History of Wine - Production and elaboration
Man has been continuously incorporating new technologies to winemaking as his understanding of the process has become more sophisticated. It has been discovered that wine must be made in an oxygen-free environment to prevent it from spoiling. Grape harvesting is a very delicate procedure, since it must be done quickly to guarantee the quality of the wine.
Pressed/crushed
In the past, grapes were pressed immediately after the harvest to obtain the must (Vitis vinifera juice). It was normal to see people without shoes stepping on grape yields in compartments with a perforated bottom, thus obtaining the initial must. In his book De Agri Cultura, Catón explains the pressing procedure in detail. This method was suitable for small-scale production; later screw presses arrived, which allowed pressure to be regulated. Nowadays, hermetic pneumatic presses are used in which the delicacy of pressing allows the extraction of fewer unwanted substances and the maximum respect for the intrinsic qualities of the grape. As a rule, grapes are pre-cleaned by removing vegetation and scrapes (stalks from clusters).
This process is completed in perforated metal drums that rotate at high speed and the grapes come out whole through the holes in the drum. It is essential that most of them remain intact to prevent their inner juice from coming into contact with the atmosphere.
Crushing is usually the standard technique used in white wines to avoid removing anthocyanins from the skins. Pressing is more typical of red wines. When crushed, the grapes do not turn into puree, which allows the juice to be extracted from the mesocarp and endocarp of the grape. Highly concentrated grape musts are used in some wines, such as marsala, mistela, Malaga wine and others.
Fermentation
Fermentation is an integral part of winemaking, since it is impossible to create wine without it. This process occurs when the sugars in the must are converted into ethyl alcohol by yeasts of the genus Saccharomyces. The two most common species are S. cerevisiae and S. bayanus, which are used for Sherry wine, but there are other subspecies such as Montrachet, Epernay and Steinberger that have been artificially selected for various qualities such as pH levels, alcohol content and sulfur dioxide (SO2). Fermentation takes place in special tanks (currently they are usually made of stainless steel) and consists of four stages.
1. During the dormancy phase, yeasts get used to the characteristics of the must, such as the high concentration of sugar, the low pH level, the temperature and the level of sulfites. This process usually takes two to three days to complete.
2. Exponential growth: When yeasts are already acclimated to the environment, the multiplication of their population increases dramatically, generally reaching a maximum of about one hundred million cells per cubic centimeter. However, since yeasts quickly consume the sugar in the wort, the amount of yeasts present is rapidly reduced. This phase lasts about four days.
3. During the stationary phase, the yeast has reached its maximum population level, which leads to a steady state and to the fermentation rate remaining unchanged. In addition, the heat generated by fermentation maintains the same temperature in the fermentation vessel.
4. During the deterioration phase, yeast cells begin to die due to the absence of sugar or the large amount of alcohol, which causes a decrease in the number of yeasts and, consequently, the rate of fermentation is reduced.
It is believed that several modern winemaking techniques, such as the inoculation of yeasts during the stationary phases to reach the maximum of 108/ml, increase the complexity of wine flavors. This practice is widespread in vineyards in France and California. However, some winemakers prefer to use wild yeasts that are already present in the fermentation environment, which has sparked debate. To measure the progress of fermentation, a pycnometer is used to measure the density of the liquid sample from the tank. The density of must is higher than that of wine, which allows two limits to be established to control the fermentation process.