The serious dangers arising if premature arrest of alcoholic fermentation (stuck fermentation) occurs are well known. If sugar is present, bacteria development may increase volatile acidity.
There are several reasons explaining why such phenomena are more common today : 1) higher levels of alcohol ; 2) the more widespread use of closed vats for red wine where there is no contact with the air ; 3) intensive clarification of white musts ; 4) better management of problems related to difficult ends of fermentation.
Apart from insufficient yeasting and nutritional deficiencies (nitrogen), the causes of premature arrest are as follows. In red wines : 1) inadequate sulphiting of the harvest leading to early development of lactic bacteria ; 2) poorly controlled or excessive temperature, especially during yeast growth ; 3) insufficient aeration of yeasts during their growth. In white wines : 1) must extraction which is too rapid or excessive clarification ; 2) inadequate aeration ; 3) excessive temperature variations (thermal shocks).
If difficulties occur despite adequate precautions, the reasons for this may be found in the specific constitution of the must. However, a more likely cause may be human error.
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