[Biodegradation of malic acid]
1993
Magyar, I.
High quality red wines don't contain malic acid because in a secondary fermentation biological degradation takes place. The process is also called malolactic fermentation and it is done by lactic acid bacteria that transform the malic acid into lactic acid and CO2. As a result of the process the wine becomes softer, more harmonic, and its pH rises. In case of white wines the process is not necessarily favourable because the lactic acid may deteriorate the wine's character especially that of softer varieties. Lactic acid bacteria can not reproduce themselves under 3.1 pH and when the free sulfurous acid content is above 10 mg/l. They are not able to synthesize a number of vitamins and amino acids; they get them from dead yeast cells. The optimal temperature of malolactic fermentation is 16-18 degrees C. So when the process is desirable sulphur should be avoided and pH may have to be raised above 3.2. Temperatures around 17 degrees C and keeping the new wine on feculence also speeds up the propagation of lactic acid bacteria. When someone wants to prevent malolactic fermentation, opposite measures must be taken
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