**2. High hydrostatic pressure (HHP)**

HHP was developed at an industrial scale in the last century by Gec Alston Company in Europe, even when their basis and initial prototypes where defined by Hite in 1899 [41]. Technological difficulties delayed the production of industrial devices able to work at industrial scale until the 80s of XX century. HHP technique uses the hydrostatic pressure transmitted by a liquid, usually water, to pressurize a liquid or solid food in order to eliminate microorganisms or modify some food properties (**Figure 2**). In HHP systems, the pressures are applied by a liquid and therefore homogeneous pressurization is produced on the whole surface of the food. The low-pressure pump is used to quickly fill the vessel with water. It is important to reach a high filling ratio to reduce the volume of water necessary and therefore decrease the dead-times. When air is removed and the vessel is completely filled with water, the secondary high pressure pump is used to continue introducing water to increase the pressure. It is normally necessary to introduce an additional 4% volume of water to reach the working pressures of 400–600 MPa needed to eliminate the microorganisms.

Typical pressure ranges to eliminate microorganisms by HHP are 300–400 MPa for yeasts and molds, 400 MPa for Gram-negative bacteria, and 500–600 MPa for Gram-positive during processing times of 3–10 min [42]. Sporulated bacteria cannot be controlled by HHP because pressures around 1000 MPa are needed, which is not feasible for industrial equipment. The application of 200 MPa for 10 min on the grapes can decrease the indigenous yeast populations, with 400 MPa often being enough to eliminate the yeasts from the grapes [5, 6]. However, even the treatment of 550 MPa for 10 min may not be able to completely eliminate bacterial populations [5]. The elimination of indigenous yeasts facilitates the implantation of inoculated non-*Saccharomyces* yeasts and the better expression of their metabolic activities [6]. Furthermore, the elimination of both wild yeasts and bacteria helps to reduce the levels of sulfites needed for their control.

HHP can be considered a non-thermal technology because the adiabatic compression heat is around 2–3°C/100 MPa, so pressurization at 500 MPa increases

#### **Figure 2.**

*High hydrostatic pressure system. The pressure vessel is filled with water by means of a low-pressure, high flow rate pump and then increased to working pressure by an intensifier.*

**31**

**Figure 3.**

*for 10 min.*

*Emerging Technologies to Increase Extraction, Control Microorganisms, and Reduce SO2*

the temperature by only 10–15°C. In addition, heat exchangers are incorporated in the pressurization vessel to either refrigerate or to apply thermo-pressurization. Moreover, pressure forces are unable to modify covalent bonds, so most of the molecules responsible for sensory properties (pigments, aromas and flavor substances) remain unaffected during HHP processing. Therefore, HHP can be considered a gentle technique in terms of preserving sensory quality. Moreover, even when grapes are pressurized with intense treatments (500–600 MPa), no heat treatment markers such as Maillard compounds are observed in the HHP-

The antimicrobial effect of pressure mainly affects the microbial envelopes: cell wall, cell membrane, and nuclear membrane in yeasts. When microorganisms are pressurized and subsequently returned to atmospheric pressure, all these microbial structures are affected by the poration or completely broken, making the cells nonviable. At the same time, foods are unaffected or slightly affected by their texture and appearance. The pressure only produces a homogeneous volume reduction that can be quantified as 4% and the external appearance of the grapes remains unal-

The external aspect does not show the effect of the HHP processing but on a molecular scale both membranes and cell wall are altered, causing the migration of pigments and phenols from the grape skin to the pulp (**Figure 4**). Even anthocyanin staining of seeds is observed after HHP treatment [5]. This migration of phenolic compounds produces a faster extraction of these molecules and probably of the aromatic precursors from the skins to the pulp, facilitating grape maceration. Anthocyanin extraction may increase by 20–80% in HHP-processed grapes compared to controls [4, 5], and the wines produced have a significantly higher color

HHP processing can be used as a gentle technique to control microorganisms in grapes, thus facilitating the implantation of inoculated starters, especially when they have weaker performance than *S. cerevisiae*. In addition, the intense effect on cell walls helps to increase extraction by reducing conventional maceration times in

Currently, industrial devices equipped with horizontal vessels of 55–525 L are available for HHP, able to work up to 600 MPa, and to process up to 3000 kg/h [27]. To reduce dead-times, HHP machines are equipped with a high number of intensifiers: 4–16 depending on the vessel capacity [27, 43]. The most important companies

*External appearance of* Vitis vinifera *L. cv. Tempranillo grapes processed by HHP at 200, 400, and 550 MPa* 

*DOI: http://dx.doi.org/10.5772/intechopen.92035*

tered even at pressures of 550 MPa (**Figure 3**).

in HHP technology are Hiperbaric [27] and Avure [43].

intensity and tannin content [5].

red winemaking [3].

processed musts.

