Alcohol is formed from the fermentation of sugar.

These components must be in balance. 2.7 grammes of sugar gives a reading of 1 degree on the hydrometer in 1 litre of wine.

Measure the finished wine when it has cleared. With storage it will become about 2 degrees drier. A wine that has fermented too far is too dry and sugar must be added (chaptalisation).

Otherwise the balance, flavour and body will suffer. Flavour in a wine that is too dry can be good but is improved enormously by chaptalisation. The body, flavour, and nose (aroma) are enhanced.

When wine ferments out, becoming too dry, it has to be chaptalised.

Chaptalisation is calculated thus: the hydrometer reading of the wine to be sweetened minus 1000 x 2.7 grammes of sugar x litres wine = for example (a strong wine) 1020 hydrometer (specific gravity) degrees = 20 x 2,7 grammes sugar x 20 litres of wine = 1080 grammes of sugar. Grape juice makes chaptalising easy, particularly with light wines (3 millilitres/litre gives 1 hydrometer degree). 2 decilitres of grape juice does not affect the dryness but greatly improves the flavour and keeping quality of the wine.