Wine Components Flashcards
What are the components of a wine?
Water Alcohol Acids Wine Aromatics Residual Sugars Glycerol Phenolics
What percentage does water account for in wine and why is it critical?
Wine is approximately 85 per cent water by volume depending on the abv, level of residual sugar and other factors. The water is critical for the way a wine flows as a liquid.
Explain what alcohol is in terms of wine component?
Ethanol is formed during fermentation and is the predominant alcohol in wine. It has a slightly sweet smell. Ethanol contributes a sense of sweetness and bitterness, and oral warmth. It also makes a contribution to the fullness of the body of a wine and the mouthfeel. High alcohol levels, 14.5 per cent and above, reduce the volatility of wine aromas and increase the sense of bitterness. Wines with these high alcohol levels must have sufficient fruit concentration to be in balance with the alcohol.
There are also traces of higher alcohols, which have a pungent smell. Both ethanol and higher alcohols contribute to the aromas of wine.
Explain what acid is in terms of wine component?
The principal acids of wine, tartaric acid and malic acid, come from the grape itself. Studies in warm climates have shown that these two make up about two-thirds of the total acidity in wine. Other acids (e.g. lactic acid, acetic acid) are produced in fermentation or malolactic conversion.
Volatile acidity mainly refers to acetic acid (vinegar smell), although some other compounds can contribute. It is present in all wines, generally in low concentrations, and is only a fault when in excess. Acetic acid in turn reacts with the alcohol in the wine and becomes ethyl acetate (nail varnish remover smell), which is also perceived as a fault when in excess.
Acidity contributes to the structure of wine, makes wine refreshing and should be in balance with the fruit concentration and, if present, residual sugar, depending on the style of the wine. High acid also makes wine appear leaner on the palate. Excessive acid will make wine taste tart. Lack of acid will make wine taste flabby.
In wine, total acidity and pH are linked but not exactly correlated. This is due to the buffering effect of other molecules (e.g. potassium). A wine with high acidity would usually have a low pH, and vice versa.
Acidity can be measured and expressed in several ways, but the most common measure is ‘total acidity’, which is the sum of all the acids. Although there are many acids present, the result will usually be expressed as the equivalent of grams per litre (g/l) in tartaric acid. Total acidity in wine is typically in the range of 5.5–8.5 g/l. In France, total acidity may be expressed as sulfuric acid (the ratio between sulfuric acid and tartaric acid is 1:1.5).
If total acidity is measured in g/l, pH is a scale of measurement for the concentration of the effective acidity of a solution. Wines typically have a pH in the range of 3–4. This is an inverse scale, so the lower the number the more concentrated the acidity (and the sharper the wine will taste). The scale is logarithmic, so a pH of 3 is ten times more acidic than a pH of 4. pH level affects a range of key parameters in winemaking. A low pH increases the microbiological stability of wine, increases the effectiveness of SO2, gives red wines a bright red colour and enhances a wine’s ability to age well.
Where do wine aromatics come from?
- Aromas from the grapes
- Aromas created by fermentation due to the presence of aroma precursors in grape must
- Aromas originating from fermentation and its by-products
- Aromas from other sources
Explain aromas from grapes?
- Examples of aromatic compounds that are found in the grapes include methoxypyrazines and rotundone.
Methoxypyrazines occur in the Sauvignon Blanc variety and give a grassy, green pepper aroma. - Rotundone occurs in Syrah and in Grüner Veltliner, producing a pepper aroma.
Explain aromas created by fermentation due to the presence of aroma precursors in grape must?
Aroma precursors are compounds that are not in themselves aromatic but are building blocks which become aromatic during fermentation. For example, many compounds occur in grapes in a form combined with sugar as aroma-less precursors. However, through the process of fermentation they become aromatic.
- Thiols are a category of aromatic compounds that are released during fermentation. An example is 4MMP which gives the box tree aromas in Sauvignon Blanc.
- Terpenes are another category of compounds that are formed in this way. They are widely found in wines, giving fruity and floral aromas. Examples include linalool and geraniol contribute to the grapey aromas/flavours in Muscat.
Explain aromas originating from fermentation and its by-products?
Some aromas do not originate from the grapes but are created from fermentation and its by- products, such as lees.
