3.2.1.c Sorting in the winery

Sorting in the winery is made possible by various equipment that makes up the sorting lines. Sorting can be manual with the help of vibrating or non-vibrating manual sorting tables or automatic using the principle of optical sorting or a densimetric bath.

The berries, even if healthy, are not always of good quality, such as the pink berries sometimes found in the harvest. This can be due to a high yield, flowering that was disrupted by the weather or severe water stress.

The damaged berries can be of several sorts, they can be damaged by agricultural machinery or by fungal diseases (powdery or downy mildew, or Botrytis). When the berries are affected by one of these diseases, it is possible to have not only quantitative losses, but also qualitative losses which impact the must and later the wine. The risk and nature of organoleptic impacts depend on the type of disease.

When the vineyard is affected by powdery mildew (Uncinula necator), the berries may show several symptoms (Fungal disease management), in each case causing a quantitative loss of the harvest. Unfortunately, powdery mildew can also affect the quality of a red wine by changing the grapes' composition. Powdery mildew contamination causes an increase in herbaceous aromas, proportional to the percentage of powdery mildew and a mushroom-like odour. The aromatic modification is significant from 9 to 13% of powdery mildew and deeply modifies the olfactory profile of the wines. It also results in a decrease in tartaric acid and an increase in pH.

Contamination by downy mildew (Plasmopara viticola) also results in partial to total loss of harvest quantity (Fungal disease management). Contamination affects the developing organs and goes through several stages. Attacks at flowering and fruit set are classified as grey rot, while later symptoms, appearing on bunches, produce brown rot. A study has shown the detrimental qualitative impact of downy mildew. Late attacks of mildew resulting in brown rot appearance modify both the aromas and flavours of the wine.

The wines have more vegetal notes, due to a high methyl salicylate content and less fruit, total acidity increases and pH decreases. With a 5% attack rate, the quality of the wine appears to deteriorate significantly. It is therefore advisable to avoid exceeding this threshold.

Finally, Botrytis cinerea can cause rot phenomena (Fungal disease management)), that are favourable to the production of sweet wines when it is noble rot, and unfavourable to the production of dry white wines and red wines when it is grey rot. This fungus produces an oxidase enzyme, laccase, which is responsible for the oxidation of polyphenols in wines. Grey rot also causes aromatic deviations with the development of characteristic "musty" or "undergrowth" odours as well as colour deterioration. It is imperative to remove all the botrytized berries and, when necessary, to add sulphur to the harvest.