The acids found in wine include lactic, acetic, succinic, and other acids that form during the wine-making process, as well as the tartaric, citric, and malic acids that are already found in the grapes. These six acids are wine's main organic acids.
There is a relatively small amount of tartaric acid in wine, but it can sometimes have a negative effect on fragrance when, through the work of bacteria, acetic acid and diacetyl are produced.
Found in abundance in apples and grapes, malic acid is transformed into lactic acid by MLF (malolactic fermentation) and reduces. Malic acid is found in large quantities in German wine, which does not undergo MLF. Malolactic fermentation is a fermentation process by which lactic acid and carbon dioxide are created when lactic acid bacteria eats malic acid. This process is undergone in order to add a mellowness and complexity to the flavor of the wine and to strengthen the stability of the microorganisms in the wine.
There is a relatively small amount of citric acid in wine, but it can sometimes have a negative effect on fragrance when, through the work of bacteria, acetic acid and diacetyl are produced.
Because lactic acid is produced by MLF, unlike malic acid it is found in large quantities in red wine that has undergone MLF and in small quantities in German wine.
Acetic acid causes volatility and foul smells or flavors. It is produced when the temperature during fermentation is too high or by bacteria.
Succinic acid brings a slight saltiness and bitterness and is found in Japanese sake.
There are two methods of measuring acidity. One method, known as total acidity, measures the total amount of acid. The other method, pH, measures the properties of the acid.
Total acidity is the sum of the volatile and non-volatile acids, and the unit is in g/L, excluding some situations. The standard for total acidity is different depending on the country—in France it is a value converted into sulphuric acid, in Germany it is a value converted into the amount of hydrogen ions in one liter of water, and in Italy, the United States, Australia, New Zealand, and other counties it is expressed as an amount of tartaric acid. ATAGO's Brix-Acidity Meter PAL-BX/ACID2 for wine displays the total acidity converted into tartaric acid. The pH measurement, on the other hand, is expressed as the concentration of hydrogen ions dissolved in the wine. The pH of wine is normally within the 3–4 range, and the ideal range is 3.2–3.5. The lower the pH value, the higher the acidity, giving off a sour flavor. One number value difference on the pH scale means a tenfold difference in the concentration of hydrogen ions. So, a pH level of 3 and a pH level of 4 would have concentrations with a tenfold difference. A lower pH value (higher concentration of hydrogen ions) brings about better results in the wine-making process.