WINE IS ACIDIFIED WITH TARTARIC ACID ( APPROXIMATELY 0.5 G FOR EACH 20 ML ) PRIOR TO STEAM DISTILLATION . PRECAUTIONS MUST BE TAKEN TO AVOID THE CARBON DIOXIDE IN THE DISTILLATE . THE INDICATOR USED IS PHENOLPHTHALEIN . THE ACIDITY OF DISTILLED FREE AND COMBINED SULPHUR DIOXIDE IS NOT CALCULATED AS VOLATILE ACIDITY AND SHOULD BE DEDUCTED FROM THE ACIDITY OF THE DISTILLATE AS WELL AS ANY ACIDITY FROM SORBIC ACID .
9.3 . EXPRESSION OF RESULTS
THE VOLATILE ACIDITY IS EXPRESSED IN MILLIEQUIVALENTS PER LITRE AND IS DETERMINED TO THE NEAREST 0.5 MILLIEQUIVALENT .
9.4 . SINGLE REFEREE AND USUAL METHOD
PRINCIPLE OF THE APPARATUS AND ITS CONTROL
THE APPARATUS CONSISTS OF A STEAM GENERATOR , A BUBBLER INTO WHICH THE WINE SAMPLE IS PLACED , A RECTIFYING COLUMN AND A CONDENSER .
IN VIEW OF THE LARGE VARIETY AND TYPE OF EQUIPMENT WHICH HAVE BEEN OR WHICH COULD BE PROPOSED , AND IN VIEW OF THE DIFFICULTIES WHICH THE ADOPTION OF A SINGLE TYPE OF EQUIPMENT FOR ALL USERS IN EVERY COUNTRY WOULD PRESENT , IT IS PREFERABLE AND RATIONAL TO SPECIFY IN THE FOLLOWING MANNER THE MINIMUM CONDITIONS WHICH MUST BE MET BY ANY EQUIPMENT OR PROCEDURE PERMITTING THE ACCURATE DETERMINATION OF VOLATILE ACIDITY AS DEFINED :
1 . THE STEAM PRODUCED BY THE GENERATOR MUST BE SUFFICIENTLY FREE OF CARBON DIOXIDE SUCH THAT 250 ML OF DISTILLATE TO WHICH HAS BEEN ADDED 0.1 ML OF N/10 SODIUM HYDROXIDE AND TWO DROPS OF PHENOLPHTHALEIN ( 1 : 100 ) EXHIBITS A STABLE COLORATION FOR AT LEAST 10 SECONDS .
2 . UNDER NORMAL CONDITIONS OF USE , THE RECOVERY OF AN AQUEOUS SOLUTION ACETIC ACID PLACED INTO THE BUBBLER INSTEAD OF WINE SHOULD BE AT LEAST 99.5 % IN THE DISTILLATE .
3 . NOT MORE THAN 5 % OF LACTIC ACID , ADDED AS A NORMAL SOLUTION TO REPLACE THE WINE IN A SIMILAR CONTROL EXPERIMENT , SHOULD APPEAR IN THE DISTILLATE UNDER THE CONDITIONS WHICH PRODUCE A 99.5 % RECOVERY OF ACETIC ACID .
ANY APPARATUS AND PROCEDURE WHICH PERMITS THESE THREE TESTS TO BE CARRIED OUT SUCCESSIVELY AND SUCCESSFULLY FULFILS THE REQUIREMENTS OF OFFICIAL INTERNATIONAL EQUIPMENT AND PROCEDURE .
THE TWO TYPES OF APPARATUS DESCRIBED BELOW MEET THE SPECIFIED CONDITIONS : THE FIRST IS SUITABLE FOR LABORATORIES DEALING WITH LIMITED NUMBERS OF SAMPLES , THE SECOND IS INTENDED FOR LABORATORIES WHERE A LARGE NUMBER OF DETERMINATIONS OF VOLATILE ACIDITY HAVE TO BE CARRIED OUT DAILY AND AS QUICKLY AS POSSIBLE .
1 . SMALL APPARATUS
STEAM IS PRODUCED IN A 1 500 ML FLASK . THE BUBBLER CONSISTS OF A CYLINDRICAL TUBE OF 3 CM DIAMETER AND 27 CM HEIGHT . THIS TUBE IS HEATED EITHER ELECTRICALLY OR BY A FLAME ; THE BASE OF THE BUBBLER TUBE IS INSERTED IN THE 29 MM DIAMETER HOLE CUT IN A SHEET-METAL DISC OF 15 CM DIAMETER AND UNDER WHICH THE FLAME IS PLAYED . THIS PREVENTS ANY OVERHEATING OF EXTRACTIVE MATERIAL IN THE WINE