Some notes on sulfites, pH and TA

Since harvest is again upon us all, we at Vinmetrica thought it would be a good time to share a few tips on measuring and adjusting the three key parameters you need as fermentation begins and shortly after: pH, TA and free SO₂.

First, just a reminder that we have lots of information on our web site (www.vinmetrica.com).  You might want to browse through our Support section on the home page.  There you can find useful resources like videos, the latest version of the manual for your instrument, and our troubleshooting guide.

Second, we recommend you look through the latest version of your manual to refresh your memory as needed!

Measuring and adjusting pH and TA

Measuring pH is technically simple.  You calibrate your pH electrode, then insert it into the wine sample, let it equilibrate a few seconds and take the reading.  Here are some tips to keep it from going awry.

1. Calibrate at least once each day of use. Follow your manual’s instructions using current pH 7.00 and 4.00 calibration reference solutions (you can also use 7 and 3, or 4 and 3 reference solutions if you want). Note that in our latest manuals, we now recommend NOT stirring or swirling the solutions during calibration and measurement; just insert the electrode with a brief swirl and let it sit.
2. It’s a good idea to recheck the calibration a second time, and perhaps once later in the day, in case there’s any drift. Also, you can use saturated cream of tartar as a check on your calibration.
3. Refer to the pH troubleshooting section of our website if you encounter difficulty calibrating.

Measuring TA is done by titrating quantitatively.  Measure out 5.0 mL of wine, add some DI water, then monitor the pH as you slowly add measured amounts of a TA Titrant (ours is 0.133 N NaOH).  When the pH hits 8.2, stop and determine the total amount of TA Titrant added, from which you calculate the TA value.  Some tips here:

1. Sample preparation: centrifuge, filter or decant the sample to remove gross particulates. If there’s any appreciable dissolved CO₂ (like in fermenting samples), follow the manual’s instruction to discharge it.
2. Avoid titration errors: make sure there are no bubbles in your syringe or burette; these can dislodge, causing erroneous readings. Make sure you correctly read the starting and ending values on the syringe or burette. Try to hit the pH 8.2 endpoint with a single drop or less of the Titrant – slow down the rate of titration when the pH rises to 7.0.

Adjusting pH and TA should be done carefully – remember, you can ruin a wine by over-adjusting, while you can always add more to an under-adjustment!   Go slow and recheck calculations. I recommend an online tool or app like FermCalc (see below) or similar to assist in calculations for wines.

1. If you want to acidify, i.e. lower the pH and raise TA, a rough rule of thumb is: pH decreases by 0.1 unit for every gram of tartaric acid added per liter, provided that the TA value is not already high. By definition, that addition raises TA by 1 g/L. I do recommend using tartaric acid and NOT an “acid blend”, but that is up to you; you can look on-line for alternatives. But do use a wine calculator!
2. If you want to deacidify, i.e. raise pH and lower TA, I recommend adding potassium bicarbonate. Again, there are various other agents you can use. But do use a wine calculator!
3. A really good idea is try any additions on a scaled-down sample. For example, if you have 5 gallons of wine, take out say, a half liter (measure this as accurately as possible, i.e. 500 mL).  Use a wine calculator to determine the needed additions on that 500 mL volume, make the additions, mix well and re-test pH/TA.  Once you get the result you want, scale that addition up to the whole 5 gal (19 liters).
4. Another good idea: when in doubt, adjust by adding half as much as you think you need, mix well, and test again.
5. Don’t forget to taste! In the end, that is as important as any number!

Measuring and adjusting free SO₂

”You can ruin what would have been a great wine if you don’t manage your free SO₂ “

-A sadder but wiser winemaker

The Vinmetrica method for measuring free SO₂ has been around for 12 years now (25 years if you count the prototypes I once used in my garage!).  We know it provides a reliable and accurate method for wine testing.

Here are a few tips on managing free SO₂ (once your fermentation is complete).

1. Your goal is to keep free SO₂ at the right level for your wine. This level differs between wines, depending mostly on two things: a) whether it’s a white or a red, and b) the pH of the wine. This leads to the next tip:
2. Use a sulfite calculator! If you aren’t, you’re needlessly risking all your hard work! You simply put in your wine’s type (white or red), pH, current free SO₂ level, volume of wine, and what kind of sulfite you are using (I recommend 10% KMBS). The calculator then tells you how much sulfite to add. Here are some links to calculators that are free on line:

FermCalc

Winemaker Magazine’s Sulfite Calculator

Daniel Pambianchi’s Home Winemaking Website

3. Sulfite levels always drop, sometimes fast! If your wine sits around at levels of SO₂ that are too low, you’re again needlessly risking all your hard work!

When you first add sulfite at the end of fermentation, you should test SO₂ levels within 24 hours of any additions.  Let’s say your sulfite calculator told you to add sulfite to get to 30 ppm, and you’re currently at 0 ppm.  So you added 10 mL of 10% KMBS to your 5 gallons of red wine (whose pH is, let’s say, 3.58), according to the calculator, to achieve the desired 30 ppm (which BTW, gives a molecular SO₂ level of 0.5 ppm). Now, 24 hours later, you measure 6 ppm. This drop from the expected value is very common! Don’t be complacent! Add more sulfite and re-test!

Later, as you continue to adjust and measure SO₂, you’ll find that you can test and adjust monthly. But levels always drop, so be vigilant!

4. Common errors with Vinmetrica equipment (See our troubleshooting guide, as described above for a step-by-step aid.)
5. Just 1 drop of SO₂ Titrant causes the endpoint to occur. Something must be wrong!

Nope! You have zero free SO₂!

1. I added 5 mL of Titrant and no endpoint was seen.

This suggests you have more than 100 ppm free SO2, or perhaps an instrument/procedure error, or some kind of interference – Follow the troubleshooting guide to figure out which.

 

Contact us at info@vinmetrica.com if you have questions or comments.