Ask the Winemakers: Fermentation pH, Acid, SO2

Question from a reader who left a message on SHW’s website page,  Ask the Winemakers

“what should I do……… pH 4.08 TA 5.4 VA 0.34 Malic Acid 1.7 Total SO2 20 Free SO2 2 I want to add Tartaric acid, I just don’t know how much so I can decrease my pH. However I also don’t want my TA to rise much more, around 6.0-7.0. Please help!!!!”

“Ooops…. forgot to give more info. I have a small batch of Zin from my backyard, 4.5 gallons.”

SHW mentor Don Koehler responds:

First of all, don’t panic. You are doing ok, with a couple of adjustments.

Targets for red wines: pH in the 3.6 – 3.7 range. TA can go up to 7.0 or 7.5. (e.g. see the Beverage People catalog and manual from Santa Rosa as an example)

1. Your pH does need to come down. My experience is that 1 gram/liter tartaric acid usually lowers pH about 0.15 units. So if you add 2 grams/liter tartaric acid, you should approach 3.7. Most directions say do not add more than 2 g/L at one time. You can do another adjustment later, if needed. (note: this is grams per liter, not grams per gallon)

2. So you have about 17 liters. of wine. Add 34 grams tartaric which should lower your pH towards 3.7, and raise your TA towards 7.5, but that is ok. You will see a definite improvement in fruit and flavor as the pH goes down. If it seems sharp at first, don’t worry, revisit it in a few weeks and taste it again.

3. If you are not doing malo lactic fermentation, which you do not need to do, you can add SO2 at 50 ppm, to protect your wine now, after fermentation. (If you were planning on doing ML, lower the pH with acid, but do not add the SO2 until the ML is done – a few weeks or a month from now.)

4. You have 4.5 gallons of wine, – in what? If you have 4.5 gallons in a 5 gallon carboy, you need to top that baby up to the top, period. Buy a few bottles of some decent, not expensive, but not sweet zin and add it to yours to get the carboy full. Nothing else works. Or find someone that is making some petite sirah, which is a good blender with zin, and top it up with that. Or find someone with a little extra zin and use that. The carboy has to be full to protect the wine. CO2 or argon do not adequately protect a not-full carboy. You have to get the air (read oxygen) out.

5. On SO2 management: a chart which shows how to make up a 10% solution of SO2 and how many milliliters of it to add to get a given ppm of SO2 in your wine. The second chart shows how many ppm of SO2 you need in your wine to get to 0.5 molecular SO2. Molecular is the active species of the chemical, and varies with pH. So assuming you get close to 3.7, you want to have 40 ppm free SO2 for the 0.5 molecular level. So that is why I suggested above to add 50 ppm SO2, since some will get bound up and you might not get down to pH 3.7 with the acid addition.

6. At this point, bound SO2 is fairly irrelevant, and so is TA, for that matter. Follow pH from here on out and get your wine into the 3.6 – 3.7 range by Thanksgiving or Christmas. You will see some acid settle out and form a red crust at the bottom of the carboy when you rack, but that is ok. Just follow the pH, and add a little more acid, especially if the pH gets over 3.75.

I hope this helps. I have been making wine a long time, and these procedures have worked well for me. I grow grapes here in Loomis, and make wine from them. It is not unusual for the pH to jump with these valley grapes after fermentation is done, so that is likely how yours got to 4.0 or more. But it is correctable, and everything should work out.

“…I have looked at so many websites I have become partially confused about the addition of acid. Again thank you.

So currently I have my wine must in a 7.5 gallon food grade white bucket. It has already fermented dry and I did add ML. Questions: Do I add the tartaric acid then press? Do I add and then wait 2-3 days then press? Do I press then add the tartaric acid? I have 1g, 3g and 5g glass carboys.

After getting my results from Lodi Wine Lab I was concerned not having enough free SO2 for ML to complete. Adding the tartaric acid and lowering the ph……will that help the wine from getting unwanted bacteria and off smells? Or should I add a touch of SO2? I know that I need to keep my SO2 level below 15ppm for ML to complete.”

Thanks for the additional info. I did not realize you still were working with your must, so that affects some of the calculations.

1. As long as your must has a cap on it, it is protecting itself by generating the CO2, which tends to form a blanket on top of the cap. Your hydrometer readings can actually go down to – 2.5 brix before fermentation is totally done. (the alcohol lowers the specific gravity of the wine, so you can get minus readings – with pure water being 0.0) So keep your vessel covered with the lid, or a plastic garbage bag or something impermeable to air, to try and keep CO2 in and air out.

As long as you have a cap, you can extend your fermentation for a while. If/when the cap totally sinks into the wine, you have to press immediately. That day, that hour! Because there is no more CO2 coming off to protect the wine. When you get towards the end like this, you can also punch down once a day instead of twice or more, to allow the cap to reform and help protect the wine.

2. Add your tartaric acid now, dissolve it in some of the wine, mix well, and maybe wait a day or three before pressing, as long as you have a cap. Your acid addition should be based on gallons of wine, not must. So your 4.5 gallons of must probably contains 3 gallons of wine. 2/3 or 70% is a usual fraction of wine in must. So make your acid addition based on wine gallons – 3 gallons or whatever you estimate you have.

3. Do not add any more SO2 now. Let the malo work. After pressing, top up the containers, and the wine will be protected adequately for some weeks , if needed. Young wines have some inherent protection in them. Just keep them away from air. Let malo finish before adding more SO2.

4. Again, make any future SO2 additions based on gallons of wine.