Velp Scientifica
– UDK139 Operating Manual
10004762/B5
107
35 - Method to determine the volatile acidity of wines
The volatile acidity is due to the acids belonging to the acetic series which are present in
the wines as free or salt forms.
The method is based on the titration of the volatile acids separated from the wine by a
steam distillation.
The wine to be analysed is previously freed from the carbon dioxide.
It is also necessary to subtract from the distillate acidity the acidity of the sulphur dioxide
free or combined which have been distilled.
It is also necessary to subtract the acidity due to the sorbic acid added in the wine. The
salicylic acid added in some countries before the analyses in order to stabilise the wines is
present , in some part, in the distillate. It is then necessary to dose it and subtract from the
volatile acidity.
Reagents
Crystallised tartaric acid (C
4
H
6
O
6
), analytical purity
solution 0.1M of sodium hydroxide (NaOH), analytical purity
solution of phenolpthalein 1% in neutral ethanol 96% vol.
hydrochloric acid (
20
= 1.18-1.19 g/ml), analytical purity, diluted 1/4 (v/v)
solution 0.005M of iodine (I
2
), analytical purity
crystallised potassium iodide (KI), analytical purity
starch-water 5g/l: dissolve 5g of starch in about 500ml of water.
Bring to boiling ,stir, and maintain 10 minutes; add 200g of sodium chloride.
After cooling down, bring the volume to 1l.
saturated solution of sodium tetra-borate (Na
2
B
4
O
7
-10 H
2
O),
analytical purity, about 55g/l at 20°C.
Procedure
1) Sample preparation: elimination of the carbon dioxide (CO
2
)
Bring the sample to room temperature. The dissolved carbon dioxide is removed by
stirring the sample or by using an ultra-sonic bath.
As an alternative: pour about 50ml of wine in a vacuum flask; stir and create vacuum at
the same time using a pump; stirring must take 1 or 2 minutes.
2) Distillation:
pour in a test tube 20ml of wine freed from the carbon dioxide.
Add about 0.5g of tartaric acid (used to make free the salified volatile acids which, in the
international methods, must be included in the volatile acidity) and place the test tube in its
site in the distillator.
Analytical parameters:
H
2
O = 0ml. NaOH = 0ml. H
3
BO
3
= 0ml.
Take off the tube used to collect the distillate from the end of the condenser and
place a new silicon tube.
Place in position on the round stand of the distillator an empty Erlenmeyer flask and
collect at least 250ml of distillate.
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