If you want to know just how alcoholic your brews are, then you need to have a hydrometer. A hydrometer measures sugar gravity. (You can buy one in Woolworths) You use a hydrometer first of all when you have your brew in a bucket, and when it is cool, but BEFORE you add the nutrient and yeast.
In the beginning, the sugar gravity is high. As the yeast ferments the ingredients, it uses up sugar, and produces alcohol and carbon dioxide. Carbon dioxide bubbles up through the fermentation lock, alcohol stays in the liquid.
Wine finishes fermentation either when the yeast has run out of sugar (runs out of food) or when the alcohol level gets above 16.5%, which then kills the yeast. The first situation results in a dry wine, the second in a sweet wine.
You use the hydrometer again, now in the fermenting bottle, when fermentation has ceased..
Here is an example.
1. Float the hydrometer in the bucket and make a note of the level at which it floats, eg 1080.(value A)
2. When fermentation has finished, float the hydrometer again. It should read 990.(value B)
To work out the alcohol level, subtract B from A. This gives value C. (eg 1080 – 990 = 90)
Then divide C by 7.36. This gives the percentage value of alcohol. (eg 90 / 7.36 = 12.2)
A wine with an original sugar gravity of 1080 and a final sugar gravity of 990 has 12.2% alcohol.