The basis for the decline in fermentation rate is not fully understood.
The increase in alcoholic fermentation rate by the addition of selected
yeasts strains to the must could result ineffective so the residual sugars
were also utilized by contaminating microorganisms able to carry out
unwished metabolic pathways. Such an example, in these conditions,
some heterofermentative lactic acid bacteria strains could significantly
increase volatile acidity inducing a remarkable loss of quality of the
alcoholic beverage. Moreover, yeasts lysis, occurring at the end of
alcoholic fermentation, determines the solubilisation of cellular
contents which can greatly stimulate Brettanomyces spp. growth