INFLUENCE OF URONIC-ACIDS ON THE SPONTANEOUS PRECIPITATION OF CALCIUML-(-TARTRATE IN A MODEL WINE SOLUTION())

Polygalacturonic acid has been found to inhibit the spontaneous precip itation of calcium tartrate in a model wine solution. The monouronic a cids, galacturonic and glucuronic, do not affect the crystallization o f calcium tartrate. Using a calcium ion selective electrode, the bindi ng of calcium to polygalacturonic acid was found to reach a maximum at pH 4 with significant complexation occurring between pH 3.0 and 3.5. The polygalacturonic acid also affects the membrane asymmetry potentia l of the calcium ion selective electrode, and an appropriate correctio n must be applied. A study of the concentration of polyuronic acids (c hain length >8) in commercial wines by the m-hydroxybiphenyl method sh owed that they are present at sufficient concentration to inhibit the calcium tartrate precipitation in wine. Sparkling wines have a much lo wer concentration of polyuronic acids than still white table wines, an d this difference may be responsible for the calcium tartrate stabilit y of white table wines.