Electronic Sorting of Grapes

By Louis Nel

Sorting by hand

Sorting tables have been around for a while, but few people actually use them effectively as the volume of grapes and depth of the grape layer is often to great to insure proper sorting. The fact is also that if you want to sort your grapes effectively you need lots of people and slow, even feeding of grapes. Sorting should always be done in the vineyard first.

Tokara and Jan Boland Coetzee recently purchased rather unique sorting tables. The grapes are destalked and then put onto the sorting table that moves the berries by means of vibration. Sorting is then done removing leaves, stalks, snails and uncoloured berries that come through the destemmer. The grapes are then crushed and put into the fermenter. Using this technique 620kg of unwanted matter (excluding leaves and stalks from destalker) was removed from 20,06 tons of fruit in one block. This is a huge step forward towards better sorting.

In Spain, where this idea comes from, there are wineries that separate the top and bottom sections of grape bunches to make different wines from them.

Electronic sorting

Electronic sorting of fruit has been around for many years and is used very successfully in other industries although at huge initial cost.

An example of a system available in South Africa can be seen at SAD in Upington. Dried fruit is fed on a conveyer belt and then dropped onto another horizontal conveyer belt. Between these conveyer belts are censors and lasers that are connected to a computer. The computer has been programmed to distinguish between different coloured fruit by running fruit with desirable and undesirable qualities past it. If the computer recognises that fruit falling through the air does not meet the specifications it is shot out of the air by an air nozzle and then lands onto another conveyer belt (see Figure1).

SAD uses laser optics (SAD) and similar techniques are used to sort coffee beans (Realcoffee and Humboldfcoffee). Using RGB and infra-red cameras colours and shades can be distinguished. If this technology is taken further by using lasers, shapes can also be distinguished. Apples that have worms can be distinguished from healthy apples with laser technology (Photonics). Applications also include separating shrimp meat from peel, legs, eyes and heads (PthMagazine).

Using this technology you would be able to sort your individual berries looking for differences in size (eliminating small green berries or large berries), eliminate berries that are not properly coloured, eliminate stalks, leaves, pine needles, insects, botrytis berries, mealy bug berries, bird pecked berries etc. The list is endless. If the system is programmed correctly it would be able to tier your grapes into different classes.

The use of sensors to detect berry flavour is also being investigated in strawberries (see Italian site).

Bottom line

The possibilities that this technology has for wine quality is endless, but the implementation cost will be very high. A typical setup cost in the region of R2 000 000.