How To Use a Hydrometer 

Review Of The Hydrometer

First, let’s review the hydrometer. The hydrometer is a glass bulb that is weighted and floats in a testing jar. The hydrometer will tell you how much alcohol was made in the fermentation process. The scale on the Mile Hi Distilling hydrometers is called a triple scale which gives you three scales. A brix reading, a specific gravity reading, and an approximate potential alcohol reading.

A hydrometer measures the density of a liquid in relation to water. In the case of distilling, we are measuring the amount of dissolved sugars in the wash or mash compared to water. Pure water has a specific gravity of 1.000 and as sugars are dissolved into solution it will cause the gravity to increase. So why do we need to use a hydrometer? A hydrometer gives you the answer to how much alcohol did my fermentation produce which is important to know.

If your fermentation did not work well and you did not create much alcohol then you need to know so you can fix the problem. If you don’t create the alcohol in the fermentation process then there will be nothing to distill out except for water. The old saying of “what you put in is what you get out” means a lot in this scenario.

The Three Scales On The Hydrometer

Brix Reading

We suggest learning about Brix later. Mostly more advanced brewers will use a Brix reading. Keep it simple for now.

The Approximate Potential Alcohol Reading

This a good quick look at how much alcohol you will potentially produce if everything goes right in the fermentation process. FYI – the most alcohol you can create in fermentation is around 20%. What happens is when the alcohol gets around 20% the yeast cells die off and stop producing more alcohol.

Specific Gravity Reading

Using this specific gravity reading when using a hydrometer is a solid way to know how much alcohol was produced in fermentation. In order to accomplish this, you get a reading right at the start before you add yeast and you get another reading at the end of fermentation.

Use a simple math formulation and then you know how much alcohol was created during fermentation so ultimately you have an idea of how much alcohol there is to distill out of a still. This gives you an estimate. You won’t get every dropout and you will be removing forshots, heads, and tails when you make your cuts.

A rough estimate would be you should be able to yield about half of this number. See below step by step how to use a hydrometer using the specific gravity reading.

Steps To Use a Hydrometer

Step 1.

After the sugar water, mash, or wash has cooled to 70F to 80F and before you add the yeast fill up about 3/4 of your test jar (the plastic or glass test jar to float the hydrometer).  Float your hydrometer and write down the reading you get. This is the initial specific gravity or original specific gravity or called OG original gravity.

Step 2.

Ferment for 5-7 days (fermentation times depends on what your fermenting) then check the specific gravity again which is now called the Final specific gravity or FG final gravity.
Hydrometer Step by Step Instructions

Step 3.

Now we need to do a little math so grab your calculator and complete the formula below:
OG (original gravity so the reading that you started with) – FG (final gravity so the reading that you ended with)
Take this number and multiply it by 131.25 to get your percentage of alcohol in your fermentation.

For Example:

OG (original specific gravity) of 1.080 – FG (final specific gravity) of 1.003 = .077 x 131.25 = 10.106% alcohol by volume (ABV)

So this example is telling us that there is a little over 10% alcohol made in this fermentation.

*Note:  Hydrometers can be used when fermenting grains, fruit, molasses, agave, etc.  There are temperature correction charts online if you want to get extremely accurate. For example if you check your wash at 70F compared to checking your wash at 75F there is would be about ½ percent correction.

Difference Between an Alcohol Meter and a Hydrometer

An alcohol meter is the tool to use to test the alcohol percentage or proof of the distilled spirit. This alcoholmeter or alcohol meter can be floated in a distillers parrot to give you real time alcohol percentage or proof of spirts coming off the still.
The hydrometer is used to tell you the ABV ( alcohol by volume ) in the fermentation process so really it tells you how much alcohol was made when fermentation is complete.  This will give you an idea of how much alcohol you can distill out of your still. There are variables like how much of the foreshots and heads you took out and how far ran into your tails. See making cuts.