Determination of the Alcoholic Strength of Grape and Fruit Wines by Simple Analytical Methods

¹ Department of Applied Chemistry and Microbiology, Viikki B, FIN-00014 University of Helsinki, Finland
² Alcohol Control Laboratory (ACL), Alko Group Inc., P.O. Box 350, FIN-00101 Helsinki, Finland.

Different types of grape and fruit wines were analyzed for alcoholic strength. Alcoholic strength was determined by three different, simple methods: areometric, boiling point, and Rebelein's method. The areometric method proved to be the most reliable means of the three methods tested for determining the alcoholic strength of any type of wine. The observed alcohol contents by volume deviated by 0.0 to 0.8 percentage points from the reference values, and the correlation with the reference method was high (correlation coefficient, R = 0.98). The boiling point method was good for table wines (alcoholic strength 9% to 12.5% by volume). For sweet dessert wines, however, the deviation of the boiling point method was large (> 1 percentage point % vol). Because sugar content affects the boiling point of wine, the boiling point method cannot be used for sweet dessert wines without calibration and use of a quadratic equation. Rebelein's method was unreliable because of its poor repeatability. The difference between two parallel determinations of alcohol was up to one percentage point % vol, whereas for other methods the corresponding figure was 0 to 0.2% vol. The analytical differences were correlated vs. total acids, dry extract and sugar content in the samples tested. Correlations were poor except the correlation of analytical difference obtained with the boiling point method vs. sugar content or dry extract, in which cases the correlations were reasonable with R = 0.84 and 0.79, respectively.

Key words: wine, fruit wine, alcoholic strength, extract, areometer, boiling point

Submitted on January 8, 1996