What Is a Hydrometer?

A hydrometer is a tool used for determining the relative density of a liquid. Hydrometers are normally graduated and calibrated with single or multiple scales such as API Gravity and Specific Gravity.

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Hydrometer alcohol

A hydrometer allows home distillers to determine the amount of sugar in their wort. For example, beer hydrometers are basically used to measure the amount of sugar present in a liquid.

A hydrometer typically consists of a hollow glass tube with a larger bottom for buoyancy; mercury or a ballast like lead for stability; and a thin stem with constantly-spaced graduations for measurement. The liquid to be measured is poured into a sizeable container, usually a graduated cylinder, and a hydrometer is slowly immersed into the liquid until it is freely floating. The position at which the liquid surface is in contact with the stem of the inserted hydrometer indicates relative density.

Hydrometer reading

Hydrometers are typically calibrated for various uses, e.g. an alcoholometer for determining higher volumes of alcohol in spirits, a lactometer for determining the density of milk, or a saccharometer for gauging how much sugar is in a liquid.

When it comes to home brewers, using the hydrometer to take measurement both at the start and the end of the fermentation process allows one to test and measure which scales specific gravity of the alcohol content in the final product and to evaluate the performance of yeast used.
What Does The Hydrometer Do?

A hydrometer can be found in any beer or wine making environment.

It determines the Specific Gravity of the liquid that you want to ferment and this should then give you an idea of the Alcohol by Volume (ABV) you’ll end up with.

The hydrometer is then used throughout the fermentation process to ensure sugar is completely converted to alcohol. You’ll be able to realize this by the reduction in gravity via temperature controllers. The gravity will drop as more and more sugar is converted into alcohol.

For instance, the initial gravity in a regular wine ranges from 1.075 to 1.090. This figure will change each day by around 10 points depending on factors such as nutrition and temperature. After several days, this figure will drop to, let say, 1.040 and eventually settle in the range of 1.000 to 0.990.

How Does a Hydrometer Work?

As we’ve mentioned above, it helps to measure sugar content in a liquid. The gravity reading is higher when there is more sugar in the liquid. In contrast, the reading is lower when there is more alcohol present in the liquid (i.e. after fermentation since the sugar has been converted to alcohol).

For instance, when the hydrometer is immersed in water at room temperature, the reading will settle at 1.000. This is very important to know since it can help you test the accuracy of your hydrometer.

Basically, the denser the liquid (due to more sugar content), the higher the reading.

How to Use a Hydrometer

Your hydrometer has been purposely designed for the home beer and wine maker. It features a reasonably wide range, thereby eliminating the need for multiple tools of narrower ranges that would otherwise be required to get the job done.

As mentioned earlier, a hydrometer helps to measure the density of a liquid relative to water. Water is assigned the value 1.000, and all of the other liquids are measured in relation to this value.

The result is the Specific Gravity of the liquid in question. As you add honey, sugar, molasses, malt extract or any other soluble solid, the figures after the decimal point will typically increase. During fermentation, sugar is converted into alcohol and carbon dioxide. The figure will, therefore, decrease.


Simply add the sample to your sample holder (hydrometer jar). It is important to ensure the temperature is in the suggested range based on your particular hydrometer. Be sure to utilize enough of the sample to ensure your hydrometers measure properly and doesn’t reach the bottom of the holder.
Slowly put the hydrometer in the liquid to avoid overflow and allow it to rest. Make sure your hydrometer does not rest on the sides of the brewing equipment sample holder or it will give the wrong reading.
The point where the liquid meets the scale will be your reading. Make sure you take the reading below the meniscus (i.e. below the surface of the liquid).

Measuring Alcohol Content with a Hydrometer

You can also use your alcohol hydrometers to determine the alcohol content of your homemade beers wines or beverage.

Firstly, take a reading before fermentation. The hydrometer must have a scale known as the “potential alcohol” scale. The scale helps to measure specific amount of alcohol to be produced if the wash is fully fermented (S.G. 1.000 or less). To get the first reading, you can use a bear thief to extract a sample and transfer it to a sample cylinder. The testing cylinder must have enough liquid in it to properly suspend your hydrometer. Next, immerse the hydrometer and let it float. Wait until all the air escapes from your liquid. Then, make sure your hydrometer is at the middle and positioned vertically so you can get the most accurate reading. For a typical wort, the first reading will range from 1.035 to 1.060.

Once the fermentation is complete, take your second reading. From there, subtract the second reading from the first reading. The difference between the two figures is the alcohol content that you’ve been able to produce. To get you a rough idea of what you should aim for, a regular beer’s Final Gravity Reading (FG) is anywhere between 1.015 and 1.005.
We not only supply specific gravity hydrometers, we supply a wide variety laboratory equipment and brewing supply such as drip trays, pressure gauges, heating and cooling towers, test kit. Browse our online store of call us to help you select your brewing equipment to complete brewing system.

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