Wine composition modifications

Finally, the adsorption of certain wine volatiles by the lees and the barrel itself (Chatonnet et al. 1992a Ramirez Ramirez et al. 2001 Jimdnez Moreno and Ancin Azpilicueta 2007), together with the possible changes that can occur during the additional bottle aging period (Pdrez-Prieto et al. 2003), will also cause modifications in the final aromatic composition of the wine. 

Due to their compositiou, musts and wines are acidobasic buffer solutious, i.e. a modification in their chemical composition produces ouly a limited variatiou iu pH. This explains the relatively small variations in the pH of must duriug alcoholic and malolactic fermentation. 

There is generally, however, a positive attitude toward physical treatments. They are theoretically more natural than chemical treatments and less likely to cause unacceptable modifications to a wine s chemical composition. It is, however, just as true that the effects of cold, and particularly heat, may cause appreciable changes, especially in colloidal structure. 

Strains of Lactobacillus fructivorans, L brevis and L hilgardii (heterofermentative bacilli) are frequently isolated from fortified wines with alcoholic strengths from 16 to 20% volume. They seem to be naturally adapted to ethanol but lose this adaptation after isolation. Strains of L fructivorans nevertheless remain very tolerant of ethanol, which has an activator role in their case (Kalmar, 1995). P. damnosus bacteria are not particularly resistant to alcohol, but the ropy strains multiply at the same rate and with the same yield in the presence or absence of 10-12% volume of alcohol. The adaptation phenomena are definitely dissimilar in nature. In most cases, they are the result of a structural (fatty acid, phospholipid and protein composition) and functional modification of the membrane. In the case of ropy P. damnosus... 

The spontaneous evolution of a mixture of species corresponds with the selection of those best adapted to wine—which is a hostile acidic and alcoholic environment. The composition of the plasmic membrane, and the various mechanisms, that permit it to react to the aggressiveness of the medium, seem to influence this adaptation. Certain species or strains may also differ in their ability to carry out these transformations. Strains of Lfructivorans adapt better to ethanol than L. plantarum and L. hilgardii, due to a more effective modification of their fatty acids (unsaturation and chain length) (Kalmar, 1995). Unsurprisingly, strains of this species are often identified in fortified wines tainted by lactic disease with an alcohol content between 15 and 20% volume. 

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