Wine is made up of the following major components:
- Water – Water comes from the grape itself and is typically 80% to 90% of the volume of a wine.
- Alcohol – Alcohol is a product of the fermentation process. It averages between 10% to 15% depending on the variety of grape and the winemaker’s choices.
- Ethyl alcohol (ethanol) is the primary result of fermentation and the main alcohol in wine.
- Glycerol and methyl alcohol (methanol) are secondary types of alcohol, as well as a group of compounds known as fusel alcohols (fusel oils) or higher alcohols.
- Acid – 0.5% to .075%. Acids contribute to the structure and balance of a wine. The most common types of acid are:
- Tartaric acid – The most prevalent type of acid. It is also the strongest in pH. At lower temperatures tartaric acid can form crystals known as “wine diamonds”. Although not considered a defect they are not soluble and can reduce the overall acidity of a wine.
- Malic acid – This acid is sharp-tasting and frequently associated with green apples. Under-ripe or cool climate grapes are usually higher in malic acid. More ripe or warm climate grapes are lower.
- Citric acid – Exists in very low quantities and has no sensory impact on the majority of wines.
- Lactic acid – Not found in grapes but is created in wine by lactic acid bacteria, which convert malic acid into lactic acid through the process of malolactic fermentation. Wines that undergo that fermentation tend to be softer and smoother, and often have a creamy or buttery texture.
- Acetic acid – The acid found in vinegar. Acetic acid is typically created during fermentation. Being volatile it readily evaporates and contributes to the nose of a wine. In higher concentrations, usually the result of chemical reactions between oxygen and ethanol caused by bacteria called acetobacter, it can be unpleasant.
- Succinic acid – A minor component in grapes and by-product of fermentation, succinic acid can have a sharp, bitter, and salty flavor.
- Total Acidity and pH – Two numbers used to describe the acidity level of a wine.
- Total acidity (TA) – The volume of all acids in a wine.
- pH – Represents the combined strength of all acids present.
- Wine usually measures between 2.9 and 3.9 on the logarithmic pH scale.
- Lower pH indicates a stronger acid content.
- Both numbers are needed to get a complete picture of a wine’s acidity, but wine winemakers typically focus on pH, as it gives an indication of stability and plays a role in determining sulfur levels.
- Sugar – Grapes typically contains 15% to 28% sugar at harvest.
- Two types of sugars are found in grapes: glucose and fructose.
- Both types are highly fermentable monosaccharides (simple sugars).
- During fermentation, yeast converts these sugars into ethanol.
- Wines where fermentation is allowed to complete (i.e. all sugar has been converted to alcohol) are considered dry.
- Wines which have the fermentation interrupted before all sugars are converted are considered off-dry or sweet, depending on how much sugar has been left in the wine.
- Some dessert wines can have as much as 24% residual sugar content.
- A small amount of residual sugar can balance high acidity (or vice versa).
- Sweetness can also be used by the winemaker to hide a wine’s flaws.
- Phenolic Compounds – Phenolic compounds (also known as phenolics, polyphenolics, or polyphenols) occur in minute quantities but can have a major impact on the sensory profile of a wine. Phenolics include the following:
- Anthocyanins – Contribute color to red wines. The color is influenced by both the amount of anthocyanins and acidity level. More acidic wines appear redder, less acidic appear bluer (or purple).
- Flavonols – Yellow pigments found in white wines. Flavonols (flavones) increase in grapes with increased exposure to sunlight. White wines from summer climates tend to have a more golden color than grapes from cooler climates.
- Tannins – Astringent, bitter compounds found in skins, seeds and stems. Also found in oak. These components form part of the structure, or backbone, of a red wine. They are also a natural preservative.
- Vanillin – An aromatic phenolic compound in oak. Imparts a vanilla scent to barrel-aged wines. Vanillin increases with the level of “toast” a barrel is seasoned with prior to use.
- Resveratrol – A compound in wine believed to have beneficial health effects.
- Other Components
- Aldehydes – Oxidized alcohols formed when wine is exposed to air. Most common is acetaldehyde, formed by oxidation of ethanol. Acetaldehyde contributes to the aroma in Fino Sherry.
- Esters – Molecules that are the result from joining of acid and an alcohol. One of the most common esters is ethyl acetate, the ester of acetic acid and ethanol. At low concentrations, it imparts a fruity, flowery aroma. At high concentrations It may impart aromas of nail polish remover, varnish, or glue.
- Dissolved gases – In wine, dissolved oxygen promotes the chemical process known as oxidation. Another dissolved gas commonly found in wine is CO2. This is a natural by-product of fermentation.
- Sulfites – A class of chemicals based on sulfur, an important preservative to keep wine stable after fermentation. It is also produced in small quantities as a by-product of fermentation. It is an antioxidant and an antibacterial agent. In the US, wine containing more than 10 parts per million sulfur dioxide is required to display “Contains Sulfites” on the label.