HOW RED WINE VINIFICATION TAKES PLACE
A biochemical process of transforming grapes into wine, vinification differs depending on whether white or red wine is the desired result.
More specifically, red wine vinification (or vinification with maceration) involves bringing the pomace and the fermenting must into contact – the solid parts of the grape, i.e. its skin and pips, are placed in contact with the liquid fraction during fermentation so that part of the substances they contain may be extracted.
What distinguishes it from white wine vinification is simultaneous fermentation and maceration.
Alcoholic fermentation of the grapes
It all starts with the harvest, i.e. picking the grapes when they are ripe – the sugar content is at its highest, the acid level at its lowest, and the herbaceous aromas have disappeared. In order to obtain a good red wine, it is essential to harvest the grapes at just the right phenolic and technological maturity, testing these parameters using sensory analyses of the skin, pulp and pips.
It is equally important to remove damaged grapes before proceeding with the following steps – destemming to separate the grapes from their stalks (which would give the wine a bitter taste and contain a great deal of water) and pressing. With this final preparatory step, the liquid portion emerges from the berry and fermentation and maceration are facilitated.
Red wine fermentation, normally carried out in steel vats, is used to transform the glucose and fructose contained in the must into ethanol, carbon dioxide, heat and other secondary products by means of the action of yeasts. Some cellars choose not to add any, and let the indigenous yeasts naturally present on the grapes and in the cellar “drive” the fermentation process. Others add Active Dry Yeast preparations which reduce the risk of any organoleptic or taste deviations.
THE TEMPERATURE AT WHICH RED WINE SHOULD FERMENT
The ideal temperature for red wine fermentation is 27-30°C – modern machines assist in keeping this temperature constant, thereby promoting the production of a quality wine.
During fermentation, the effect is seen as a boiling mass because of the production of high levels of CO2 – the solid part of the must, i.e. the pips and the skins, are raised to the surface by the carbon dioxide and there they float, forming a “floating cap”. During fermentation, this is repeatedly pressed and pumped up to dissolve the polyphenols, preventing the pomace from acetifying and encouraging colonisation by the yeasts. This process can be carried out by hand in the old-fashioned way or can be delegated to machines with which many cellars are equipped (fermenters or vinifiers).
MACERATION OF THE GRAPES
Red wine vinification is also called vinification with maceration.
Maceration consists of keeping the pomace in contact with the must so that the substances contained in the skin and pulp of the grape are extracted.
Maceration times depend on the wine to be produced – 4-7 days for fresh, fruity wines to be consumed young, 15-20 days for tannin-rich wines destined for prolonged ageing. Anthocyanins reach their peak level of release after 2-5 days. On the other hand, tannin release is progressive, and decelerates after 10-20 days.
Several techniques can be used for maceration. Cold, pre-fermentative maceration, for the production of colourful, fruity wines, involves the addition of dry ice for 5-10 days to the tank where the crushed grapes are placed so that it drops to a temperature of 5°C.
Final hot maceration, on the other hand, is carried out at termination of fermentation, and provides a warming blast to the pomace in contact with the wine, which makes for more full-bodied wines.
RACKING OF THE GRAPES
When the fermentation of the red wine is complete, the skins and pips are separated from the must-wine. This procedure is called racking and is carried out at a specific time based on the product that is required.
Rosé wines require early racking, young red wines require medium levels of racking and red wines for ageing require late racking.
For racking, the wine is aerated with the addition of sulphur dioxide – this stage is carried out following the end of fermentation, when residual sugars reach a threshold of 1-2%. In addition, aerating the wine removes any reduction odours.
BOTTLING OF RED WINE
Bottling of red wine is the final stage in its production, which is preceded by stabilisation.
A typical red wine is stabilised by decanting following analytical and organoleptic examination – the liquid is transferred from one container to another to separate the clear liquid from the lees deposits (yeast remains, bacteria, pesticides, small fragments of skin), performing a variable number of dacanting tasks, which depends on the cellar's rules of conduct. A further step is an air test, which is carried out by leaving a small quantity of wine at a temperature of 20°C for 48 hours to check for any changes in colour or odour.
Bottling red wine consists of filling bottles with wine, inserting a cork and capsule and labelling. The wine is then ready to be stored.
DIFFERENCE BETWEEN RED AND WHITE WINE VINIFICATION
The difference between red and white wine vinification lies in the maceration – in red wine vinification, maceration is always applied, whereas in white wine vinification it is not (with the exception of macerated whites or the popular ‘orange wines’ which undergo extensive maceration, thereby achieving golden and orange tones).
Since maceration is used to obtain a higher tannin content and intense pigments, typical of red wines, the production of white wines does not involve the placing of the pomace in contact with the must.