|In South Africa the price of grapes or wine was traditionally linked to the sugar content of the grapes or the subsequent alcohol content of the wine.
The higher the sugar content, the higher the price earned by the cellar or producer. This is obviously not quality based. Nowadays everyone is convinced that the quality of wine is determined mainly by the quality of the grapes and therefore it has become essential for the quality of the grapes to be properly managed by the cellars. Apart from the analytical grading, the most obvious grading method of grapes delivered to the cellar is visual judging. However, if visual judging takes place, but the grapes are not separated accordingly, it is of no value whatsoever. The use of sorting tables is a practice that enables the judging and separation of grapes that are delivered to the cellar.
In order to remain competitive internationally, cellars have to keep finding ways to ensure that their products comply with the required standards. The use of sorting tables for grapes is one way to ensure that this is the case. The removal of foreign or undesirable matter, for example leaves, insects, stones or equipment such as pruning shears or the removal of green grapes, damaged or rotten grapes, can therefore be ensured.
Sorting tables have undergone considerable development over the past few years and can be divided into two main groups. Firstly there are those that work with a conveyor or vibration where workers physically have to man the tables, and secondly there are those that use different automatisation techniques. This article addresses only the former, used for the sorting of grapes before destemming.
As mentioned above, sorting tables that use manual labour are divided into conveyor tables or vibration tables. In both instances that which has to be removed, must be done by hand. The speed control of such tables is critical to ensure that the correct balance between productivity and quality is maintained. Before purchasing or building such tables it is essential to talk to various fellow winemakers or suppliers to identify potential problem areas.
Because winemakers differ with regard to the processing of grapes, there is no single answer concerning the selection of the most suitable sorting table. Although the end result of a conveyor sorting table and one where the entire table vibrates is practically the same, there are important differences in sanitation. Vibration tables are easier to clean and although conveyor tables are usually cheaper, they do require more attention to cleaning, which is often not preferred by winemakers. In general vibration tables have two specific advantages, namely the natural distribution of the bunches on the table and the facility for smaller foreign objects to fall through. On the other hand vibration tables are noisy and in practice it is not so easy to be sorting from them.
Sorting tables are usually classified according to throughput in tons or kilograms of grapes per hour. It is therefore also important for sorting tables to be aligned, when purchased, with the crusher/destemmer that follows afterwards. The height of most sorting tables can also be adjusted to fit the sorters.
Eventually each cellar has to make its own decision about the kind of sorting table to be purchased and the financial investment has to be weighed up against the financial benefits. More information about various sorting tables can be obtained from the following websites:
Pregler, B. 2005. Wine Business Monthly 12 (12): 34 – 38.