**4. Technologies to increase the extraction of anthocyanins and the wine color**

As stated before, an essential step in the red winemaking process is the extraction of the colored compounds, along with tannins and aromatic molecules, from skins to the must during maceration. This means that it is necessary to keep skins and seeds in contact with the must in the tank during fermentation to extract and diffuse these phenolic compounds in the must and to obtain the end color of the wine and this extraction will be affected by several technological factors such as fermentation temperature, cap management, SO2, ethanol content. There are several techniques that may favor the extraction and increase de concentration of anthocyanins in musts and wine, assuring enough substrate for long-term highly colored wines.

Cold maceration: The extraction kinetics can also be improved with enological techniques such as the use of cold soak (cold maceration), dry ice, or enzymes affecting the extraction of anthocyanins and proanthocyanidins. Cold soak is based on the use of low maceration temperatures, 4–15°C [62]. It applies refrigeration to the must in order to delay the beginning of fermentation and that means that maceration is done with the absence of ethanol, so extraction of anthocyanins is more favored than tannin extraction.

Enzymes: They are a commercial mixture of different enzymes with different pectolytic activities, mainly endo-polygalacturonase, pectin-methyl esterase and pectin-lyase activities, that are added to the crushed grapes with the purpose is to disassemble the cell wall structure, thus facilitating extraction of the compounds located inside the grape cells [63]. These enzymes have been shown to have a positive effect in several studies [64–66].

The use of high temperatures (thermovinification): Although generally heating of the grapes before fermentation is called "thermovinification", different pre-fermentation heating processes are currently being applied in wineries. These techniques can be classified into two groups, depending on whether the cooling of the grapes,

similarly to heating, is conducted using heat exchangers, or whether the cooling is conducted into a vacuum chamber.

The first kind of process is designated as "thermovinification". The second group involves the technique called thermo-flash, flash détente or flash-release [67].

During thermovinification the grape mash is heated up to 85°C, and both heating and cooling are conducted in heat exchangers [68]. Heating is conducted for a period of time of less than one hour, after which the grape mash is pressed to separate the solid parts and perform fermentation as for white wine. If heating at the same temperature is extended for a longer period of time (up to 24 h), and the fermentation is conducted in the presence or absence of the solid phase, the process is called pre-fermentation hot maceration.

The process called "flash release" or "flash détente" consists in rapidly heating the grapes at temperatures between 85–95°C by a direct injection of steam. Grapes are then introduced into a vacuum that instantly vaporizes the water, thereby cooling the treated grapes and weakening their skin cell envelopes by boiling the water inside the cells [69, 70]. This effect on the skin cells enhances extractability in subsequent fermentation process that may be conducted with or without the solid parts of the grapes. Flash technology differs from traditional thermo-vinification because the traditional method does not involve a vacuum and there is no flash water waste produced.

Emerging technologies: There are other emerging technologies such as high hydrostatic pressure (HHP), pulsed electric fields (PEFs), ultrasounds (USs), irradiation, pulsed light (PL), ozone and electrolyzed water are opening up new possibilities in wine technology. Among them, US and PEF are already used technologies and they can improve the extraction of anthocyanins from skins to must.

Pulsed Electric Fields: PEFs increase the rate and yield in the extraction of phenolic compounds in red grape processing [71]. PEF processing consists in the intermittent application of short duration pulses (ms-s) of high voltage (kV) to the crushed grapes located between two electrodes. The applied external voltage generates an electric field whose strength depends not only on voltage intensity, but also on the distance between the electrodes. When exposed to a sufficiently strong electric field, the cell membrane undergoes a phenomenon called electroporation, consisting in the increment of cell envelope permeability as a consequence of the formation of pores in the cytoplasmatic membrane [72]. By using PEFs, the extraction of total phenolic compounds can be increased by 10–50% [73] and maceration time can be reduced by 40–50% using PEF intensities of 5–10 kV/cm [74]. Under these conditions, the temperature increment is very low, so it can be considered a nonthermal technology.

Ultrasounds: USs are sonic waves in the range of 20–100 kHz producing cavitation, which is the formation of gas bubbles that are expanded and compressed according to the variation of the wave intensity. Through this phenomenon, local pressure can reach values of 50 MPa and temperatures at specific points can also exceed 1000°C [75]. USs help to destroy cell walls of skins, facilitating the extraction of phenolic compounds. This technology can be used in enology to carry out a fast and continuous extraction, extremely reducing maceration times, and the extracted juice can later be fermented at low temperature in the absence of solids (skins and seeds). The best extraction results can be obtained at low frequencies (30 kHz) inside the USs range. Using this technology, it is possible to reduce maceration time from 7 to 2–3 days with the same degree of extraction in terms of tannins and pigments [76].

The emergence of non-thermal technologies can lead to high quality products while saving energy. Most of these technologies are locally clean processes and

*Anthocyanins and Wine Color: A Complex Story DOI: http://dx.doi.org/10.5772/intechopen.105162*

therefore appear to be more environment-friendly, with less environmental impact than traditional ones.

As a conclusion, the importance of anthocyanins and their reactivity in must and wines has been reviewed, indicating the importance of color in wine appreciation and how these reactions are paramount for a long-term wine color stability.
