Wine Components Flashcards
Name the principal acids of wine that naturally occur in the grape and two acids that can occur from fermentation or MLC?
Tartaric and Malic acid occur naturally in the grape and generally make up about two thirds of the total acidity in wine.
Lactic and acetic acid.
Explain volatile acidity?
olatile 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.
What does acidity contribute to wine?
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.
What does a low pH do in wine?
A low pH increases the microbiological stability of wine, increases the effectiveness of SO2, gives red wines a bright red colour (Anthocyanins are more stable at low pH (acidic conditions) which gives a red pigment.) and enhances a wine’s ability to age well.
What are examples of aromatic compounds that are found in the grapes?
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.
What are two categories of aroma precursors?
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 an Ester and its contribution to wine aroma.
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. Responsible for many fresh and fruity aromas, therefore essential in the aroma profiles of young wines. The most common ester is Isoamyl Acetate, responsible for banana aroma in Beaujolais Nouveau. Most esters are unstable and will breakdown a few months after fermentation
Explain Acetaldehyde and its contribution to wine aroma.
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.
Explain Diacetyl and its contribution to wine aroma.
Diacetyl is produced during fermentation and especially malolactic conversion. It contributes a buttery aroma.
Explain reduction and its effect on wine 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 Glycerol and its effect on wine.
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 and its effect on wine.
Phenolics refers to an important group of compounds that occurs in grapes, especially in the skins, stems and seeds. Includes 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.
