Grapevine & Wine 01/08/2011

Mechanized grape picking and post-harvesting treatments

It is important to set the mechanized harvester properly to improve the quality of the grapes and reduce the picking costs. It is also possible to intervene in the cellar

The mechanized harvesting allows a strong reduction of the costs but it is of capital importance to set the harvester properly, with a special attention to the number of beats per minute, in order to get the best quantitative and qualitative performances.

Bibliography reports that wines obtained by grapes gathered by mechanized harvesting are characterized by a reduced phenolic content in respect to handpicked grapes. This is normally due to oxidative phenomena. In the same way, the hand-harvested grapes show a smaller quantity of superior alcohols than the others. This difference can be explained by a smaller quantity of alcohols precursors and of oxygen in the must. These differences are obviously clear also at the sensorial level.

If setting the mechanized harvester properly can already lead to good results, it is clear that it is also necessary to pay attention to the post-harvesting treatments, in order to reduce the risk of pathologies, mainly the gray mould, and to preserve the polyphenolic and the anthocyanic content of the wine.

Moreover, given the attention of consumers for the content of sulfites, it is important to implement post-harvesting methods that reduce or eliminate sulfites. Nowadays technology can help a lot at this regard.

One possibility is ozone. A patent by PC Engineering shows the potentials of ozone to replace the standard methods employed to hygienize and stabilize the grapes after the harvesting during the whole wine-making process. Ozone can be used to disinfect the grapes after the harvesting and to clean all the tools used during the process and during the conversion of the must to wine. The advantages of the ozone are: i) reduction of the microbic population upon the grapes, ii) control of the microbic and oxidative condition of the must and wine without the use of chemicals and iii) stabilization of the final product without the use of metabiosulfites.

Another possibility is represented by the potassium sorbate together with ethanol. Bathing the grapes in a solution 10% ethanol and 10% potassium sorbate produces a reduction of pathogens to the same extent as sulfites, without contraindications.

It is also possible to employ chitosan together with UV-C rays, which has been proved as a very effective treatment especially for table grapes. The chitosan treatment can also be done on the field, two days before the harvesting, exposing the grapes after the harvesting to the UV-C rays, 5 minutes at 0.36 J/cm2.

Finally, interesting results can also be obtained by applying ethylene after the harvesting. Recent researches show that ethylene is able to increase the content of phenols, terpenoles, esters, alcohols and C6 compounds in the final product. Unfortunately this treatment can also increase the risk of gray mould development and reduces the global aromatic result.

di Ernesto Vania