Grape quality and harvest time.
The control and assessment of the health of the vintage is a key point to guarantee the success of the production of a quality wine.
The elements that can alter the quality of the grape are:
• Favorable conditions for the development of berry rot fungi (Botrytis cinerea, among others) and the agents that cause acid rot, which greatly limit the quality of the grape; To control the health status of the grape, two parameters are mainly analyzed in the must: gluconic acid and volatile acidity.
• Presence of black fungi , which can cause OTA contamination.
• Hail or other accidents: if they occur 15 days before the harvest, it is recommended to anticipate it; If they occur 21 days before the foreseeable date of the grape harvest, healing and / or antibiotics treatments can be applied.
To decide the optimal date for the grape harvest, it is advisable to monitor the ripening of the grapes, analyzing the most important basic parameters that determine their quality:
• Weight of 100 berries
• Sugar content, measured by the Brix degree ( probable alcoholic strength)
• Acid content, measured by total acidity
• Gluconic acid to monitor health status
These parameters can be supplemented with sensory analysis of the berry and seeds , and others such as the content of polyphenols and anthocyanins , in the red grape.
The sampling of grape grains to carry out the analyzes should be done with a random collection in several areas of the vineyard and taking berries from different parts of the bunch, in order for the sample to be sufficiently representative.
Apart from the analytical parameters, several factors influence the decision to choose the precise moment to harvest the grapes:
• Climatic factors:
– Rains at harvest time: they can delay ripening or increase the weight of the berry by diluting its sugars; It is necessary to follow the weather forecasts when deciding the harvest date to avoid this phenomenon. If the rain has already caused this dilution, the harvest date must be delayed to recover the previous qualitative levels or improve them, provided that the presence of rot is very low.
– Water stress : if it is extreme, it can cause an incomplete ripening of the grape.
– Temperatures : if they are too high, they can cause dehydration, changes in the aromatic composition, increased sugar concentration due to dehydration, etc. If they are too low, they can cause a halt in ripening and / or a delay in the harvest.
• Health status of the grape , since the appearance of sources of rot without the possibility of paralyzing them with treatments may advise an early harvest (the safety periods of the products between treatment and harvest must be respected).