For this example, let's put everything together by taking a look at how we might deal with 25 gallons of Syrah must that is at 27.5º Brix, with a pH of 3.95 and 5g/L TA. Fruit with these starting numbers will definitely need some work before yeast can or should be added. The first step is to dilute the sugars, and then tackle adjusting the pH and TA. Adjusting the sugars first is advisable because the amount of water needed to make the dilution is usually much greater than the amount needed to make a pH and TA adjustment. Once the sugars are within the desired range, we can then go ahead and address the pH and TA without notably impacting the ºBrix at that point.
Let's discuss the method we'll use to lower pH. Our goal is a wine that finishes around 3.6 pH. Since we will also be doing an MLF (raises pH), we could add enough acid to to bring the pH to 3.5. Once MLF brought it back up to 3.6ish, we'd be in great shape.... on paper. However, in reality, adding enough acid to create a .45 pH drop is quite intense and we may find ourselves shooting even lower than our targeted range of 3.5 by accident. In addition, the taste will be very sharp. This much artificially introduced acid will have a hard time integrating harmoniously into the wine. As stated before, if you need to make a large adjustment, it's best to do most of it in the must, but there are limits.
With that in mind, it is probably best to compromise and target closer to around the 3.7 pH range. Calculate the amount of tartaric acid needed to raise the TA of the must by 2.5 g/L (or 0.25%). Given our original figure of 5g/L, our TA will be 7.5 g/L along with a drop in the pH to around 3.7. The numbers won't line up perfectly like this once the addition is made, but it will put you into a generally acceptable pH and TA range. When tasting after the addition, it's possible that it will be in balance already. Your original "too small" addition may be all that is needed. As with any addition, even smaller ones, we should still effect it in a conservative manner. Add a portion of the addition, mix, test, and taste. Decide if the rest is needed. Besides being safe, this incremental acidulation while tasting will teach you how the balance of the must changes as the pH and TA come into the correct range. This will help you to develop your palette for the future- not only for must adjustment, but for the finished wine as well.
Adjust the pH / TA: When acidulating the must, only 60-70% of the must volume is juice. For TA and pH adjustments, we should only be using the amount of juice in the must, rather than the volume of the entire must. Since we already did our calculations for lowering the ºBrix earlier, we can use our new juice volume with the correct brix level:
L1 = (27.12 gal of must) x (70% (Rhône grape) = ~19 gal (71.9 liters.)
So, for our 27 gal of must, we are going to look at acidulating 19 gal (71.9 liters) of juiceby 2.0 g/L TA (0.2%)
Since: 3.8 grams Tartaric Acid per US Gallon raises TA by + 1 g/L (or .1%)
Then, we can just do the following calculations to determine how much Tartaric Acid will be needed:
Gallons: (19 gal) x (7.6 grams, from: 2 x 3.8 grams per gallon) = 144.4 grams
Liters: (66.3 liters) x (2 grams per liter for .2% TA) = 143.8 grams
If you don’t have a scale:
1 level teaspoon Tartaric Acid per US Gallon raises TA by +1.2 g/L (0.12%)
1 tsp Tartaric acid = 5 grams.
-Dilute the addition in just enough warm water to dissolve the crystals completely. Add a portion to the must. Mix thoroughly, test and taste. Add the rest if needed.
In the end, to correct our must starting at 27.5ºBrix with a pH of 3.95 and a TA of .5, we added 8.05 liters of water acidulated to 6.0 g/L TA (with 48.3 grams of Tartaric Acid). This brought the ºBrix to around 24.5º without changing the TA or pH of the must.
With the dilution was finished, we were able to hone in on the pH and TA. Because of the inexact nature of TA and pH adjustments, we saw a combination of the "art and science" of winemaking. Sugar dilution techniques are relatively straightforward and easy to predict. TA/pH adjustment involves a number of factors, ranging from unpredictable end results to judgment calls regarding the size of acid additions. We didn't make the full "on paper" addition of the quantity needed (+4.5 g/L% TA or 0.45%), which may have been too extreme. The actual ending amount of acid used (+ 2.0 g/L TA, or 0.2%), was a safe compromise that placed both the pH and the TA within acceptable ranges and was verified by taste. More can be added later if needed.
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