Selective Harvesting: Is It Right For Everyone?

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When it comes to selective harvesting methods in the vineyard, there is an assumption that these methods may not be economically feasible for large quantity-producing wineries, as selective harvesting almost always requires more time, effort, and man-hours in executing.  Past research has found that the yield and quality of grapes is highly variable in the vineyard, which gives opportunity for winegrowers to better manage their resources and harvest practices for the desired quality of wine produced.

What is “Selective Harvesting”?

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Selective harvesting is defined as the split picking of fruit according to their yield and quality, in order to monopolize on a specific quality level in the grapes, and ultimately, finished wine.  This is sometimes achieved by sorting the grapes in the field into different bins depending on quality criteria, or by harvesting different sections of the vineyard at different times, again depending on quality criteria.  Studies have shown that grapes harvested from different portions of a vineyard may have significant chemical or sensory characteristics, which are often due to variations in the land and soil underneath the vineyard.

Selective harvesting may be problematic at times, as sometimes a winery may only have access to a single crusher or a minimum tank size of 75 tons, which can make separating grapes into two bins at harvest an issue, as well as filling a single tank with enough juice from a smaller selective harvest.  One study demonstrated that a 3 hectare low-yielding vineyard could not produce enough grapes to fill a fermentation tank with juice, which may make selective harvesting of smaller areas difficult when only certain sized tanks are available for use.

Perceptions of Selective Harvesting in Australia

In general, Australian wineries have the view that selective harvesting is only appropriate for small boutique wineries, or very large wineries that have access to a wide variety of equipment.  Those wineries in Australia’s inland warm irrigated region, according to the authors of the study presented to you today, are under the assumption that selective harvesting is not within reach.  It is because of this assumption that Bramley et al, 2011 sought to examine this assumption more closely, and to either support or refute the idea using field experimentation and economic analysis.

How did they do it?

The vineyard for this study was a Cabernet Sauvignon vineyard, planted in 1994, and located at the Deakin Estate in the Murray Valley of northwest Victoria, Australia.  Plant vigor and grape yield was calculated using remotely sensed digital multispectral video imagery, as well by using mechanical harvesters with GPS and Farmscan equipment.  Zones within the vineyard were characterized by being either high-yielding or low-yielding based on information gathered by the aforementioned methods.  After determining the yield would be too low for the fermentation tanks at the low-yield site, another low-yield site (harboring grapes with very similar characteristics as the grapes from the original low-yield site) from a Cabernet Sauvignon vineyard at Deakin Estate was also included in order to obtain the minimum yield necessary to fill the fermentation tanks available.

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Grapes were monitored throughout the growing season, and were harvested at 24 ^oBrix.  12 random bunches were collected from each zone in order to measure bunch weight, mean berry weight, juice Brix, pH, titratable acidity, anthocyanins (color), and phenolics.  Wines were created from bow low-yield zones and the high-yield zones in small-lot winemaking methods and also at the commercial scale.  For small-lot winemaking, 200kg of grapes were harvested then subsampled into three 50kg batches, and malolactic fermentation was not allowed to occur.  Commerical wines were made in 75 ton fermentation tanks which were filled for high-yield zone wines and filled only to 51 tons for the low-yield zone wines.  Malolactic fermentation was allowed to proceed for the commercial wines.  Standard winemaking procedures were used for all wines.

Experimental wines underwent a sensory analysis by 25 untrained panelists and Compusense Five (a sensory software tool).  For each comparison, the first sample presented was the reference sample, which was followed by two other samples, one of which was the same as the reference sample.  Panelists were asked to smell and taste the samples and to identify which sample was the same as the reference sample and were asked to provide the reason for their choice.

What did they find?

• First and foremost, the authors noted a strong similarity between the remotely sensed data and the data collected from the GPS located on the harvesting machinery.  This provides evidence that the zones were actually separated properly into low-yield and high-yield zones. 

• Wines created from the low-yield zone and wines created from a mix of low-yield zones were not significantly different, indicating that it was appropriate to mix the two low-yield sites without lowering the overall quality of the wine.

• The wines from the high-yield zone tended to be more acidic and astringent than the wines from the low-yield zone.

• When wines were made commercially, there was a significant different between wines made from high-yield zone grapes and wines made from low-yield zone grapes.  The low-yield zone grapes tended to be fuller bodied and less astringent, and with a fruitier aroma than the high-yield zone grapes.

• Bunches from the high-yield zone were larger than those from the low-yield zone.  However, anthocyanin and phenolic concentrations were higher in wines made from low-yield zone grapes compared with high-yield zone grapes.  This result suggests greater wine quality in low-yield zone wines.

What do these results mean?

First, the results show that there are significant differences in yield and grape quality throughout different sections of a vineyard, which supports the need for purposeful zone delineation via posts, wires, or other means to separating sections of the vineyard.  Taking this one step further, another important result from the study is that if using remotely sensed data, it should be confirmed via ground-truthing (i.e. collecting information on the ground) to be certain the vineyard is being properly delineated.

The authors note that selective harvesting gives the winemaker greater control over the final blend of the wine, and ultimately the overall quality.  What many Australian winemakers are concerned about is the overall effect of cost when implementing such a strategy.  Even after taking in the harvest cost, the cost of small-lot winemaking, the harvest cost related to differing yield sizes, and total retail values (less expensive versus high-end prices), the researchers found that there was a total net benefit to a selective harvesting strategy.  See the table below (Table 2 from Bramley et al, 2011) for exact costs and benefits calculated.

Table 2 from Bramley et al, 2011

What about those vineyards that don’t make wine themselves?

There are many vineyards in Australia (and other places of the world, for that matter) that grow grapes to sell to other wineries, and not to make wine themselves.  Thereby, they do not have the added revenue of wine sold to add into the cost-benefit equation.  The authors were well aware of this fact, and performed a similar economic analysis to the one just mentioned, except leaving out the cost of winemaking and any potential wine revenue.  Even after taking these things into consideration, the researchers found that selective harvesting results in an increase in net financial benefit by more than 9% (in this particular example).  See the table below (Table 3 from Bramley et al, 2011) for exact costs and benefits calculated.

Table 3 from Bramley et al, 2011

Conclusions

The results of this study indicate that the notion that selective harvesting is only feasible for larger wineries with a variety of equipment sizes or small boutique wineries is incorrect, and that selecting harvesting may be financially feasible and beneficial for those wineries who undertake more large-scale production methods (at least in warm inland irrigated regions of Australia).  It is important to note that in order to maximize the benefit of selective harvesting, detailed analysis of the vineyard to delineate yield and quality zones must be confirmed using both remote sensing data and data collected directly from the ground.

Overall, I found this study interesting in that it showed that selective harvesting may be an option for all types of wineries, and is not limited to only those wineries with a greater variety of equipment or small boutique wineries.  One needs to remember, however, that this study occurred in a very specific wine region (warm inland irrigated region of Australia), the results of which may or may not be extrapolated to all wine regions around the world.  More research would need to be done to determine if this sort of harvest method is appropriate for wineries in any given wine region.

What do you all think of this topic?  If you’re curious to know more details about the methods or results of the study, please feel free to ask and I’ll see what I can find!

Please feel free to leave your comments below!

Reference:

Bramley, R.G.V., Ouzman, J., and Thornton, C. 2011. Selective harvesting is a feasible and profitable strategy even when grape and wine production is geared toward large fermentation volumes. Australian Journal of Grape and Wine Research 17: 298-305.

DOI: 10.1111/j.1755-0238.2011.00151.x

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