Titratable acidity, sometimes referred to as fixed acidity, is a measurement of the total concentration of titratable acids and free hydrogen ions present in your wine. A litmus paper can be used to identify whether a given solution is acidic or basic. The most common titratable acids are tartaric, malic, citric and carbonic acid. These acids, along with many more in smaller quantities, either occur naturally in the grapes or are created through the fermentation process.

Volatile acidity is mostly caused by bacteria in the wine creating acetic acid — the acid that gives vinegar its characteristic flavor and aroma — and its byproduct, ethyl acetate. Volatile acidity could be an indicator of spoilage, or errors in the manufacturing processes — caused by things like damaged grapes, wine exposed to air, and so on. This causes acetic acid bacteria to enter and thrive, and give rise to unpleasant tastes and smells. Wine experts can often tell this just by smelling it!

Citric acid is generally found in very small quantities in wine grapes. It acts as a preservative and is added to wines to increase acidity, complement a specific flavor or prevent ferric hazes. It can be added to finished wines to increase acidity and give a “fresh” flavor. Excess addition, however, can ruin the taste.

Residual Sugar, or RS for short, refers to any natural grape sugars that are leftover after fermentation ceases (whether on purpose or not). The juice of wine grapes starts out intensely sweet, and fermentation uses up that sugar as the yeasts feast upon it. During winemaking, yeast typically converts all the sugar into alcohol making a dry wine. However, sometimes not all the sugar is fermented by the yeast, leaving some sweetness leftover. To make a wine that tastes good, the key is to have a perfect balance between the sweetness and the sourness in the drink.

The amount of chlorides present in a wine is usually an indicator of its “saltiness.” This is usually influenced by the territory where the wine grapes grew, cultivation methods, and also the grape type. Too much saltiness is considered undesirable. The right proportion can make the wine more savory.

Sulfur dioxide exists in wine in free and bound forms, and the combinations are referred to as total SO2. It’s the most common preservative used, usually added by wine makers to protect the wine from negative effects of exposure to air and oxygen. Wines with added sulphur dioxide contents usually have “Contains Sulphites” on their labels. It acts as a sanitizing agent — adding it usually kills unwanted bacteria or yeast that might enter the wine and spoil its taste and aroma. It was first used in winemaking by the Romans, when they discovered that burning sulfur candles inside empty wine vessels keeps them fresh and free from vinegar smell. Pretty neat, huh?

Also known as specific gravity, it can be used to measure the alcohol concentration in wines. During fermentation, the sugar in the juice is converted into ethanol with carbon dioxide as a waste gas. Monitoring the density during the process allows for optimal control of this conversion step for highest quality wines. Sweeter wines generally have higher densities.

PH is the measure of the degree of relative acidity versus the relative alkalinity of any liquid, on a scale of 0 to 14, with 7 being neutral. Winemakers use pH as a way to measure ripeness in relation to acidity. Low pH wines will taste tart and crisp, while higher pH wines are more susceptible to bacterial growth.

Sulfates are salts of sulfuric acid. They aren’t involved in wine production, but some beer makers use calcium sulfate — also known as brewers’ gypsum — to correct mineral deficiencies in water during the brewing process. It also adds a bit of a “sharp” taste.

Alcohol is formed as a result of yeast converting sugar during the fermentation process.