Managing High Volatile Acidity in Red Grapes
Last updated: 10/2024
Applies to:Â Winemakers experiencing or anticipating issues with elevated volatile acidity (VA) in reds.
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 | WHY | RECOMMENDATION |
|---|---|---|
| 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 PRACTICE | WHY | RECOMMENDATION |
|---|---|---|
| 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:
If malic acid is < 0.1 g/L:
|
| 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 PRACTICE | WHY | RECOMMENDATION |
|---|---|---|
| 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:
| |
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™ or GO-FERM STEROL FLASH™ (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 PRACTICE | WHY | RECOMMENDATION |
|---|---|---|
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:
If malic acid >0.1 g/L, VA > 0.8 g/L, and fermentable sugar remains:
|
| 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 PRACTICE | WHY | RECOMMENDATION |
|---|---|---|
| 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. |
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