Recently I compared four methods for testing acid content of wine. They are, from left to right, acid titration with sodium hydroxide, “Precision” pH control paper, colorpHast pH-indicator strips and Vinoferm acidometer.

The purpose of the testing was to determine a fast, easy and accurate way to determine the acid content of wine.

ACID TITRATION KIT – This appears to be the most widely used method of wine acid testing. A specific volume of the wine is put into a clear container, 3-4 drops of a “color indicating solution” is put into the wine and then sodium hydroxide is put in drop by drop until a color change is noted. Each 1 cc of sodium hydroxide needed to effect a color change indicates .1% acid content as tartaric. This is the method I used for the first 2 years I made wine. It was very easy to use with lighter colored wines, and very difficult with the darker wines. I would test and adjust acid before fermentation. Re-test and adjust again about 4 months before bottling. Each new bottle of sodium hydroxide would last me about 6-8 months and I would be able to test several different batches of wine. Some only once with a new bottle, some twice. I began to notice my testing would sometimes fluctuate wildly and I didn’t know why. Sometimes the first test would give a reading of .450%T. I would then calculate and adjust by adding acid to the desired .700%T. The next reading, several months later, would give a reading of .850%T or higher. Then acid content would have to be reduced. Sometimes the reading worked out exactly as planned. Then, one time I tested a wine, wrote down the results to add acid at a later time and forgotten I had already tested the wine. A week later I bought a new bottle of sodium hydroxide and re-tested the wine in order to add any necessary acid blend. When I went to write down the results I discovered the “new” test was .275%T lower than the test I did 1 week earlier. I purchased another bottle of sodium hydroxide from a different source. That test was .350%T lower than the original test. The sodium hydroxide and/or the color indicating solution appears to deteriorate over time. I had no idea if my supplier had stored these chemicals for 2 months or 2 years before I purchased them. There was no bottling or expiration date on the containers. I then stopped using this method for my wine acid testing and started searching for something better. Comparison results have not been included in the chart because of this variable.

COLORpHAST pH-NDICATING STRIP AND “PRECISION” pH CONTROL PAPERS – The pH control papers are relatively inexpensive (about $5.00 for 100 strips) and appear to be very stable. A drop of wine is put on a strip and it changes color to indicate the pH. This must then be converted into %T. This sounds simple except for the fact that the color comparison blocks on my bottle of strips was so poorly printed that it was very difficult for me to determine what the color had actually changed to. After “playing” a little I found that letting the sample test spot dry for a bit (not completely dry) the color could be matched a bit better.

The range of the color comparison blocks was, on average .2 pH. Colors were sometimes not easy to compare because of lighting. Fluorescent, incandescent, sunlight (direct and indirect) all played a factor in determining the perceived pH. This explains why there is sometimes variances in the chart. The colorpHast strips are a bit more expensive (about $10.00 for 100 strips). The color change is much more noticeable because the printing is much better. However the range of the color comparison blocks was on average .3 pH. This is a bit wide for what I wanted them for but these were the best I could find at the time. The pH color (the actual reading) can only be interpreted as closely as what you (as the tester) determines it to be. Just like the “Control Papers”, a drop of the wine is put on the indicating strip and the resulting color indicates the pH. This test is best done and read with the strip wet. I purchased these strips from SanitationTools.com.

VINEFORM ACIDOMETER- This type of wine acid testing appears to be very accurate but very time consuming. I consider it the best method I have found to determine the acid content of a wine. The cost is considerably higher than any other type of testing kit I have found, about $21.00. A specific amount of wine is put into a graduated cylinder. Then several cc (or ml) of a blue indicator vinoferm is added to the wine. Continue adding the supplied solution until the color of the wine changes from dark green to (not quite) blue. The cylinder is graduated to indicate the % tartaric. At this point a drop of the tested wine is put on a litmus test paper. If (when almost dry) the test area turns red, the test liquid is too acid and more blue indicator must be added

When the color of the test strip remains the same, the -measurement is the correct % Tartaric. If the color turns blue-violet, the test is too alkaline and the test has to be started again. This test proved to be very time consuming, gradually increasing the indicating solution and testing each time. Dark colored wines are once again very hard to determine a change.

The chart at the left shows the result of testing each wine with a pH strip and a COLORpHAST strip. This gives me a point to start testing with the Acidometer which will give a correct reading without starting at the lowest level and testing every few drops.

Discrepancies between measurements of the pH strips and the COLORpHAST in relation to the acidometer reading can only be due to my misreading of colors in different lights. And due to the very slight changes of color that would indicate a pH change of + or - .3 pH.