White wine as the heat accelerates its degradation. There are many other acids in small quantities: citric acid, ascorbic acid, α-ketoglutaric, fumaric acid, galacturonic acid, coumaric acid, etc. Their variable quantity varies the pH of the wort. The must of white wine is generally more acidic than red grape must simply because the grape maturity is less advanced. Vitamin C (or ascorbic acid) is present in the grape and the must up to 50 milligrams per litre. It is a protection in the wort against the oxidation phenomenon. In the presence of oxygen it produces hydrogen peroxide; by this reaction it deprives
Chemistry of ascorbic acid titration with an oxidizing agent, and several procedures have been developed. The popular iodometry approach uses iodine in the presence of a starch indicator. Iodine is reduced by ascorbic acid, and, when all the ascorbic acid has reacted, the iodine is then in excess, forming a blue-black complex with the starch indicator. This indicates the end-point of the titration. As an alternative, ascorbic acid can be treated with iodine in excess, followed by back titration with sodium thiosulfate using starch as an indicator. This iodometric method has been revised to exploit reaction of ascorbic acid with iodate and iodide in