4. Refrigeration requirements for the chemical stabilization of wines

Freshly fermented wine is a saturated solution of tartaric salts whose solubility depends on the alcoholic strength and temperature. In order to avoid the presence of soaps once the wine is bottled, it is necessary to produce in the winery the insolubility and subsequent precipitation of these tartaric salts, mainly potassium bitartrate and calcium tartrate. For this, the wine is subjected to low temperatures modifying its solubility. This must refrigeration presents other side effects of great importance: precipitation of coloring matter and unstable proteins, insolubilization of colloids and reduction of the wine microbial load and facilitates the subsequent process of microbiological stabilization

According to Boulton [13], Maujean [29] and Moutonet et al. [30, 31], the formation of tartrate crystals follows a kinetic of the form (Eq. (13)):

$$[Tattrates]/t = K\_v \times N \times \left(\mathbb{C}\_d - \mathbb{C}\_s\right)^F \tag{13}$$

Kv is the constant that depends on the concentration in salts of the wine and its temperature.

N is the number of existing crystals per ml of wine.

Ca is the concentration of the existing tartrates.

Cs is the concentration of saturation.

On the other hand, a certain percentage of the energy released in fermentation is dissipated by the environment, depending on the outside temperature. When the set fermentation temperature is lower than the environment temperature, it produces a thermal transfer from the environment to the tank. The calculation of the energy released or absorbed is based on the

U is the heat transfer coefficient. It is a function of the material of constitution of the tank as well as the speed of circulation of the air in the exterior and the presence or not of circulating currents inside the same. According to various authors, the mean value for stainless steel tanks, the static regime of outdoor air and must/indoor wine is U = 16.72 kJ/m<sup>2</sup> H �C [3, 8-10]

ΔT is the temperature difference between the must in fermentation with the exterior (�C or �K). If fermentation tank (or later of storage) is located outside the winery, the solar thermal input is important in regions with high isolation. In order to calculate the energy input, it is necessary to take into account the degree of incidence of the solar rays on the surface of the deposit. Flanzy [3] considers that this thermal contribution varies between 400 w/m2 in winter and 800 w/m2 in summer for northern countries. Generally speaking, in Spain, the values can vary between

the fermentation mas takes place. In complex calculations, involving many variables not always known, this heat dissipation is not taken into account when calculating the cold storage

According to what has been said so far, the heat produced during the fermentation process to

Freshly fermented wine is a saturated solution of tartaric salts whose solubility depends on the alcoholic strength and temperature. In order to avoid the presence of soaps once the wine is bottled, it is necessary to produce in the winery the insolubility and subsequent precipitation of these tartaric salts, mainly potassium bitartrate and calcium tartrate. For this, the wine is subjected to low temperatures modifying its solubility. This must refrigeration presents other side effects of great importance: precipitation of coloring matter and unstable proteins, insolubilization of colloids and reduction of the wine microbial load and facilitates the subsequent

According to Boulton [13], Maujean [29] and Moutonet et al. [30, 31], the formation of tartrate

4. Refrigeration requirements for the chemical stabilization of wines

, respectively. On the other hand, during the night, a significant cooling of

Qtotal ¼ Qf ermentation–Qdissipated by CO2, H2O and ethanol � Qambient (12)

Q ¼ U � S � ΔT (11)

conduction/convection heat transfer equations (Eq. (11)) [8–10]:

S is the outer surface of the tank in contact with the environment.

needs, being a margin of safety of the calculations made.

be dissipated by the application of cold is (Eq. (12)):

process of microbiological stabilization

crystals follows a kinetic of the form (Eq. (13)):

or U = 4.64 w/m2

82 Refrigeration

700 and 1100 w/m<sup>2</sup>

.

�K [3, 18].

F is the conversion factor. It ranges between 5 and 7.

The tartaric stabilization can be carried out discontinuously and continuously. The traditional or continuous stabilization is based on cooling the wine to a temperature close to the freezing temperature set in

$$\text{Ta} = \frac{\text{alcohol} \text{circ} \text{degree } -1}{2},$$

which means reaching temperatures of �5/�6�C. Once the wine has been cooled at this temperature, it is stored in isothermal tanks and they remain until Tsat control data, conductivity or other stability tests result in the stabilization of the wine [2, 18, 32]. This guard time lasts between 7 and 10 days. The modern stabilization systems, continuous or semicontinuous, are based on the refrigeration of the wine to a temperature close to 0�C or slightly lower (�2.5�C) with addition of microcrystals of tartrates in variable concentration (generally 4 g/L) and continuous stirring contact method. With these procedures, the treatment time is reduced from 7–10 days to 60–90 min [12, 33]. In both cases after the treatment, the wine already treated gives its cooling energy to the wine that enters by a plate exchanger. Subsequently, it is subjected to a process of filtration by earth or plates to eliminate crystals.

The refrigeration capacity required to cool the wine until the stabilization temperature of �5/�6�C (batch system) to �2.5/0�C (continuous system) is defined by the expression (Eq. (14)) [3, 8–10]:

$$\mathbf{dQ}/\mathbf{d}t = m \times \mathbb{C}\_{\epsilon} \times Dt \tag{14}$$

dQ/dt is the cooling capacity per unit of time (kJ/h).

m is the mass flow of wine (kg/h). m = v x r.

v is the volumetric flow rate (m3 /h).

r is the density (kg/m3 ).

Ce is the specific heat of the wine that according to author is Ce = 3.99 kJ/kg �C [16]; Ce = 4.18 kJ/kg �C [3, 20]; Ce = 4.5 kJ/kg�C [10].

Dt is the (initial temperature–final temperature) of the wine.
