Lowering Wine Acidity with Carbonates

Abstract

Prior to deacidification, titration curves for three highly acid wines were obtained. A prominent feature of each titration curve (and of those of malic and tartaric acids) is a prolonged linear segment extending to pH of 5. This feature is directly related to the total concentration of tartrate plus malate plus other buffers present. The buffers must often be removed in order to lower acid while maintaining pH at reasonable levels for stable wine. Carbonate was used to neutralize the acidity of wine with the cation of the carbonate (K⁺ or Ca⁺⁺) serving to precipitate tartrate. Ca⁺⁺ serves also to precipitate malate, but to a much smaller extent.

Three wines treated with KHCO₃ are evaluated in terms of the recently proposed acidity index (Total acid — pH). The index shows that the use of KHCO₃ will not suffice to deacidify wines in which the pH is high relative to total buffers and total acid. For practical purposes, the pH must be below 3.0 if the titratable acid is above 10 g/L for KHCO₃ treatment to be effective. A more general relationship between pH and buffer capacity is presented.

For CaCO₃ treatment, the slurry, or "double salt", method is compared with a number of direct methods for CaCO₃ addition. Although the direct methods may equal or even surpass the slurry method in terms of amount of malate removed, the slurry method does not result in as high a residual Ca concentration. All CaCO₃ methods leave Ca concentrations high enough to be tasted in water and fail to precipitate most of the malate. Consequently, it is suggested that for wines having malate much in excess of 4 g/L, malo-lactic fermentation may be the preferred method for deacidification.