What is Powdery Mildew?
A fungal disease that affects grapes and impacts not only grapevine health and yield but also significantly impacts grape/wine quality.
Why is it more prevalent this year?
Because of the growing season, which has been wetter than usual as well as warm – but not as excessively hot – as in previous vintages.
How does Powdery Mildew impact wine quality?
- It impacts flavour.
- It imparts a musty/mushroomy/mouldy aroma to the juice and wine.
- It can lead to high pH and higher potassium levels that impact the wine’s balance.
- It can lead to higher phenolic (bitterness, astringent) content but lower anthocyanins (colour).
- Increased risk of oxidation by laccase enzymes and elevated acetic acid largely due to secondary infections by other fungi (botrytis, sour rot).
- It impacts texture.
- It can impart an oiliness or yield a hollow wine if excessive fining performed.
- It impacts clarity, stability, and filterability.
- Powdery mildew increases the grapes own pathogenic (defense) response and drives grapes to produce higher protein content which additionally impacts colour stability, heat (protein) stability, and filterability.
- It impacts fermentation kinetics.
- Powdery depletes the nutrients and vitamins that yeasts need to thrive and ferment to completion.
- Powdery increases acetic acid (which can be inhibitory to yeast at a certain point).
- Powdery increases the likelihood of secondary infections by other fungi – this means there is more microbiological competition for the yeast to overcome and dominate the ferment.
What can we do in the winery to minimize the sensory impact of Powdery Mildew?
Whites & Roses
- Selectively hand harvest and/or sort.
- Process fruit immediately.
- Use whole bunch pressing and shorter press cycles where possible; use multiple press cuts to keep fractions separate by severity to dial in treatments and rates while minimizing over-fining. (*Often the first 150L/tonne are the most affected)
- Use a higher rate of SO2 depending on severity.
- If mouldy characters are observed, fine with bentonite (Bentogran, Microcol) at 200-300ppm, and/or casein (Casei Plus) at 50-300ppm, and/or Geosorb at 50-200ppm in the settling tank.
- Use a potent settling enzyme (Lafazym CL) to cold settle quickly, cleanly, and compact lees or use Vegeflot or Gelatine for settling using flotation.
- Keep juice lees separate; filter/process and do not reincorporate to free run.
- Check initial YAN levels and prepare to nutrify diligently.
- Forgo natural ferment and select a robust yeast that can ferment to completion with low nitrogen requirements (011 bio, Xorigin, RMS2), complement with a rehydration nutrient. (Superstart, Fermoplus Energy GLU)
- Nutrify diligently throughout ferment using a combination of organic and inorganic nitrogen. (Nutristart, Nutristart Organic, Enovit, Thiazote pH)
- Consider fermenting on low levels of oak alternatives to help build back mouthfeel volume – 1 stave/1000L or 0.1-0.2g/L of chips is often sufficient to support body without imparting overt oakiness. (Innerstave, Nobile)
- Assess once ferment is rolling and fine with an additional 100-300ppm Bentonite or Geosorb if required; supplement with yeast hulls next day to re-introduce turbidity and aid in keeping yeast suspended.
- Post ferment, rack off gross lees and SO2 immediately. (or vice versa as suits)
- Consider the addition of yeast-derived, mannoprotein-rich products (Oenolees, Batonnage Plus Elevage) for additional mouthfeel and complexity during aging.
- Conduct additional fining trials for heat stability and phenolics as needed.
- Use a glucanase (Extralyse) to aid in filterability 5-7 days before prefiltration.
- Selectively hand harvest and/or sort, use a higher rate of SO2 depending on severity.
- Process fruit immediately.
- Forgo coldsoak and consider a maceration enzyme (Lafase Fruit, Endozym Contact Pelliculaire) to improve rapid colour extraction.
- Forgo wild ferments, inoculate with a robust yeast and consider using a higher inoculation rate (300ppm); complement with a rehydration nutrient. (Superstart, Fermoplus Energy GLU)
- Incorporate sacrificial tannins (VR Supra, VR Color, Fermotan) and/or oak chips to help stabilize colour and bind up additional proteins while adding structure.
- Nutrify diligently throughout fermentation using a combination of organic and inorganic nitrogen. (Nutristart, Nutrstart Organic, Enovit, Thiazote pH)
- Forgo extended maceration and press wine tasting frequently and keep fractions separate as needed.
- Rack off gross lees as soon as possible, fine using Polymust Press, Gecoll Supra, Catalasi AF, or Gelsol to remove off flavours and improve mouthfeel.
- Trial aging and finishing tannins to improve the structure and mask off notes if needed.
These are guidelines only and are to be applied based on the extent of infection and condition of the fruit. All necessary viticultural prevention should be taken to prevent/minimize fungal infection.
Trials are always recommended when assessing dosage rates and product impacts on juice and wine.
Contact your local representative for product information and availability.
Inside Sales/ Winemaker
Wine, Cider & Spirits Product Sales Consultant