## *Emerging Technologies to Increase Extraction, Control Microorganisms, and Reduce SO2 DOI: http://dx.doi.org/10.5772/intechopen.92035*

the temperature by only 10–15°C. In addition, heat exchangers are incorporated in the pressurization vessel to either refrigerate or to apply thermo-pressurization. Moreover, pressure forces are unable to modify covalent bonds, so most of the molecules responsible for sensory properties (pigments, aromas and flavor substances) remain unaffected during HHP processing. Therefore, HHP can be considered a gentle technique in terms of preserving sensory quality. Moreover, even when grapes are pressurized with intense treatments (500–600 MPa), no heat treatment markers such as Maillard compounds are observed in the HHPprocessed musts.

The antimicrobial effect of pressure mainly affects the microbial envelopes: cell wall, cell membrane, and nuclear membrane in yeasts. When microorganisms are pressurized and subsequently returned to atmospheric pressure, all these microbial structures are affected by the poration or completely broken, making the cells nonviable. At the same time, foods are unaffected or slightly affected by their texture and appearance. The pressure only produces a homogeneous volume reduction that can be quantified as 4% and the external appearance of the grapes remains unaltered even at pressures of 550 MPa (**Figure 3**).

The external aspect does not show the effect of the HHP processing but on a molecular scale both membranes and cell wall are altered, causing the migration of pigments and phenols from the grape skin to the pulp (**Figure 4**). Even anthocyanin staining of seeds is observed after HHP treatment [5]. This migration of phenolic compounds produces a faster extraction of these molecules and probably of the aromatic precursors from the skins to the pulp, facilitating grape maceration. Anthocyanin extraction may increase by 20–80% in HHP-processed grapes compared to controls [4, 5], and the wines produced have a significantly higher color intensity and tannin content [5].

HHP processing can be used as a gentle technique to control microorganisms in grapes, thus facilitating the implantation of inoculated starters, especially when they have weaker performance than *S. cerevisiae*. In addition, the intense effect on cell walls helps to increase extraction by reducing conventional maceration times in red winemaking [3].

Currently, industrial devices equipped with horizontal vessels of 55–525 L are available for HHP, able to work up to 600 MPa, and to process up to 3000 kg/h [27]. To reduce dead-times, HHP machines are equipped with a high number of intensifiers: 4–16 depending on the vessel capacity [27, 43]. The most important companies in HHP technology are Hiperbaric [27] and Avure [43].

**Figure 3.**

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

from the grapes [2, 6, 8, 14, 16, 21].

**2. High hydrostatic pressure (HHP)**

levels of sulfites needed for their control.

*rate pump and then increased to working pressure by an intensifier.*

activities. Most non-*Saccharomyces* usually have lower fermentative power than *S. cerevisiae* or slower fermentation kinetics (e.g., Sp), which reduces the possibilities of being well implanted [40]. New emerging non-thermal technologies facilitate the use of non-*Saccharomyces* yeasts by eliminating or strongly reducing wild yeasts

HHP was developed at an industrial scale in the last century by Gec Alston Company in Europe, even when their basis and initial prototypes where defined by Hite in 1899 [41]. Technological difficulties delayed the production of industrial devices able to work at industrial scale until the 80s of XX century. HHP technique uses the hydrostatic pressure transmitted by a liquid, usually water, to pressurize a liquid or solid food in order to eliminate microorganisms or modify some food properties (**Figure 2**). In HHP systems, the pressures are applied by a liquid and therefore homogeneous pressurization is produced on the whole surface of the food. The low-pressure pump is used to quickly fill the vessel with water. It is important to reach a high filling ratio to reduce the volume of water necessary and therefore decrease the dead-times. When air is removed and the vessel is completely filled with water, the secondary high pressure pump is used to continue introducing water to increase the pressure. It is normally necessary to introduce an additional 4% volume of water to reach the work-

ing pressures of 400–600 MPa needed to eliminate the microorganisms.

Typical pressure ranges to eliminate microorganisms by HHP are 300–400 MPa for yeasts and molds, 400 MPa for Gram-negative bacteria, and 500–600 MPa for Gram-positive during processing times of 3–10 min [42]. Sporulated bacteria cannot be controlled by HHP because pressures around 1000 MPa are needed, which is not feasible for industrial equipment. The application of 200 MPa for 10 min on the grapes can decrease the indigenous yeast populations, with 400 MPa often being enough to eliminate the yeasts from the grapes [5, 6]. However, even the treatment of 550 MPa for 10 min may not be able to completely eliminate bacterial populations [5]. The elimination of indigenous yeasts facilitates the implantation of inoculated non-*Saccharomyces* yeasts and the better expression of their metabolic activities [6]. Furthermore, the elimination of both wild yeasts and bacteria helps to reduce the

HHP can be considered a non-thermal technology because the adiabatic compression heat is around 2–3°C/100 MPa, so pressurization at 500 MPa increases

*High hydrostatic pressure system. The pressure vessel is filled with water by means of a low-pressure, high flow* 

**30**

**Figure 2.**

*External appearance of* Vitis vinifera *L. cv. Tempranillo grapes processed by HHP at 200, 400, and 550 MPa for 10 min.*

#### **Figure 4.**

*Color of the grape juice extracted without maceration: unprocessed (control) or pressurized at 550 MPa for 10 min.*
