CHAPTER 2  

PRE-FERMENTATION STRATEGIES

Pre-fermentation operations performed between the grapes’ crushing and the start of fermentation have a widely underestimated impact on wine quality and its sensory stability during storage. A skin contact period of up to one day is frequently used to enhance aromatics by their extraction from the skins, provided that the grapes are perfectly ripe. More important than the technical modalities of pressing is the issue of the generally recommended addition of sulphur dioxide to must. The oxidation and browning of must resulting from omitting it is not related to the oxidation of wine, and even mitigates it by lowering detrimental phenols, thus improving the wine’s shelf life and reducing its astringency.Aroma losses frequently attributed to it only occur in a few specific grape varieties. Protein stabilisation by bentonite fining and any acidity corrections deemed necessary are already useful at this stage. Another important measure to achieve flawless wines with pristine aroma is juice clarification. Choice of clarification procedure is not decisive, but rather the level of clarification obtained, evaluated as residual turbidity. The use of pectolytic enzymes is strongly recommended for this purpose.

2.1 Must Acidification and the Issue of Safe pH

From a historical perspective, until the end of the twentieth century, must acidification had never played a major role in cool-climate growing areas. The acidity was usually high enough and often too high, so that deacidification was more important. High acidity was also accompanied by low pH, although this inverse correlation is weak. As is generally known in the wine industry, a low pH contributes to microbial safety. Hence, no thought had ever been given to microbial hazards caused by high pH levels. However, this situation has changed in the meantime, and the pH has become a hotly debated topic of conversation even in cool-climate areas. There are two reasons for that.

The first reason can be found in the development of the New World wine industry in the second half of the twentieth century. Most of their wine growing areas sprouted in hot regions that yielded low acidity and high pH figures. Therefore, acidification became a necessity to achieve a balanced taste and, at the same time, a decrease in pH to improve microbial safety. Since absolute safety was considered paramount, much importance was and still is attached to the lowering of pH to values considered safe through the addition of tartaric acid. As these countries quickly became opinion-leading in the global wine industry, the fear of supposedly too high pH levels spread to Old World wine-producing countries as well.

The second reason is global climate change. It has led to the fact that even in cool-climate growing areas, hot and dry vintages occur more often, providing musts with low acidity and actually high pH figures. That is why most of the countries concerned have now legalised must and wine acidification. This raises the question of how far the pH should be lowered and the acidity increased.

Interpreting pH Correctly

With a few exceptions, pH in musts ranges from 3.0 to 4.0. Some very conservative schools of thought continue advocating lowering pH to 3.5 for safety reasons and to add as much tartaric a