Acid Adjustment

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Jul 10, 2018
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I have had trouble with acid adjustments in the past. I changed my process in 2019 and I’m happy with the results. Here’s what I did.

Day 1: On crush day, I added Lallzyme EX-V enzyme to help break down the must.

Day 2: The following day, I tested the acid and made adjustments to the must.

1. I prepared a must sample according to the “MoreWine! Guide to Red Winemaking” [1]. Basically, I just “lightly blended” a must sample, strained it, and put it through a coffee filter to get clear juice. The enzyme addition and the blending helped to break down the grapes to give a more representative sample for testing.

2. I used part of the clear sample to test pH and TA.

3. I determined the amount of tartaric acid to add based on a process described by the British Columbia Amateur Winemakers Association [2]. I prepared a 10% tartaric acid solution (10g of tartaric acid in 100ml of distilled water). To make this, I dissolved 10g of tartaric acid in a small amount of distilled water, say 50ml, then I added distilled water to exactly 100ml. I filled a syringe with a known amount of the 10% solution, say 10ml. Next, I put 100ml of the clear must sample in a beaker. While measuring the pH with my meter, I added the 10% solution to the must sample until I reached my desired pH level. For each 1ml I added to my sample, I needed to add 1g of tartaric to each liter of the finished wine volume. It’s important to note that acid additions are not based on must volume, but the expected finished wine volume [1].

Using the 10% tartaric acid solution made determining my acid adjustment easy. Getting the clear sample was time consuming, so I only used 50ml, instead of 100ml to calculate my adjustment. Decreasing the volume of the sample by half required that I add 2g of tartaric per liter for every 1ml of 10% solution I added. I added the full amount to my must and didn’t look back.

This year I did not take TA into consideration when making my acid adjustment. My desired pH was 3.4 or less. That sounds aggressive, but I was following the recommendation of The Australian Wine Research Institute.

“Is it best to adjust acidity to a pH or titratable acidity value? Of course, one would hope that the pH can be adjusted to the desired value and at the same time achieve the desired TA value. However, if the desired values of both parameters cannot be achieved, then preference should be given to the pH, particularly with musts. This is because pH plays an important role in many aspects of winemaking and wine stability. The pH influences microbiological stability, affects the equilibrium of the tartrate salts, determines the effectiveness of sulfur dioxide and enzyme additions, influences the solubility of proteins and effectiveness of bentonite and affects red wine colour and oxidative and browning reactions (Boulton et al. 1996).

“It is best to adjust the acid as early as possible because juice and wine are more stable at lower pH. In the case of red musts, it is advisable to adjust the pH to 3.4 or lower. If the desirable TA cannot be achieved, then the must should be adjusted to pH 3.4 regardless of the amount of tartaric acid required to do so. Note that a large amount of the added acid will precipitate later as KHT, resulting in a decrease in the TA. Given that the pH of red wines is likely to rise during fermentation, due to the leaching of potassium ions from the skins, it is recommended that the pH be measured during fermentation on skins and that additions be made to maintain the pH in the range 3.4 – 3.5.”

My 2019 grapes were Sangiovese, Cabernet Sauvignon, and Cabernet Franc from Lodi.

Sangiovese: pH 3.57, TA <5, added 1.2g tartaric acid per liter finished wine, pH today is 3.38
Cabernet Sauvignon: pH 3.72, TA 4.25, added 2.4g tartaric acid per liter finished wine, pH today is 3.42
Cabernet Franc: pH 3.62, TA 5.1, added 1.4g tartaric acid per liter finished wine, pH today is 3.48

They still have some residual CO2, so I expect the pH will rise a little bit.

Those are the numbers, but the bottom line is how it tastes. Right now, I wouldn’t change a thing. I’m happy with how they are coming along.