- Esters are compounds which are formed by the reaction of certain acids and alcohols. The majority are created through the action of yeasts in the fermentation process. Esters are responsible for many fresh and fruity aromas and are therefore essential in the aroma profiles of young wines. They are especially important in the aroma of young white wine. The most common ester is isoamyl acetate, which gives aromas of banana when its concentration is high (for example in Beaujolais Nouveau), but others produce apple, pineapple and many other aromas. Another common ester is ethyl acetate, see Acids. Most esters are unstable and will breakdown a few months after fermentation.
- Acetaldehyde occurs in wines due to the oxidation of ethanol. It is also known as ethanal. It masks fresh fruit aromas and has a stale smell that is regarded as a fault in most wines. However, it is an important component of the distinctive smell of Fino sherry.
- Diacetyl is produced during fermentation and especially malolactic conversion. It contributes a buttery aroma.
- In certain conditions, yeast can produce reductive sulfur compounds during fermentation and lees ageing. Depending on the types of compounds present in the wine and their levels of concentration, aromas can range from struck match, which may be desirable, to rotten eggs, which would be regarded as a fault.
Explain aromas from other sources?
There are numerous other sources of aromas found in different wines. For example:
- vanillin, which gives aromas of vanilla, is just one of the aromatic compounds that can be derived by ageing wine in new oak barrels.
- eucalyptol, which can be volatized from eucalyptus trees by heat and absorbed in the waxy layer of the skins of grapes in nearby vines, may be detected in wine.
The aromas in wines have been the subject of intense scientific research in recent years. This is a complex field due to the sheer number of compounds involved, and especially due to the final aroma of a wine being the product of the interaction between aromatic and non-aromatic compounds in wine. This complexity is summarised in the diagram of Vincente Ferreira’s model for wine aromas.
Explain residual sugar?
Dry wines will usually have a small amount of RS (2–3 g/l), while off-dry to sweet wines will have much more (Sauternes can have 150 g/l, Pedro Ximenez sherry can have up to 400 g/l). In addition to contributing a level of sweetness to wines, RS gives more body to them.
Explain the EU classification of sweetness levels?
The EU has two classifications of sweetness levels in wine. The one for sparkling wines is covered in the unit on that topic. The classification for still wines is reproduced here. These terms do not have to appear on labels, although some regions (e.g. Alsace) are encouraging their use or bespoke sweetness codes in order to guide customers.
The classification takes into account two factors – levels of residual sugar and optionally higher levels of RS for wine with higher total acidity – in an attempt to guide consumers as to the taste of the final wine.
Dry/sec/trocken, etc. – up to 4 g/l RS, or not exceeding 9 g/l provided that total acidity expressed as grams of tartaric acid per litre is not more than 2 g below RS content. For example, a wine with 9 g/l RS can be labelled ‘Sec’ if it has 7 g/l total acidity.
Medium dry/demi-sec/halbtrocken, etc. – more than 4 g/l and not more than 12 g/l RS, or up to 18 g/l provided that the total acidity expressed as grams of tartaric acid per litre is not more than 10 g below the RS content.
Medium or medium sweet/moelleux/lieblich, etc. – more than 12 g/l and not exceeding 45 g/l RS.
Sweet/doux/süss etc – at least 45 g/l RS.
Explain glycerol?
Glycerol is the most abundant part of wine after water and alcohol (in dry wines) and is derived from the sugar in grapes. It occurs in higher levels in wines made from botrytis-affected grapes (e.g. Tokaji) and wines made by carbonic maceration (e.g. basic Beaujolais) although to a lesser extent than those made from botrytis-affected grapes.
Glycerol contributes smoothness to the texture of wine and the perception of the fullness of the body. It has a slightly sweet taste.
Explain phenolics?
Phenolics refers to an important group of compounds that occurs in grapes, especially in the skins, stems and seeds. They include both anthocyanins (colour pigments responsible for the red colour – and sometimes blue tints – of red and rosé wines) and tannins.
In broad terms, tannins bind with proteins in the mouth, giving a drying sensation on the palate. However, the exact relationship between the tannin compounds in the grapes, tannin compounds in the wine and the sensation of tannins in the wine is very complex and not well understood. It is thought that the perception of tannins can be influenced by the other compounds in the wine. A little residual sugar can make tannins seem softer, whereas dry wines with high acidity can make tannins appear more astringent.
Tannins can also react with other compounds in wine during winemaking and maturation, changing their composition and hence how they are perceived. Unripe tannins generally taste bitter and are never desirable. The level and nature of the tannins and their role in the balance and structure of the wine as a whole is considered a key part of quality in red wines.
