Red grapes normally reach maturity after the white grapes. Thus the winemaker's schedule divides up naturally into whites first and then reds, relieving pressure in the winery.
In the majority of cases, the grape varieties used to produce red wines have white flesh and red skins. This is a very important factor to remember when considering red winemaking. The production process is similar to that for white wines, except that the destemmed, and sometimes crushed fruit is normally not cooled so radically or pressed, but it is pumped directly into fermentation tanks. A small amount of sulphur is often added to the grapes at destemming. This helps to protect against oxidation and kills some of the undesirable yeast and bacteria that occur naturally on the fruit in the vineyard.
Alcoholic Fermentation and Extraction
The alcoholic fermentation of reds needs to be carried out with the juice in contact with the skins. As soon as a tank is full, we add a selected yeast strain to initiate fermentation. The dried yeast is introduced into the destemmed and crushed grapes after re-hydration. The fermentation can take between 7 to 10 days to complete.
The extraction of colour and of tannin flavours from the skins, is an integral part of the red fermentation process. The problem is to keep the skins in contact with the fermenting juice, since the carbon dioxide produced as a by-product of alcoholic fermentation, makes the skins rise to the top of the tanks. Traditionally, the fermenting juice is drawn off from the bottom of the tanks and pumped back into the tank over the skins to create a 'washing effect'. Experience has shown that the number of times and the timing of this operation is instrumental in determining the intensity of the colour and the quality of the tannin favours in the final wine.
At Carsin, we have also installed two rotating Vinimatics, each holding 150 hectolitres (or 15,000 litres). These horizontally placed cylindrical tanks have built-in motors which turn them on their axis. Many people have noted that they look like Cement trucks! The tanks are turned so as to give the desired rate of extraction of colour and flavour. By rotating the Vinimatics, the liquid at the bottom of the tank is efficiently mixed with the skins and seeds on top, thus the colour, tannins and flavouring substances are gently but efficiently extracted from the grape skins. In the last years we have used the vinimatics less often in the red wine production - partly because in the last few vintages of 2006 and 2007 the grapes were not very ripe and we were afraid to extract too many hard tannins from the skins and the pips of the grapes.
We mainly use traditional red wine fermentation tanks. For these, we use a pump and a hose to take the fermenting wine from the bottom of the tank and spray it over the skins on the top. We call this operation 'pumping-over' and in most instances it is carried out 2 or 3 times a day during the course of the alcoholic fermentation. Some of the red fermenters have elements for both cooling and heating in order to help control the temperatures of the fermentations.
The fermentation temperatures for red wines are normally allowed to rise above those for white wine, to help extract the colour and flavours from the skins and seeds. The ideal temperature range is between 18 and 32 degrees Celsius. The temperature of the fermentation will be cooler at the beginning and will rise to a maximum of 32 towards the end of the process.
The fermentation is monitored by observing the sugar levels. At the end of the alcoholic fermentation, the wine is taken from the bottom of the tank and the skins and seeds are then transferred into the winepress to extract the remaining wine. The pressing process is controlled so as not to extract the hard, vegetal tannin favours that are found in the skins and seeds. This press wine is often kept apart from the free-run wine as it can be vegetal and bitter in taste. The wine is then transferred to an insulated tank, ideally at a temperature of at least 20 degrees Celsius.
Malolactic Fermentation
Red wine making also involves a second fermentation - and sometimes white wine making also. It is called malolactic fermentation which is the process whereby the hard, green flavoured malic acid is converted into softer, more agreeable lactic acid. In most properties in Bordeaux, this fermentation, which is carried out by bacteria, occurs just after alcoholic fermentation. If it does not, then it is done the following spring when the weather starts to become warmer.
There are three types of lactic bacteria which can carry out this process, Lactobacillus, Pediococcus and Leuconostoc oenos. This type of fermentation results in a slight decrease in fruity flavours and an increase in complexity. It causes a reduction in the acid taste and also produces volatile acidity. The types of flavours and the amount of volatile acidity produced, depends on the type of lactic acid bacteria that carries out the fermentation. Therefore many winemakers try to control the bacteria which do the conversion. Of the three types, Leuconostoc oenos is preferred. At the moment much research is being carried out on malolactic fermentation. At Carsin we have used laboratory-cultured bacteria, which ensure a minimum of volatile acidity but lately we have let the malolactic fermentations happen naturally by themselves.
After the malolactic fermentation, the temperature of the wine is cooled down and sulphur dioxide is added. Then, 2 to 3 weeks after the fermentation processes are completed, the wine is transferred into barrels for ageing.
Ageing
All the red wine made at Carsin undergoes ageing in oak barrels. The aim of ageing is to allow the wine to stabilize, and to develop softer tannins and more complex flavours. There is, first, the physical process of settling the solids out of the wine. These include dead yeast and bacteria and even grape particles that have managed to pass through the press.
The second process stabilizes the colour and tannins. These two chemical processes are inter-linked and connected to the amount of oxygen in the wine. We find that as the ageing goes on, the colour of the wines change from a medium crimson to a deeper ruby red. This depends on the grape variety and on the amount of sulphur dioxide that is in the wine during this ageing process. The tannins also evolve. Perhaps they do not decrease in quantity but they polymerize and so change their chemical structure and therefore taste. If the ageing is carried out in oak, then wood tannins are transferred to the wine, changing the tannin levels. Red wine chemistry is very complex.
During ageing, the wines are racked every three to four months. This means that the clear wine, or more accurately, clearer wine, is taken away from the solids that have fallen to the bottom of the vessels. The barriques are then washed and refilled.
During the ageing process, red wine is vulnerable to attack by various types of bacteria and yeast, which more than likely will have detrimental affects on the flavour of the wine. The wine becomes open to such attack when it is over-exposed to oxygen and /or has too little sulphur dioxide. One of the most common problems is the presence of acetic acid bacteria which, when allowed to develop in wine, produce large amounts of volatile acidity or vinegar. Storing red wine away from oxygen, except that which the controlled input that the porous properties of oak will allow, is an absolute must. Because of the natural evaporation of wine, the barrels thus regularly need to be topped up with wine, thus minimizing the surface area directly open to oxygen.
Depending on the vintage at Carsin, the expected period of barrel ageing for red wines is about one year. This gives our wines a good balance of fruit, tannins and complexity of flavours. We mature all our red wines in oak, after which we carry out the final blending process.
The wines are blended in tank and the final clarification is done with egg white just before bottling.
