The test uses a sampler bulb to obtain a measured sample of must or wine.  The sample is either placed into a test tube and mixed or placed on the absorptive layer of the test strip.  After a prescribed waiting period, the color of test tube contents or the color in the viewing hole of test strip is compared to a provided color chart to determine test results.  One caution is that the results should not be determined under florescent light which creates a greenish tint that can affect color chart comparisons.

It has been my experience that there are some tests that are just more difficult with red wines.  This is because of the affect of the tannins and color pigments in the must or wine.  In the assembly of the test strip, Accuvin includes an interference removal layer.  The purpose of this layer is to absorb the tannins and color pigments and to reduce their impact on the test results.

I was unable to locate any information regarding the accuracy of the tests.  I am not a chemist and I do not have an extensive laboratory.  I use the tests and equipment generally available to the home winemaker.  In the remainder of this article I will attempt to get some feel as to the accuracy of the tests and whether I can use the Accuvin test instead of an existing test. 

My tests were conducted using the following wines:

Winexpert Limited Edition Gewurztraminer that had completed fermentation and before stabilization and fining

Commercial Italian Pinot Grigio

Mosti Mondiale fresh juice Carmenere must from Chile

Commercial California Merlot that had gone through malolactic fermentation

Winexpert Selection Merlot

Commercial California Cabernet Sauvignon

I did not perform all of the tests on all of the wines.

Free SO₂ test

My existing test to determine free sulfur dioxide (SO₂) is the Chemetrics Titrets.  From what I have read the Titrets tend to give a result that is approximately 10 to 20ppm too high.  The results are closer for whites than they are for reds because of the affect of tannin and color compounds in the red wine.  When I use Titrets, I subtract 10 from the white test result and 15 from the red test result and make sulfite additions based on these adjusted numbers.

Determining the end point in red musts or wines is extremely difficult with Titrets and I generally use dilution and a yellow light to detect the color change.  In comparing test results between the Chemetrics Titrets and the Accuvin free SO₂ test, I decided to use only the white wines. 

For the Gewurztraminer the Accuvin free SO₂ test results were 16ppm and Chemetrics was 22ppm.  For the Pinot Grigio the Accuvin results were 22ppm and the Chemetric results were 35ppm.  I tested the following two wines with the Accuvin but did not do a comparison Titrets test: the Commercial Merlot was 28ppm and the Carmenere must was 4ppm.

Titratable Acidity

I normally use the standard titration test using sodium hydroxide to determine titratable acidity.  Instead of using phenolphthalein to determine the end-point, I use a pH meter.  I do this to avoid the inevitable problem of determining the end-point with red musts or wines.  When the meter reads 8.2, I have just passed through the end point.  For my testing I used fresh buffer solutions to calibrate the pH meter and fresh sodium hydroxide.

The titration of the Gewurztraminer had a result of 0.63% while the Accuvin result was 0.80%.  The results for the Pinot Grigio were titration 0.51% and Accuvin 0.50%.  The Cabernet Sauvignon had titration results of 0.56% and Accuvin of 0.60%.  Finally, the Carmenere must had a titratable acidity of 0.83% per the titration method and 0.85% per the Accuvin test.

I do not know why there is such a significant difference in the results for the Gewurztraminer.  I did perform all of my analytical testing before I taste tested any of the selected wines.

pH Test

As far as my routine tests are concerned, this is pretty straight forward.  I use a pH meter that reads to two decimal places although for all of my adjustments I round to one decimal place.  The buffer solutions used to calibrate the meter were fresh.

The results for the Gewurztraminer were pH meter 3.1 and Accuvin 3.2.  For the Pinot Grigio both were 3.2 and for the Cabernet Sauvignon both were 3.6.  The Carmenere must had a pH meter reading of 3.6 and an Accuvin reading of 3.7.

Malic Acid and Lactic Acid

I have put these two tests together as I would only use them to determine the progress of malolactic fermentation.  Lactic acid is not produced by grapes; therefore, it would not be expected to be present in the must.  As malolactic fermentation progresses, one would expect to see the malic acid decrease and the lactic acid increase.

Since I do not have a wine going through malolactic fermentation, I cannot test the progress of decreasing malic acid and increasing lactic acid.  I did test the Carmenere must and Accuvin indicated that there was 300 mg/L of malic acid and less than 10 mg/L of lactic acid (less than 10 is the lowest reading on the color chart for this test).  The commercial Merlot I tested was selected because the Winemaker's notes indicated that it had undergone malolactic fermentation.  The Accuvin results for this wine were 160 mg/L of malic acid and 80mg/L of lactic acid.

Residual Sugar

I use the Clinitest or Dextrocheck method for determining residual sugar in the wine.  These kits were originally developed for diabetics to determine the amount of sugar in urine.  These tests give an indication of the amount of fermentable sugars (glucose and fructose) a well as the amount of non-fermentable sugars.

The Accuvin test measures only the fermentable sugars and therefore, one would expect the results to be lower than the Clinitest test results.  In testing the commercial Merlot, Clinitest indicated that there was 4 g/L of residual sugar while Accuvin indicated 1.5 g/L of residual sugar.  The Clinitest for the Pinot Grigo was 2 g/L of residual sugar and the Accuvin test indicated 750 mg/L.

I had read that "kit taste" may be the result of non-fermentable sugars giving the wine a taste described by some as similar to Jolly Ranchers.  I have a Merlot from a kit that I believe has this "kit taste" and I decided to test it.  The Clinitest results for this wine were 5 g/L of residual sugar and the Accuvin test indicated 1 g/L of residual sugar.  Although one test on one wine certainly isn't conclusive, this wine did have a lot of non-fermentable residual sugars.

The Bottom Line

For me the jury is still out on the accuracy of the tests.  I was unable to locate any information regarding accuracy and the few tests I performed certainly do not establish a level of accuracy.  I do not have access to an Aeration Oxidation setup for testing the accuracy of the Accuvin free SO2 test and I have no means to verify the accuracy of the results of the Malic and Lactic Acid tests.

The fact that these tests are quick and easy is certainly an advantage.  Additionally, an expiration date appears on the test package, which I find to be a positive feature.  With my other tests, I really have no easy method to determine whether the materials used in the test are outdated.  The cost per test is high and each home winemaker will need to consider whether it is justified in their operation.

Based on what testing I did perform and on the wines I selected for testing, the results were generally in the range of my expectations.  Although I don't know how precise the tests are, I do believe that they are accurate enough for the home winemaker to make decisions based on the results.