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Managing High Volatile Acidity in Red Grapes

Last updated: 9/2022

Applies to: Winemakers experiencing or anticipating issues with elevated volatile acidity (VA) in reds.

*Note for harvest 2022: we've received a lot of calls about abnormally high VA in red grapes, especially in Northern California. This VA is occurring with and without visible signs of rot and with and without the presence of spoilage yeast and bacteria. We don't have a full understanding of why this is happening, but we do understand how to mitigate the effects.

Problems with high volatile acidity (VA):

  • Acetic acid, a major contributor to volatile acidity, is inhibitory to yeast. It can cause problems at concentrations > 0.6 g/L and cause stuck fermentations at concentrations > 0.8 g/L.
  • Sensory impacts
  • Legal limitation in wine of 1.2 g/L whites, 1.4 g/L reds

Managing High VA

See the guide below, organized by winemaking stage, for our best recommendations on managing this issue.

Vineyard/Transportation

BEST PRACTICE

WHYRECOMMENDATION
Minimize time between picking and processing as much as possible.Minimize time fruit is left unprotected from microbial spoilage.
Add an antimicrobial product to the picking bins (SO2 and/or a non-Saccharomyces yeast).Limit the activity of VA-producing native microflora by inhibiting them (SO2) or by outcompeting them (non-Saccharomyces yeast).

Receival/Processing

BEST PRACTICEWHYRECOMMENDATION
Sanitize your fruit processing equipment between lots.

Avoid cross-contamination between lots of fruit.

Consider adding a non-Saccharomyces yeast to the tank if you did not add one to the picking bins.Non-Saccharomyces yeast can outcompete VA-producing native microflora prior to initiating alcoholic fermentation.Use GAIA or LEVEL2 INITIA.
Run juice analysis ASAP, including VA (acetic acid) and malic acid.

Getting a baseline for chemical parameters allows you to track trends and make data-based decisions.

Send out for an ETS Laboratories Juice Panel if you do not have in-house analysis abilities.

Be as aggressive as possible with antimicrobials, considering the amount of remaining malic acid (progress of malolactic fermentation).

Control VA-producing spoilage microorganisms without inhibiting malolactic fermentation.

The amount of remaining malic acid will determine how aggressive you can be with antimicrobial action.

If malic acid is > 0.1 g/L:

  • Add up to 50 ppm SO2 (amend this rate if you added SO2 to picking bins)
  • Add 20 g/hL BACTILESS™ which inhibits VA-causing acetic and lactic acid bacteria. Add BACTILESS directly to the liquid, not the skins.

If malic acid is < 0.1 g/L:

  • Add up to 75 ppm SO2 (amend this rate if you added SO2 to picking bins)
  • Run microbial analysis (ETS Laboratories Scorpion Analysis). Note: this must be done PRIOR to adding BACTILESS™.
  • Add 20 g/hL BACTILESS which inhibits VA-causing acetic and lactic acid bacteria. Add BACTILESS directly to the liquid, not the skins.
Do not conduct a cold soak.

Saccharomyces can outcompete VA-producing spoilage organisms and cold soaks increase the amount of time before Saccharomyces is active.

Initiate alcoholic fermentation as soon as possible.

Alcoholic Fermentation

Our recommendations for alcoholic fermentation with high VA are based on limiting as many antagonistic fermentation conditions as possible:

BEST PRACTICEWHYRECOMMENDATION
Use a yeast strain that is a strong fermenter that can stand up to VA and has a short lag phase.The faster Saccharomyces starts fermenting (short lag phase), the faster it can outcompete potential spoilage organisms.Use ALCHEMY IV, ENOFERM CSM™, LALVIN DV10™,LALVIN EC1118™,LALVIN ICV D21™, LALVIN ICV GRE™ or LALVIN T73™
Do not co-inoculate with malolactic bacteria.

These fermentations are not candidates for co-inoculation because:

  • Residual antimicrobial agents may remain at the beginning of alcoholic fermentation
  • There is potential for VA production from malolactic bacteria during these higher risk fermentations

Use a rehydration protector (nutrient).

