Determination of the fixed acidity content (Type II)
Method OIV-MA-VI-02 : R2000
Type II method
Determination of the fixed acidity content in vinegars
(OENO 53/2000)
1. Definition
The fixed acidity of a vinegar refers to all the fixed (non-volatile) acids titled in the presence of phenolphthalein in an alcoholic solution, used as indicator.
2. Principle
Elimination of volatile substances from the vinegar by evaporation. Neutralization of the (non-volatile) acids of the residue in an aqueous solution using an alkali solution.
3. Reagents
3.1. Sodium hydroxide solution 0.1 M
3.2. Indicator - alcoholic solution of phenolphthalein at 1 g per 100 ml.
In a calibrated 100 ml flask, dissolve 1 g of phenolphthalein with a sufficient quality of ethanol at 95% (v/v) and bring up to the line.
4. Equipment and utensils
Standard laboratory equipment including:
4.1. Water bath at 100 °C
4.2. 200 ml capacity porcelain capsules.
5. Preparation of sample
Homogenize the sample by stirring and filter if necessary.
6. Technique
In a 200 ml porcelain capsule, add 10 ml of vinegar. In a water bath at 100 °C, evaporate until dry. Add 5 to 10 ml of water. Evaporate again until dry. Repeat this step five times, add approximately 180 ml of recently boiled and cooled water, add a few drops of indicator (3.2) and title with the sodium hydroxide solution (3.1) until a persistent pink color is obtained.
7. Results
7.1. Calculation
Considering:
- V to be the volume in ml of the sodium hydroxide solution using in titling.
The fixed acidity content expressed in grams of acetic acid per l of sample is given by
- 0.6 V.
7.2. Presentation
Round off the results expressed in grams of acetic acid by L, to the nearest decimal.
8. Interlaboratory validation (Hitos et al., 2000)
Units: % (m/V)
Sample | r | Sr | RSDr | R | SR | RSDR | RSDR
(Horwitz) |
Horrat
Index |
1 – 0.17% (m/v) | 1.0125 | 0.004 | 2.69 | 0.0428 | 0.015 | 9.18 | 5.22 | 1.76 |
2 – 0.17% (m/v) | 0.0103 | 0.004 | 2.19 | 0.0431 | 0.015 | 9.15 | 5.22 | 1.75 |
3 – 0.08% (m/v) | 0.0103 | 0.004 | 4.88 | 0.0201 | 0.007 | 9.57 | 5.85 | 1.64 |
4 – 0.07% (m/v) | 0.0083 | 0.003 | 4.20 | 0.0246 | 0.009 | 12.38 | 5.97 | 2.07 |
5 – 0.08% (m/v) | 0.0077 | 0.003 | 3.26 | 0.0285 | 0.010 | 12.11 | 5.85 | 2.07 |
9. Bibliography
- Anonymous, 1993, Métodos Oficiales de Análisis, Tomo II, Ministério de Agricultura, Pesca y Alimentación, Madrid, Spain.
- AOAC, 1984, Official Methods of the Ass. Offic. Agric. Chem., 14th edit., Arlington USA.
- Hitos P., Pons A., Martin de la Hinojosa, I, Gomez R., Hernandez A. and Muñoz J., 2000. Validation of analysis methods for total, fixed and volatile acidity of non-volatile reducing substances, copper and zinc in wine vinegars, Green Sheet of OIV No. 115.
- Llaguno C. et Polo M.G., 1991. El Vinagre de Vino, Consejo Superior de Investigaciones Cientificas, Madrid, Spain.