1 INTRODUCTION
Current trends are moving increasingly towards the mechanisation of the harvesting process. For a cellar to receive mechanically harvested grapes, it is necessary to make a few adjustments with regard to the offloading system, grape crusher and preparation of grapes so that the operations may proceed optimally.
2 OFFLOADING SYSTEM
The ramp towards the offloading system must not be too steep, in order to prevent loss of juice as a result of overflowing pressing bins. It is therefore important that the pressing bins which transport the mechanically harvested grapes should not be too full. A drainage system is recommended for the receiving bin. The system comprises a series of sieves in the receiving bin for the juice to drain into the outlet pipe. It is necessary for the outlet pipe to have a valve for controlling the juice flow.
To prevent the mechanically harvested grapes from flowing uncontrollably through the outlet opening into the grape crusher, it is advisable to make use of a hydraulic door to shut off the outlet opening. This not only prevents the uncontrolled flow of juice and skins to the grape crusher, but also allows for sufficient time to drain the excess juice from the receiving bin. The design of the receiving bin should limit microbiological contamination.
3 GRAPE CRUSHER
The grape crusher must have splashboards to prevent loss of juice. The use of a magnet at the grape crusher is strongly advised to ensure that all iron objects which could possibly damage the pneumatic bladder are removed from the juice and skins. The design of the grape crusher must allow for various options, for example destemming or not. This will be very convenient when there is a combination of mechanically and manually harvested grapes.
4 PREPARATION OF GRAPES
4.1 Quality of block
Thorough inspection of the block must be done beforehand to identify and remove any infected grapes or other conditions which may have a negative quality influence on the block.
4.2 Cultivar
Temperature sensitivity and vinification style must be taken into account so that the necessary adjustments may be made, should there be a need for oxidative or reductive processes. Red cultivars may be pressed later in the day, for example.
4.3 Time between harvest and crushing
This period of time is critical for mechanically harvested grapes and simulates direct skin contact as it occurs in the cellar. The longer this period and the higher the temperature, the higher the extraction of phenols, heat labile proteins and potash. If the temperature in the vineyard becomes too high, loads should be kept smaller and delivered more often to the cellar.
Should there be any further enquiries, contact Eugene van Zyl at 082 577 2758.
Wynboer is incorporated in WineLand, magazine of the SA wine producers.
