Manuel Q. – NM
For those of you who have never used an acid test kit: basically what you are doing is taking a measured sample of wine and slowly adding sodium hydroxide to it until the wine permanently changes color. By knowing how much sodium hydroxide it took to get the color change, you can determine you wine’s acidity level.
An acid test kit can be a little awkward to use until you get the hang of it. I sometimes suggest to customers that they practice on some finished wine, first, before they actually need to use it. Here are some additional information for using an acid test kit. These are tips that go beyond the instructions you typically find with a titration kit.
- Run Through A Quick Test
When I’m using the acid test kit, the first thing I like to do is go through a test quickly. This is to establish “about” where the color change will occur. Then when doing a second test, I start off by adding enough sodium hydroxide to get close to the point of a color change. Then I add the sodium hydroxide one drop at a time. Adding the bulk of the sodium hydroxide all at once will save you a lot of time and aggravation in the long-run. With each drop you will want to shake the test-tube and see that either a magenta or grey color is dissolving completely away in the sample of wine. Streaks of either color are okay. They just need to be swirled out. It’s when the color stays permanently and alters the color of the entire sample. That’s when you want to take your measurement reading.
- Use A White Background
This tip for using an acid test kit is the one I think is the one that is most helpful. By holding the test tube up to a white background like a wall or sheet of paper you will be able to discern the color change more easily. You are essentially blocking out colors from the room, giving you a cleaner frame of reference when taking a titration of the wine.
- Use A Second Wine Sample For Comparison
Having a second test tube with another wine sample for comparison may be helpful. Put them side-by-side. Expect the color of the sample being tested to get lighter and lighter as more sodium hydroxide is added. That’s okay. You are not comparing the lightness or the darkness between the two wine samples. You are comparing the color hue of the two wine samples.
- Dilute The Wine’s Color
This tip for using an acid test kit does not apply to every wine. If the color of the wine is too opaque to see a color change, you can dilute it. Some red wines are just to dark for performing a titration. You can dilute it with distilled water. You do not want to use tap water or drinking water. Use distilled water, only. Dilute as much as you need to. This will not alter at what point the color change will occur or the math you use to calculate it.
- Make Sure The Wine Is Free Of CO2
The wine sample needs to be flat. You do not want CO2 (carbonation) from the fermentation to be in the wine sample. Carbon dioxide will throw off your reading. For this reason, the most opportune times to test your wine is before fermentation and before bottling. The wine must should be free of CO2 at both these times. If you are making your wine from fresh fruit, I would recommend testing at both times. The acidity level can change during a fermentation. The first test is to get the acidity close so that the fermentation can be healthy. Acidity plays a role in how well a yeast ferment. The test before bottling is to adjust for flavor – flat vs. tart flavors.
- Make Sure The Acid Test Kit Is Still Good
Here is the last tip for using an acid test kit. Both the activator and the reagent in your acid test kit will get old with time. This can throw off a titration reading – sometimes significantly. For this reason, it is not a bad idea to store these ingredients in the refrigerator for longer shelf-life. If you are not sure how old your acid test kit is, you can run a test on Welch’s grape juice – not from concentrate, straight Welch’s grape juice off the store shelf. It should have a reading of .67%-tartaric. If you get a reading that is higher than this, it means that your reagent (sodium hydroxide) is old and does not have its full strength.
Using an acid test kit is a great way for controlling your wine’s acidity. Hopefully these tips for using the acid test kit will help to make the process a little easier and an little more accurate.
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.