TOTAL ACIDITY OPERATIONAL TECHNIQUE
It is a very fast and comfortable method. It is such the methodical that it is used throughout winery for its ease.
In fact, it is an alkalimetry done directly on wine and, in many cases, if the wine is quiet, without the elimination of the present carbonic neither sulphurous. The alkaline solution is ready so that operating on 10,00 ml sample, each milliliter of reagent spent equals one gram of acidity, expressed in sulphuric acid.
1. Put in a glass of 100 ml. 10,00 ml of wine sample or grape juice, measured with a pipette clean and dry, or washed in the wine itself.
2. If the wine is white add two or three drops of phenolphthalein. If the wine is red, there is no need to add indicator.
3. Pour, drop by drop, the solution of NaOH TOTAL ACIDITY
4. Final turn will be noticed when touching with a PH indicator paper, leaving adding reactive when such paper indicates pH 7.
The number of milliliters tenths of reagent spent indicates the number of grams and tenths of TOTAL ACIDITY expressed in sulphuric acid.
If you want to express the acidity found in ac. tartaric, multiply the amount spent by 1.53 . If the value wishes to be expressed in miliequivalents / liter, sulphuric acid is multiplied by 20.4 .
A) In some white wines, is not detected much the pink colour when using the phenolphthalein. It is preferable to control the endpoint of the neutralization with the help of indicator paper, or pH meter.
B) The immersion of these reactive roles in wine, must not be instantaneous, near the end of the operation, requiring stay in wine 10 or 20 seconds.