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Managing Underripeness Caused by Hot, Dry Growing Seasons

Last Updated: 6/2021

Applies to: grape growers and winemakers subject to post-veraison heat and drought in their growing regions. This article details how these conditions can cause underripe characters and offers vineyard and winemaking mitigation tactics.

Contains pdf download of an article written for VVQ - Vigne, Vini & Qualità magazine on how LALVIGNE products can reduce pyrazine levels.

How do heat and drought cause underripeness?

Heat waves and drought conditions cause uneven growth, sunburn and dehydration but, counterintuitively, they can also cause underripe characters. Hot and dry conditions can improve ripening and lower pyrazine levels; however, intense post-veraison heat and drought can have the opposite effect.

The hottest conditions can cause some of the slowest ripening and latest harvests. Grapevine stomata begin to close around 95°F, and higher temperatures can damage the photosynthetic apparatus and impair fruit ripening. After multiple days of high heat, vines may take several days to recover and some leaves may never recover due to irreversible damage (Keller, 2020). The vine essentially shuts down and ceases ripening during these conditions leading to slow flavor development and slow pyrazine degradation while dehydration increases sugar and acid concentrations.

Vineyard Mitigation

Bunch and canopy temperature are affected by three main factors: air temperature, absorbed radiation, and evaporative heat loss (transpiration) (Hayman et al., 2012). In hot, dry seasons or spells, vineyard tactics can be focused on the latter two to help minimize incoming radiation and maximize transpiration:

  • Minimize incoming radiation
    • Establish a good canopy in the early season when possible
    • Be strategic about leaf removal timing and intensity
    • Employ artificial shading (shadecloth and sunscreen) when suitable
    • Cover crops may help amount of reflected radiation from the vineyard floor
  • Maximize evapotranspiration rates (ETC)
    • Employ an irrigation strategy that makes sense for your vineyard and water availability to effectively utilize your canopy for cooling.

LALVIGNE foliar sprays are also a tactic for mitigating unbalanced ripening patterns. They are natural inactive yeast derivatives applied around veraison. They are compatible with regenerative agriculture and sustainable farming practices.

LALVIGNE works by activating the metabolic pathways that increase accumulation of phenolics and aromatic precursors. At the same time, they also activate the secondary metabolism of the vine that is correlated with increased pyrazine degradation (Suklje et al., 2016).

For an in-depth summary of the effects of LALVIGNE application on pyrazine levels, see this article by Lallemand R&D for VVQ - Vigne, Vini & Qualità:

Winemaking implications

Ultimately, heat and drought can result in long hang times, dehydration, and unbalanced grape composition (sugars, acid, phenolics, aroma compounds) - meaning lower yields and more difficult winemaking conditions.

Tips for dealing with underripe grapes:

  • Pre-fermentation:
    • Analysis is key! Berry sensory assessment and chemical analysis of must both be conducted to paint the full picture of the imbalance or underripeness you’re dealing with.
    • Eliminate MOG (material other than grapes) and stems as these can amplify herbaceous and green flavors
    • Treat the fruit gently throughout the process
    • Clarify pressed juice quickly and eliminate the press solids. Treat juice during settling to minimize and counterbalance vegetative flavors.
  • Fermentation:
    • Choose yeast and bacteria that optimize fruity flavors
    • Manage acid profile via both biological (malolactic fermentation) and chemical means
    • Ferment at a temperature that produces fruity secondary metabolites (esters)
    • Avoid using DAP as that will diminish the production of fruity flavors and promote the production of volatile sulfur compounds, which will heighten the green flavors
    • Mix the tank during the later stages of fermentation to keep the yeast in suspension and minimize yeast stress
    • Rack off fermentation solids as soon as possible


Learn More

For more information on making wine with underripe fruit including process and product recommendations, see our Best Practices Guides.

Interested in setting up a trial with LALVIGNE? Reach out and get in touch with our Vineyard Market Manager, Andy White, to learn more.

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Citations:

Battista, F. (2020). Pyrazines: the secret is to manage them in the vineyard. VVQ - Vigne, Vini & Qualità, 54–58.

Hayman, P., Longbottom, M., McCarthy, M., & Thomas, D. (2012, January). Managing vines during heatwaves. Wine Australia. https://www.wineaustralia.com/getmedia/90cf20af-1579-462d-b06e-35f343cbe129/201201_Managing-vines-during-heatwaves.pdf.

Keller, M. (2020). The Science of Grapevines: Anatomy and Physiology (3rd ed.). Academic Press/Elsevier.

Šuklje, K., Antalick, G., Buica, A., Coetzee, Z. A., Brand, J., Schmidtke, L. M., & Vivier, M. A. (2016). Inactive dry yeast application on grapes modify Sauvignon Blanc wine aroma. Food Chemistry, 197, 1073–1084. https://doi.org/10.1016/j.food...;