Veraison is here in many parts of GA – see the 10-day-old photo of a Merlot cluster (below) for proof.
Though I was not in Georgia for the previous veraison period, I know that veraison is a bit ahead of schedule this year. This is usually a welcomed occurrence as this could mean that harvest will follow suit. However, it is important to monitor maturity from here on out, as post-veraison weather patterns will greatly affect maturation rate. Use historical records as a guide, but don’t rely on them. I’ll leave it at that for now, as I will likely post something on monitoring maturity and deciding when to pick in early August.
What is veraison?
With this question, I’ll modify a reflection that I wrote up for the Cornell Lake Erie Research Program’s Crop Update late last August, when I was a Post-Doctoral Research Associate at the Cornell Lake Erie Research and Extension Laboratory (CLEREL).
In its most basic, simple, and popular terms, veraison marks color change in grapes. However, this is certainly not the only physiological change occurring in berries at this time… particularly in whites. If your Traminette grapes are turning red, they are not Traminette grapes. Veraison marks the stage that berries resume rapid growth (Fig. 1), primarily due to the influx of water and sugar. Note that sugar accumulation starts before anthocyanin (red/blue color pigments) accumulation at the onset of veraison (Fig. 1) and, therefore, there is measurable sugar in green grapes as veraison begins. Veraison is a transitional period during berry development that delineates the berry formation and development stage (before lag phase, Fig. 1) from the berry ripening stage (after lag phase, Fig. 1). Changes manifested in berries throughout veraison, that continue to lesser or greater extents through harvest, include berry softening, sugar accumulation, acid degradation and/or dilution, and accumulation/degradation of sensory impact compounds (often variety-specific, but things like anthocyanins, methoxypyrazines, trans-2-hexanal, norisoprenoids, etc). These physiological processes make the grape (now containing seeds viable to germinate), more palatable, an evolutionary tactic to attract seed dispersers. However, these same processes make the grape (and its many value added products) attractive to humans, which is why we cultivate grapes.
When are you officially at veraison?
As mentioned above, veraison is a transitional period. It starts with berry softening and sugar accumulation and ends… well, I am honestly not sure if I know when veraison officially ends… do you? In fact, when veraison begins is almost as elusive as when it ends. The timing of veraison is affected by variety (i.e. veraison typically starts __ days after bloom in __ variety), but also meso-climate within a given region. For example, to my knowledge, color change has not started in vinifera reds in Tiger, GA, but is well on its way in Cleveland and Dahlonega, GA. What marks official veraison? When I was at the CLEREL in NY, we called official veraison at what I could tell to be about 35-50% of Concord clusters containing some (a very subjective term) color. I once saw a poster that marked veraison at 5% color. I have also heard veraison is “50% of color in 50% of the clusters” – I guess this means when 25% of the total berries in the vineyard are colored. In Virginia, our research team called veraison to be when 50% of all berries were colored – but we never officially quantified this. My personal favorite, and likely the most practical, was when a grower said “I know its veraison when I look into my canopy and see some color.” I am not sure any of these “veraisons” are right or wrong. I guess it really does not much matter when veraison begins and/or ends. As long as it happens, it will mean that we are into the ripening period – an exciting place to be! I would advise all to use their historical official indicator” of veraison, and stick with it for annual consistency.
Veraison-time reminder: At this time, I would encourage those that have had historical bird and/or vertebrate pest pressures in their vineyard to deploy their preferred deterrence and prevention measures. Those who have experienced such pressures know to not underestimate the amount of crop that can be lost to these pests.
Further reading / literature cited:
Coombe, B.C. 2001. Ripening berries – a critical issue. Australian Viticulture 5: 28-34.
Keller, M. 2010. The Science of Grapevines: Anatomy and Physiology, 1st Ed. Academic Press.