Cold stabilisation is used to remove excess tartaric potassium bitartrate acid. The process of cold stabilisation chills the wine down to about —4 to 0°C (25-32°F). The KHT acid crystallizes and is drawn off by racking. This can take several days or may be sped up through the addition of fine ground cream of tartar seed crystals. The contact process allows stabilisation to be accomplished in a continuous manner in 4 h with heat recovery between input and output streams. Karousou et al.’s [17] study calculated that 0.029 kWh of cooling is necessary per litre of red and white wine for cold tartaric stabilisation using glycol cooling at — 10°C.
In a study by Dugger [11], the merits of insulation for tanks during cold stabilisation are presented. In the study, two white wines were traditionally glycol cooled in a tank with and without insulation and the energy intensities compared. The uninsulated tank required 0.317 kWh/l whilst the insulated tank required only 0.006 kWh/l. In the same study a comparison was made between traditional glycol cooled tanks against flash refrigeration techniques. Flash refrigeration or freezing is a process whereby the substance is subjected to cryogenic temperatures using liquid nitrogen or a mixture of dry ice and ethanol. In their study, the red wine getting cooled in the traditional tank, with no insulation, required 0.2 kWh/l, whilst the flash refrigerated red wine in the other tank only required 0.012 kWh/l.
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Cold stabilisation through the crystal flow process is very energy intensive. Another method to remove excess bitartrate acid that has been investigated is electro-dialysis. Electro-dialysis is a membrane process driven by an electric current, moving the tartrate ions from the wine through a membrane to an aqueous solution. This technology was developed in Europe and is applied in wineries around the world. In trials, energy intensities of less than 8 kWh/US gallon have been recorded for both reds and whites [13]. On the downside there are issues relating to space, time and winemaking style, in addition to increased water consumption leading to increased wastewater treatment and associated energy costs. Moisture in the air surrounding the tanks results in surface condensation on the tanks and due to the very low flow temperatures, ice forms (Fig. 4.170). This change of state absorbs significant energy, changes the heat transfer characteristics, leading to an increase in the refrigeration load. The legalisation of bitartartate crystallisation inhibitors such as metatartaric acid or more notably CMC, offers an alternative to this energy intensive step.
