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Fall Bright, The Winemakers Shoppe, 10110 Hyatt Hill, Dundee, NY 14837 Acid testing is always more of a challenge than sugar testing. If you are color blind, you will have to have a pH meter to run your test or have someone else do it. We try to give the TA (total acid) numbers for our juices during the season. I post them online as we get them. Tom runs all of these tests. Retyped from Wine Analysis Bulletin, by Harold E Applegate, with permission from American Wine Society , 3006 Latta Rd, Rochester, NY 14612 585-225-7613 Total acidity as tartaric acid in must or wine: 1. Must or white wine: First clarify the must or wine by filtration through Whatman #1 filter paper or by centrifugation. The latter method is a fast and most efficient method for those who can afford a small clinical centrifuge. Add 5 ml of must or wine to 75 ml of boiling distilled water followed by 5 drops of phenolphthalein indicator. Agitate well and continuously. Titrate with N/10 NaOH to the faint pink endpoint stable for at least 1 minute. Volume of NaOH used X 0.15 = grams of acid/100 ml of must or wine. 2. Red Wine: Add 5 ml of red wine to 75 ml of boiling distilled water and with adding the indicator, titrate with N/10 NaOH until the solution is blue-green in color. Now add 5 drops of phenolphthalein indicator and complete the titration to the pink endpoint. The endpoint is very tricky and requires practice. One way to avoid the difficulty is to stir the red wine vigorously with a little bone charcoal and clarify as done initially. The resultant decolorized wine is then used as a white wine. Use the same equation that was used for white wine to calculate the result. (End of AWS excerpt) Tom Mitchell's Suggestions: For red wine (and white also) Tom will filter the juice or wine that he is taking the sample from through multiple layers of cheesecloth, drawing his 5 ml sample with a pipet or a syringe. He uses a graduated beaker or a white interior container for the test. The use of boiled or hot distilled water drives off any CO2 that may be in the wine/water. CO2 present in the sample will give a false reading. CO2 is less soluble in hot than cold and will go off. The amount of water for the test is not important. 75 ml is fine for a white wine test, but for a red wine he uses 150 ml of water to dilute the color. Very dark red wine is almost impossible to do without a pH meter. When doing a red test without a pH meter, he suggest titrating with N/10 NaOH until the solution is blue-green in color, then adding the 5 drops of phenolphthalein color indicator and completing the titration to the pink endpoint. A white background with a strong light helps with these tests. He uses the pH meter to determine the end point in red samples. If using a pH meter, color indicator is not even necessary. So he titrates and agitates the sample with the pH meter probe in it. The pH endpoint is 8.4. He then takes the reading of the amount of sodium hydroxide used to reach the end point and multiplies by 0.15. Actually he doesn't multiply, he has a chart he uses. It is available at the shop. Isn't that wonderful? Plus we have a magnetic stirrer and a self-leveling buret that we picked up used from a lab. These tools definitely make the task easier. To calculate the acid reading (tartaric) TA, multiply the amount of NaOH used by 0.15. This factor will give you the TA if you are using 0.1Normal Sodium hydroxide. Check your label. Sodium hydroxide also loses strength with age and should be replaced every 6 months. There is also a procedure for testing the strength of sodium hydroxide for the most accurate reading. Marcy Mitchell from Fall Bright, the Winemakers Shoppe, 10110 Hyatt Hill, Dundee, NY14837 |
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Fall Bright,
The Winemakers Shoppe Tom and Marcy Mitchell Thank you for visiting our web site! |