Problem with VA during MLF ?

[Falcon_wizard]

Good day everyone, I am reaching out to see if someone may be able to offer some useful guidance on a sauvignon blanc I am making from reconstituted juice I initially corrected the Ph/TA by adding 2mg/l of Tartaric Acid as the TA was quite low (4.5) and ph of 3.36. After primary fermentation however the ph was down at 2.9 and taste was very acidic. So I decided to undergo MLF to help tame acidity naturally before adding any potassium bicarbonate, although I was not initially planning to do MLF on it.

However two weeks into MLF at 68F/20C, I noticed a smell and taste that is similar to vinegar, however my carboy is topped up and also has a co2 blanket on that last two inches to protect it from oxidization. and I think my cleaning/desinfection regimen is quite solid.

Would you have suggestions on how to best proceed from here ? I could sulfite and stop MLF in case it was indeed acetobacter contamination even with a low oxigen/low ph, or rather let it carry through MLF and try to further tame down acidity with potassium adjustment if this is rather driven by the MLF itself ?

Thank you in advance for the feedback.

 

[Johnd]

I doubt seriously that MLF is proceeding in a wine with a pH of 2.9, and SB isn’t a wine that we typically want to undergo MLF.
So basically, you added too much acid to a wine with a good pH, and now have too much acid for your taste. MLF isn’t the solution that I’d employ. Add sulfite to protect the wine before anything else. I assume your wine is sufficiently aged to be free of all CO2 and to be evaluated. If not, allow it to age properly. Subsequently, perform bench trials with k-bicarbonate until you get the taste you want, then adjust your batch.

 

[Rice_Guy]

The pH drop you measured is normal for active yeast fermentation. When the CO2 dissipates it bounces back up.
? making wine ? the word of the day is patience

 

[JohnT]

SB is typically a high acid varietal, but it seems that yours tested low.

Questions:

can you tell us the total volume of wine and the total weight (or volume in teaspoons) of tartaric you added.
Also, how old was your ta test kit? if I look at you PH, you were just slightly low, if not even acceptable to some.

Fermentation IMHO should not lower the PH that much. most likely you added too much tartaric.

 

[Falcon_wizard]

Sure, its a 23L batch, and I’ve added 46g of tartaric acid (2g/L) I was trying to get TA to be within the 7-9 « texbook » range, but in hindsight looks like I would have been better to leave it alone or reduce the addition. The acid test kit was just purchased.

 

[Ajmassa]

a sauvignon blanc I am making from reconstituted juice

23L of reconstituted juice? This doesn’t happen to be a kit by any chance does it? If so that kinda changes things since acid levels on kits arent equivalent to levels typical of grape wines. So an ideal TA for this wine would seem skewed as different acids are used in different ratios to pre balance the juice. Which makes adjusting kit juice by testing levels almost a fools errand since we don’t know exactly where it ought to be once changed.
If this is the case I’d just let it age as others have said and then adjust up or down by taste using bench trials. And just forget about what the #s say

 

[stickman]

This is one of those unusual cases where the starting pH 3.36 was too low for the TA of 4.5, that is if the numbers are accurate. In general if the pH is below 3.6, the pH would be expected to drop to some extent during fermentation due to potassium bitartrate precipitation, and this pH drop will not come back up after CO2 is lost. As others have suggested, probably leaving it alone and adjusting to taste after fermentation would have been a reasonable approach.

I'll add the following information since we are already in the "black hole" of acid adjustment. TA is the tartness you taste, and textbooks might indicate this type of wine will finish in the 6 to 7 g/l TA, but that is your choice based on your taste. You also don't want an extremely low pH in the finished wine; you don't normally taste pH, but in the 2.9 range SO2 is volatile and will interfere with the aromatics.

So again, if the original numbers are correct, tartaric acid wouldn't be the best choice for a TA increase pre-fermentation. The reason is that usually tartaric acid is recommended because it delivers the greatest pH drop for the lowest TA addition, but the starting pH of 3.36 is already low enough, so this is the rare case where malic acid addition is the better choice for a TA increase. Malic acid buffers in the 3.5 pH range, so a TA adjustment with malic acid will have less effect on pH. Also note that because malic acid is lighter than tartaric, you adjust with less; the ratio of the molecular weights is 0.893, so you really add .893 gm/L malic acid to achieve a boost of 1 gm/L in the TA.

Post fermentation you can adjust with malic or tartaric, but you have to understand that cold stabilization will further lower the pH and also the TA, and to a greater extent if you use tartaric.

 

[Falcon_wizard]

It is indeed from a 23L juice pail, not a kit, however I have been told that those may in fact be reconstituted juice (although I cannot confirm 100%), hence why I mentioned it in case it would make a difference.

 

[Falcon_wizard]

This is extremely valuable insight... thank you. I did have malic acid on hand, but did not have the knowhow on when to use it... so based on the above, I’ll sulfite tonight to 0.8 molicular to stop MLF (if it did start), let things run their course for a bit and plan a bench trial in a few weeks to see if any further adjustments are needed. If there any value in racking now to try to get some of the volatile « vinegary » smell out at this time, or just simply wait ? I don’t mind waiting at all, but just trying to best course correct my previous mistake at the opportune time.