Grapevine & Wine 06/05/2013

To preserve quality of grapes harvested by machines

Many negative effects of mechanical harvesting of grapes are attributed to damage and subsequent leakage of juice, often accentuated by high time between harvest and processing as well as high temperature

The presence of must in the product harvested by machine, which can reach very high levels (25-30% of the total mass), can cause several negative effects such as oxidation of phenolics, abnormal fermentation, skins maceration, etc. For that reason, an innovative system of handling and grapes transporting was developed in order to separate, once harvested, the liquid part (must) from the solid one (bunch of grapes and single grape), and then to apply different working processes to each of them. Thanks to this system, it was possible to isolate the must in a closed tank and thus, immediately, preserve it by dry ice or liquid carbon dioxide, with the addition of enological chemicals (sulphur dioxide, ascorbic acid and tannin) to avoid chemical and microbiological modifications. The evaluation of wines throughout tests and sensorial analysis highlighted the better quality of the wines obtained by the proposed technique compared with the traditional one. This was related to the greater presence of primary fragrances, better color, and a better balanced structure of the wine preserved against oxidation action.

The concentration of protein and phenolic compounds in juice and wine from hand harvested and mechanically harvested ‘Sauvignon blanc’ grapes was determined under different juice processing conditions. Destemming and crushing resulted in higher concentrations of protein and phenolics in the resultant juice. Most of the proteins and phenolics were extracted in the 0-0.4 MPa pressing. Juice and wine from mechanically harvested grapes consistently showed lower protein level than that from hand harvested grapes under the same juice processing conditions, but no significant difference was detected in phenolic content. The results suggest wines from mechanically harvested grapes with lower protein content might require less bentonite for protein stabilization.

The objective of the some Italian experimental works were to compare two types of grape harvesting machines, one using horizontal shaking (SO) and another using vertical shaking (SV). The trials were carried out on Trebbiano Romagnolo cultivar trained by Casarsa and GDC system. During the trials the extent of the vibrations transferred from the shaker on the effects on the products, on the plants and the final features of the wine were evaluated. The results have shown differences between the two grape harvesting machines and to a lesser extent between the adjustments used with each machine. The extent and the duration of the vibrations transmitted have affected the mistreatment of the vines, the harvest characteristics and the results of the enological transformation. The vertical shaking system has allowed a better overall performance due to a closer interaction between the plant and the machine.

di R. T.