To machine harvest, or not...

Lucinda Heyns - 21 Feb 2018

machine harvest 800p

Put a few winemakers in a room and ask their opinion about the quality of wine from machine harvested grapes…some will agree that machine harvesters are only suitable for lower tier wines and that premium wines require hand harvesting. Then there are others, who will happily harvest the grapes for their high end wines by machine. The reality is, there exists very little scientific evidence supporting either claims.

Machine harvesting is very common in New Zealand and in a 2011 publication NZ researchers reported that in general wine produced from machine harvested grapes contained higher thiol concentrations than hand harvested grapes. It was not the case for all wines analysed though. Here in South Africa where hand harvesting is still quite common the verdict is still out. Charles Hopkins from De Grendel winery, known for his boereproewe each year compared wines from the same S. blanc block made with machine versus hand harvested grapes. They were picked at exactly the same time (alternative rows) and treated exactly the same way in the cellar. Chemical analysis revealed no statistical differences between the two treatments but according to Charles he picked up a very definite sensory difference in the wines. The machine harvested wines displayed more tropical notes.

Researchers from UC Davis recently reviewed all published scientific articles which researched the impact of machine harvesting on wine quality. They also considered the latest investigations into new-generation harvesters and whether optical berry sorting could complement the use of machine harvesters.

Most studies indicate that the method of harvesting has an effect on the grape and wine composition. However, in the studies that evaluated the wines, the panel could barely distinguish the difference between wines made from machine harvested grapes versus wines from hand-picked grapes.

  • In one study, grapes and must from machine harvested grapes had a higher pH and 9% more phenolics compared to hand harvested grapes, probably because of increased skin maceration during mechanical harvesting. The resulting wines from machine harvested grapes however, contained less phenolics than the wine from hand harvested grapes. One explanation for this phenomenon could be oxidation, since machine harvested grapes are more exposed to oxygen during handling.
  • Another study compared harvest methods in both red and white varieties but the panel did not prefer one wine above the other.
  • A recent study by UC Davis used Pinot noir grapes and included a new generation mechanical harvester with optical sorting capabilities. Despite significant differences between phenolic and aroma compounds between the different harvest treatments, sensory analysis observed only small differences in the final wines. They analysed 18 attributes and only two, namely hue saturation and tropical fruit aroma, were significantly different.

Material other than grapes, berry damage, especially on more delicate varieties, and the resulting juice loss is still a major concern with machine harvesting. Machine harvester technology has however made progress in leaps and bounds over the years and many ‘delicate’ varieties are harvested successfully nowadays.

There are of course many factors that play a role in the quality of grapes delivered to a cellar, apart from the harvesting method. If temperature of the fruit is low and travel time to the cellar is minimised, coupled by the addition of sulphur, mechanically harvested grapes can reach the winery in good condition. More importantly, grapes should be processed soon after arrival to avoid unwanted extended skin contact.

One older study proved that optical berry sorting has the ability to segregate berries by ripeness levels which potentially impacts the final wine. This technology is however outdated by now and further research using new technology is required. Additional studies on the impact of machine harvesters using a wider array of cultivars could help to identify which varieties are most suited to machine harvesting.

Whether more research will finally put an end to the debate, only time will tell…

Link to Full article: http://www.asevcatalyst.org/content/catalyst/1/1/21.full.pdf

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