Nutrients necessary for alcoholic fermentation may be depleted due to the activity of VA-producing spoilage organisms.

Use GO-FERM PROTECT EVOLUTION™ (must be kept in the correct 1.25 : 1 ratio with yeast).
Use a higher dose rate for yeast.

Adding more yeast at inoculation will allow active fermentation to begin more quickly and decreases the amount of time it takes the yeast to reach maximum cell density.

Inoculate with 30-40 g/hL yeast.

Use fermentation nutrients.Nutrients necessary for alcoholic fermentation may be depleted due to the activity of VA-producing spoilage organisms.Use our Fermentation Nutrition Planner to develop a yeast nutrition plan.
Ferment at a cooler temperature.Limit antagonistic effect of heat and acetic acid especially as alcohol increases.

Maximum temperature recommended is 28°C/82°F.

Avoid extended maceration.When alcoholic fermentation is complete, Saccharomyces is not outcompeting spoilage organisms and wine conditions are optimal for the growth of spoilage organisms.

Sluggish/Stuck Fermentation

Unfortunately, even with these best practices to prevent a stuck fermentation, it may be that fermentation will stop. Consider restarting your fermentation if the fermentation slows and the rate of sugar depletion is <0.25 °Brix per day. If you find yourself in this situation:

BEST PRACTICEWHYRECOMMENDATION

Detoxify the fermentation.

During a stuck fermentation, yeast become stressed and can produce certain short-and medium-chain fatty acids. These fatty acids can inhibit the yeast used for the restart.Add 40 g/hL RESKUE™ to remove short- and medium-chain fatty acids.

Run a chemical panel including malic acid, VA (acetic acid), glucose/fructose, and alcohol.

Check the status of alcoholic fermentation (how difficult will a restart be?), the status of malolactic fermentation (does MLF need to be completed?), and the current level of VA (how difficult will MLF be?).

Use ETS Laboratories if you do not have in-house analysis abilities.

If VA is very high, VA removal may be necessary. Call us for more information.

Develop a restart plan based on the progression of alcoholic fermentation and the level of remaining malic acid.

The amount of remaining malic acid will determine the appropriate antimicrobial agent to use (does the wine still need to undergo malolactic fermentation?).

If malic acid <0.1 g/L:

  • Press
  • Add another 20 g/hL BACTILESS
  • Initiate a restart

If malic acid >0.1 g/L, VA > 0.8 g/L, and fermentable sugar remains:

  • Press
  • Add 25 g/hL lysozyme
  • Initiate a restart
Restart the fermentation with this protocol using UVAFERM 43 RESTART™.We have found this protocol to be the most effective way to restart difficult stuck fermentations. UVAFERM 43 RESTART is pre-acclimated to difficult fermentation conditions.Start at step 4 if you have already added RESKUE.

MALOLACTIC FERMENTATION (MLF)

BEST PRACTICEWHYRECOMMENDATION
After alcoholic fermentation, run a full chemical panel including malic acid.Determine if MLF still needs to be conducted and determine if other wine conditions will be antagonistic to malolactic bacteria.Use ETS Laboratories if you do not have in-house abilities.

Initiate MLF as soon as possible if malic acid remains.

The sooner MLF is complete, the sooner the wine can be stabilized.

If BACTILESS has been added: rack off primary lees, and rack again 24 hours later. Then, initiate MLF with a double dose of LALVIN VP41™ (strain most compatible with BACTILESS)

If lysozyme was added: MLF can be initiated 4 days post-addition in full-bodied reds. In light-bodied reds, inactivate lysozyme with 5 g/hL bentonite (GRANUBENT PORE-TEC) prior to initiating MLF using your preferred malolactic bacteria

When MLF is complete, stabilize the wine as soon as possible with method of choice (SO2, filtration, etc).Confirm microbial status of wine with microbial analysis (ETS Laboratories Scorpion Analysis). If you have added BACTILESS, Scorpion analysis must be conducted 30 days after the last BACTILESS addition.

Contact Us

Still having issues or questions about this subject? Contact us to speak with a member of our technical team.

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