Home Wine Making - How To Read A Hydrometer

Published: 14th June 2011
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As a beginner wine maker, you will frequently stumble upon wine-making instructions or guides that involves the use of a hydrometer. This piece of equipment will most likely confuse you as there is a high chance that you've never been aware of such device before - not to mention understanding how to make use of it!

For starters, we will explore the purpose. Exactly why do you need to have a hydrometer in wine making? The hydrometer will allow the wine maker to check the alcohol level in the wine. It measures the specific gravity of a liquid and by subtracting this reading pre and post fermentation, wine makers will be able to calculate the alcohol level in the wine they are making.

Before we move on to reading the hydrometer, there is another significant concept to clear up - the specific gravity. Specific gravity is a ratio of the density of a substance to that of water. And so, the specific gravity of water is going to be equal to 1.00 and specific gravity of fruit juice used for wine-making are usually more than 1.00 (around 1.07 to 1.09). The reason behind 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 much less dense than water.

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

We will now look at how you will use as well as read a hydrometer. To start with, you need to pour some of the fruit juice into the hydrometer and ensure the bulb is floating without touching the base. Read off the scale. The reading should be around 1.07 to 1.09. In addition, the hydrometer ought to come with its own temperature correction table and so, you need to check the temperature of the fruit juice 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 will likely be less than 1.00. Otherwise, you will have to give the wine some more time to keep on fermenting.

In order to approximate 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 hydrometer reading of the wine (previously fruit juice) is 0.98. Subtracting 0.98 from 1.08 gives you 0.1 and multiplying that by 125 gives you 12.5% - the estimated alcohol level. For wine, the approximate range of alcohol level is 12.5% to 14.5%.

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