I notice some comments, observations and questions about pH adjustments in must from time to time. Last year I overshot additions of tartaric acid and wound up with a must of 2.68 and had to correct with bicarbonate to get it back up. What a mess. Wine turned out OK and even took a gold medal eventually at one of the amateur competitions. This year, my must pH just measured in at 3.99. I added 112 grams of tartaric acid (dry) to about 40 gallons of must (150 L), which was less than a third of what the usually recommended 1g/L called for to get the must down to 3.50 or so. After my addition, the pH levels just measured at 3.38, quite acceptable. S.G. initially was a whopping 1.128, and I added a L of distilled water and got it down to 1.120 and may dilute a bit further.
I know that there are a few variables in pH adjustments; buffering capacity of the grape must variety, S.G., temperature, etc. I just wish that there were some better estimations out there, which reflected more realistic "in the field" levels as it seems almost everyone overshoots the recommended dosages. Just some observations.
Ok dude, here is the answer to your issues, maybe. lol
Do not trust the 1g/L recommendation for changing pH or TA. In the past I would use that but add only 2/3 of that the calculation to the must and it still was overshooting the pH. I learned the best way to get the most accurate (although no perfect) correction is to do a bench trial s described below.
Strain 1 liter of must juice.
Add tartaric acid to this 1 L sample 0.5 g at a time and check pH each time. when it gets to the pH you desire, add that amount of tartaric acid to must.
Example of my Cab Franc this year:
My numbers were pH: 3.98 (Yikes) and TA: 6.2
For my practice, I like to end up with a pH of around 3.6 plus or minus 5. I expect fermentation and Malolactic fermentation to raise the pH possibly .15-.3 depending on the variability of the Must etc.
3.98 way too high for stability
I do bench trials always now to see how much tartaric acid to put in as estimating with equations does not give accurate results
I double or triple strain 1 liter of juice from the must and add 0.5 g tartacic acid at a time, mix and take pH every 0.5 g until I reach my target
pH bench trial results:
0.5 g: 3.87
1 g: 3.73
1.5 g: 3.61
2 g : 3.51 (TA: 8.4)
Choosing from these results is dealer's choice and gives options. For me I chose the 2 g/l option to get the pH in the 3.5 range as I know it “should” go up from fermentation, Malolactic fermentation, tartaric acid naturally falling out of solution and hopefully end up around 3.6-3.7. If it stays in the 3.5-3.6 range I am fine also as many great European wines are in that range as long as it is not too tart (I taste the juice). I have found with experience that adjustments of the must are well tolerated much better than later adjustments.
The way I calculate the must addition
pounds of grapes/ 15.5 = approximate amount of pressed juice/wine after fermentation.
So if you have 495 lbs grapes such I have for the cab franc, here is the calculation
495/15.5= 31.93 gallons juice.
31.93 gal x 3.785 L/Gal = 120.86 L of juice
120.86 L x 2 g/L = 241.72 g
so add 241.72 grams tartaric acid to the must then check pH later
Testing the Cab Franc Must a few days after adding the tartaric acid gives pH 3.50 to 3.58 depending on what part of the must tested (not perfectly homogenized) which is the range I like around starting fermentation. Luckily it does not taste tart either.
Now time will tell how much this will change and turn out but that is the fun of it as long as it is not overshot.
The Cab Franc today is almost done fermenting, Brix -0.3 one fermentation vessel an 0.3 other fermentation vessel. Wine not tasting tart despite the additions but very smooth. After I press tomorrow or the next day, I will recheck pH to see where it is at when the wine is more homogenized. but I expect everything to be on point.
Summary, do bench trial as discussed and you will get closer to real world result. Not perfect but much better than assuming the 1 g/l will reduce pH by 0.1 and increase the TA by 1 g/L as the books say.