Cluster Thinning Reduces the Economic Sustainability of Riesling Production

RESEARCH IN PLAIN ENGLISH

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(2013) American Journal of Enology and Viticulture 64:333-341

Trent Preszler, Todd M. Schmit and Justine E. Vanden Heuvel
​Summary by Amanda Garris

Why?

Do lower yielding vines result in higher quality wine? Wine critics think so, but many growers have to consider the economic sustainability of yield-reduction practices. There are few tools to help wine producers calculate the actual costs and benefits of yield-reducing treatments such as cluster thinning. Our goal was to evaluate the effect of cluster thinning on yield, fruit composition, wine aroma and financial net returns to help wine producers make decisions about cluster thinning.

How?

This field experiment was conducted from 2008 to 2010 at a commercial Riesling vineyard on the east side of Cayuga Lake in King Ferry, New York, in the Finger Lakes. 16 plots of 7 vines each were randomly assigned to one of four levels of cluster thinning:  no thinning, 1.0 clusters per shoot (low crop), 1.5 clusters per shoot (medium crop), and 2.0 clusters per shoot (high crop). Cluster thinning took place when at least two-thirds of the vines had pea-sized berries. Clusters located close to the growing shoot tip were removed first, and the basal clusters were left intact. We collected data on berry weight, yield per vine, average cluster weight, canopy light environment, and (during winter) bud cold hardiness. Juice was analyzed for soluble solids, pH and titratable acidity, and wine was made using standard procedures. The aromas of the wines were analyzed by a sensory panel which grouped the wines by similarity. The economic analysis incorporated yield, market price and production costs.

What we learned

  • Cluster thinning had little or no effect on berry size, pH, titratable acidity, pruning weight, cluster light exposure, or bud cold hardiness.
  • Cluster thinning enhanced fruit ripening, and Brix was consistently higher in grapes from the low cropped compared to the non-cluster thinned vines, but the degree of difference varied by year.
  • Panelists were able to discern differences among wines made from vines with different levels of cluster thinning. In 2009, with the low crop was grouped by the panelists as distinct from the others, and in 2009 and the low and medium crop were grouped separately from the high and non-thinned crops. In 2010, all four levels of cropping could be distinguished by panelists.
  • The price premium required to offset the loss in income from cluster thinning varied by year, but for the lowest crop level, recouping lost net returns would have required grape price increases of 143%, 139% and28% in 2008, 2009 and 2010, respectively.
  • Net economic returns on a per acre basis were significantly reduced by cluster thinning, but in several instances the wines from those treatments could not be differentiated by the sensory panel.

The bottom line

The financial losses due to cluster thinning can be recouped a significant increase in market price, up to 143% over the base market price, but the resulting wines are not always perceived as different by a consumer panel.

Amanda Garris is a freelance writer based in Geneva, NY.