As a beginner wine maker, you will often come across wine making instructions or guides that calls for the use of a hydrometer. This piece of equipment will most probably confuse you as there is a high chance that you have never heard of such equipment before – not to mention knowing how to use it!

For starters, let us first explore the purpose. Why do you need a hydrometer in wine making? The hydrometer allows the wine maker to check the alcohol level in the wine. It measures the specific gravity of a liquid and by subtracting this reading before and after fermentation, wine makers will be able to estimate the alcohol level of the wine they are making.

Before we proceed on to reading the hydrometer, there is another important concept to clear up – the specific gravity. Specific gravity is the ratio of the density of a substance to that of water. Thus, the specific gravity of water will be equal to 1.00 and specific gravity of fruit juice used in wine making will often be higher than 1.00 (around 1.07 to 1.09). The reason for the higher specific gravity is because fruit juice contains sugar and other substance added to it which makes it much denser than pure water. The specific gravity of alcohol is 0.787 which means it’s less dense than water.

With the above concept in mind, it becomes clear how wine makers estimate the alcohol level. During fermentation, sugar (heavier than water) in the fruit juice is converted into alcohol (lighter than water). Thus, the specific gravity of fruit juice will fall during fermentation, and once this value stop decreasing, you know that fermentation has ended and all the sugar has been converted into alcohol.

Let us now explore how you will use and read a hydrometer. First, you will need to pour some of the fruit juice into the hydrometer and ensure that the bulb is floating and not touching the base. Read off the scale. The reading should be around 1.07 to 1.09. In addition, the hydrometer should also come with its own temperature correction chart and thus, you will also need to measure the temperature of the liquid and apply the correction value to the reading.

After 2-3 weeks of fermentation, take another reading by repeating the same procedure. If fermentation proceeded smoothly, the specific gravity should be below 1.00. If not, you will need to give your wine more time to continue fermenting.

To estimate the alcohol level, subtract the final reading from the initial reading and multiply it by 125. For example, the initial reading of the fruit juice is 1.08 and the final reading of the wine (previously fruit juice) is 0.98. Subtracting 0.98 from 1.08 will give you 0.1 and multiplying that by 125 will give you 12.5% – which is the approximate alcohol level. For wine, the approximate range of alcohol level is 12.5% to 14.5%.