Recueil des Méthodes d’Analyse des Vinaigres de vins

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Determination of the fixed acidity content (Type II)

OIV-MA-VI-02 Determination of the fixed acidity content

Type II method

  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.

  1. 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.

  1. 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.

  1. Equipment and utensils

Standard laboratory equipment including:

4.1.         Water bath at 100 °C

4.2.         200 ml capacity porcelain capsules.

  1. Preparation of sample

Homogenize the sample by stirring and filter if necessary.

  1. 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.

  1. 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.
    1.          Presentation

Round off the results expressed in grams of acetic acid by L, to the nearest decimal.

  1. 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

  1. 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.