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De-gassing Grape Juice, Must and Wine
- Grape juice, must and wine may contain dissolved carbon dioxide (CO2) through CO2 being used as an inert gas cover or from the fermentation process.
- CO2 in solution exists as carbonic acid and will be included in titatable acidity or volatile acidity measurements.
- To prevent this, all samples will have to be de-gassed.
- This can be achieved -
- by the use of a water aspirator (vacuum pump) to apply a vacuum, to a stoppered, thick walled, conical filter flask (see diagram).
Approximately 100 ml of sample can be degassed using this apparatus.
The vacuum should be applied for a few minutes, while swirling the sample, until no further liberation of gas bubbles are apparent.
- by sparging (bubbling) nitrogen gas (N2) through the sample for approximately 5 minutes.
Note: this method can cause excessive frothing in some grape juice samples)
- by measuring the sample quantity required (normally 10ml), and diluting with approximately 100 ml of distilled water that has been adjusted to a pH of 8.35.
This prepartion is brought to the boil and on cooling titrated directly.
Note 1: boiling water cannot retain dissolved gasses.
Note 2: Loss of volume through boiling will not reduce the amount of acid contained in the volume of sample chosen.