minerals per liter) are often preferred. Many wine enthusiasts also simply stick to tasteless tap water before/during a tasting. Tasting sparkling wines (or even a 'cola') after opening a few days later without carbonation illustrates just how decisive CO2 and carbon dioxide are in terms of taste. The carbonic acid quickly dissipates. As soon as the sparkling wine is stale (worn out, dead, passé, 'flat'...), it seems (sometimes considerably) sweeter.

According to a study by the University of Surrey in Guildford, UK, carbonic acid/CO2 is said to contribute to blood alcohol levels (see links below). One test group was served stale champagne. After five minutes the group with proper champagne had 0.54 per mille, the test group with the stale champagne only 0.39 per mille.

CO2 content is produced in sparkling wines primarily by three processes:
1. by impregnation or the addition of (foreign) CO2 gas.
2. by the first fermentation, whereby CO2 produced during the fermentation of must is kept only partially or entirely in stainless steel tanks.
3. by a second fermentation, whereby an already fermented still wine is transformed into sparkling wine by means of a second fermentation in the bottle (bottle fermentation) or in a stainless steel tank (bulk fermentation).

In the case of champagne (only pure bottle fermentation is permitted), the process is as follows:

After blending, a mixture of wine, sugar and yeast is added to the wine before it is bottled for the second fermentation. This filling dosage ("liqueur de tirage", not to be confused with the dosage made only before the final corking, the "liqueur d'expedition") essentially determines the achievement of the correct carbonic acid content of the final product. Within about seven weeks, the development of the carbonic acid/CO2 is complete. A typical champagne (or sparkling wine) therefore comes to us at about 5-6 bar overpressure, which allows a lot of CO2 (about 9 grams per litre) to be retained in its water-soluble form. Likewise, the CO2 dissolves more advantageously in the cool wine and can be retained longer in the form H2CO3 (one reason why champagne should be served cool). It should also be noted at this point that the custom of the silver spoon in the neck of an opened bottle in the refrigerator offers little to no advantage in terms of preserving the precious bubbles. The advantages of the silver spoon as a heat conductor are trivial. A study in 'New Scientist' magazine tested this with two opened Champagnes (one with a spoon, one without). The perceived carbonic acid/CO2 was exactly the same for both bottles on the following days. Only after more than four days, both champagnes were completely stale or 'flat'.