The ash content is defined to be all those products remaining after igniting the residue left from evaporation of the wine. The ignition is carried out in such a way that all the cations (excluding the ammonium cation) are converted into carbonates or other anhydrous inorganic salts.
The wine extract is ignited at a temperature between 500 and 550 °C until complete combustion (oxidation) of organic material has been achieved.
Pipette 20 ml of wine into the previously tared platinum dish (original weight P° g). Evaporate on the boiling water-bath, and heat the residue on the hot-plate at 200 °C or under the infra-red evaporator until carbonization begins. When no more fumes are produced, place the dish in the electric muffle furnace maintained at 525 ± 25 °C. After 15 minutes of carbonization, remove the dish from the furnace, add 5 ml of distilled water, evaporate on the water-bath or under the infra-red evaporator, and again heat the residue to 525 °C for 10 minutes.
If combustion (oxidation) of the carbonized particles is not complete, repeat the operations of washing the carbonized particles, evaporation of water and ignition.
For wines with a high sugar content, it is advantageous to add a few drops of pure vegetable oil to the extract before the first ashing to prevent excessive foaming.
After cooling in the desiccator, the dish is weighed (P 1 g).
The weight of the ash in the sample (20 ml) is then P = (P 1 − P o) g.
The weight P of the ash in grams per litre will be given to two decimal places by the expression: P = 50p