AcidityDifferent acidities of wine. In the mouth it is felt on the sides of the tongue, but the acidity which one finds in a wine is the result of a group of acidic substances, some from the grape and others from the fermentation process. These are fundamental to the balance of the wine, not merely from the point of view of taste but also to help it keep over time. In brief, the acidity is the fuel which allows the wine to go a long way.
The total acidity of a wine includes all the volatile substances as well as the fixed substances. It is much more useful to refer to the pH of a wine, which expresses the real acidity of a substance, giving its real level. The pH is measured on a scale of 0 to 14 and the lower the figure the higher the acidity.
The pH figure, then, will be lower in fresh, fragrant wines where the grapes were harvested early to keep a high level of acidity. In more important, long-lived wines the pH will be higher (so the acidity will be lower) but should be well balanced and in harmony with the structure of the wine.
For these wines it is important that the acid substances are less aggressive: this is why the alcoholic fermentation is followed by a malolactic fermentation which changes the malic acid into lactic acid, which is weaker and gives the wine more smoothness.
Ageing and maturingNot all grape varieties and not all grapes have the broad backs they need to be able to age over time. The choice, then, is first made out in the countryside, by deciding which type of wine the grapes are going to be used for. Young wines can be drunk from the spring after the grape harvest onwards. There are wines which only rest a few months after the alcoholic fermentation before being bottled.
The more important wines must start from sound grapes with a good balance of sugars and acidity, able to take the wine to its peak. There are wines which, after alcoholic fermentation and malolactic fermentation, are allowed to rest for a period (which may be longer or shorter) in wooden barrels (small barrels or large ones). This is a period when the wine acquires complexity as new aromas form.
This is followed by a long period in the bottle, where the wine undergoes further slow changes until it reaches the highest point of its development in terms of colour, elegance, development of its bouquet, structure, smoothness and roundness.
Ageing in wood and long bottle-ageing are usually for red wines (with a greater variety of substances), but sometimes they are also suitable for certain white wines which are to be kept for a long time.
Alcoholic fermentationThis is the first stage of winemaking, a complex biochemical phenomenon which involves transforming the sugars (glucose and fructose) into ethyl alcohol (ethanol), carbon dioxide and numerous products which are known as secondary products because they are present only in small quantities.
The agents for this process are the yeasts in the grapes which feed on the sugars and change them. During alcoholic fermentation heat is also produced, but the process may stop if the temperature reaches 35°-38°C; in this situation the must becomes vulnerable to bacteria which change the sugars into mannitol, producing an undrinkable liquid.
In order to prevent this danger (mannitolic fermentation) the cellar must be aired and cold water has to be run over the fermentation vessel. Other measures maybe adopted, depending on the situation in the place concerned. The most up-to-date vessels have a double skin with an internal cavity where a cooling or heating liquid circulates, thereby allowing the temperature of the process to be controlled. In northern areas there may be the opposite risk; fermentation may not start because the temperature is too low (10°C). In this case the cellar and the must would obviously have to be heated.
The start of alcoholic fermentation is signalled by gurgling caused by carbon dioxide gas being given off. Due to this typical noise fermentation is known in the trade as boiling.
Alcoholic strengthIt has been proven that alcohol in moderate doses has beneficial effects on health. The alcohol in wine is ethyl alcohol, the result of the transformation of sugars due to the action of yeasts in the grapes. It follows that a grape with a higher sugar content will give a higher level of alcohol. This is measured in millilitres at 20°C and may be defined as the alcohol percentage by volume. To give a practical example, when a wine is labelled as 11° this means that it contains 11% alcohol by volume (or 110 millilitres of alcohol per litre of wine), one of 12° contains 12% of alcohol and so on. By law table wines have to contain at least 8% (or 9° of alcohol). In certain cases the label may state 'potential degree of alcohol'; these are usually sweet wines which still contain sugars which, at least in theory, could ferment and make more alcohol; this is the potential degree of alcohol.
Alcohol is one of the elements which has the biggest effect on the quality of wine. It is the main factor responsible for the smoothness, mellowness and roundness and it contrasts with and masks the effects of acidity and astringency, acts as a support for the primary aromas and plays a key role in the various process the wine undergoes during development. This is why it is very important to have a reasonable level of alcohol even if it has to be corrected during alcoholic fermentation.
Italian law allows the alcoholic level to be corrected by a maximum of two units. This practice is not common among the more careful winemakers who pay the greatest possible attention to raising the sugar level in the grapes on the vine and not intervening later. In Italy the most common system is addition of concentrated rectified must, a colourless, odourless sugary solution obtained by removing the water from grape must - a sugar concentrate in practice.
In France, and also in other countries, sugaring is allowed; the practice of adding sugar to feed the yeasts which will make it into more alcohol. In Italy the sugar level can only be increased, under strict controls, in fortified or strong sweet wines and in aromatized wines.
AmpelographyA small to medium-sized leaf, three and five-lobed, with a lyre-shaped stalk cavity with overlapping borders. The mature bunch of grapes is medium-sized, compact, conical-cylindrical, sometimes pyramidal.
The grape is medium-sized, with a persistent stylar remnant, golden yellow in colour, tending to amber…
We shall stop here but we could continue for many pages. This is a fragment of a detailed description of a variety of vine, an identity card which describes it in minute detail.
The vine description scheme is the final product of ampelography, a science which deals with the classification and description of the different species and varieties of vine. This is not an easy task; Vitis vinifera is a plant which adapts to life in very different soils and climates, by continued mutation.
The most common descriptive scheme is the one approved by the international commission of the Office International de la Vigne et du Vin (O.I.V.) are for each variety of vine it gives the name, common names, vegetative characteristics (habit, vigour, description of the bunch of grapes, the grape, the leaf, how long it takes to germinate, when it matures), how it responds to cultivation (behaviour with regard to climatic factors, insects and diseases) and the most suitable habitats.
The sample of text, by the way, comes from an ampelographic description of Muscat.