The Importance of Distilling Alcohol Hydrometers

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ByThe Brew Mechanic
We show how an alcohol hydrometer for distilling works

Understanding alcohol content is crucial, and this is where the distilling alcohol hydrometer and fermentation ABV hydrometer come into play. These tools, essential for brewers, measure the alcohol by volume (ABV) in a wash after fermentation and before distillation, providing vital information about the initial and final gravity of the wash. Additionally, a refractometer offers an alternative means to assess sugar content through light refraction, presenting a simpler option for first-time brewers.

The Role of a Distilling Alcohol Hydrometer for a Brew

A distilling hydrometer (proofing hydrometer) is used to measure the per cent alcohol ABV present and purity during distillation.

This helps the distiller to make judgements when making cuts, what is happening in the still by watching the alcohol hydrometer ABV and temperature go up and down as they are linked.

Temperature Ranges for Stripping the Wash

Acetone – Foreshots56.6°C or 133.8°F
Methanol – Foreshots   64°C or 147.2°F  
Ethyl Acetate – Heads77.1°C or 170.8°F
Ethanol Range – Hearts 78.3 > 81.5°C or 172.9 > 178.7°F
2 Proponal – Tails82°C or 179.6°F
1 Proponal – Tails97°C or 206.6°F
Fuesel oils – Tails 94 > 95°C or 201.2 > 203°F

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A good brewer can easily separate the unwanted volatiles from the spirits by using the BP and temperature ranges as above. 

What is a Fermentation ABV Hydrometer and its uses?

This fermentation hydrometer measures the ABV of the alcohol present in a wash after fermentation is completed before distillation.

Mathematically OG – FG X factor = Potential alcohol from batch based on the gravities.

Tells you what alcohol % to expect after distilling the batch by checking the back of the hydrometer.

Tells you what the initial density (OG) of the wash is.  

Tells you what the final gravity reading (FG) of the wash is after fermentation is complete.

This can also help the brewer when fault finding. Like a stuck fermentation. 

What is a Refractometer used for?

This instrument does not measure density like a glass type of hydrometer but measures the sugar content through the refraction of light through the sample. For first-time brewers, the glass hydrometer is cheaper and simpler to use but there are rules to follow. 

How does the hydrometer work?

Hydrometers are in two classes. Those that measure the density of liquids heavier than water and those that measure the density of liquids lighter than water.

Each hydrometer is unique as it has been calibrated to only measure the density of the product. Consists of a glass tube with measurements on the side and a bulb that has been weighted and calibrated to measure the density of the product. 

How to use the Alcohol hydrometer

Take a sample of the solution to be checked, and pour into a test tube.

Insert a calibrated alcohol hydrometer into the solution, it will only measure the percentage alcohol and purity. Based on the results the brewer will make changes to the still to match the ABV required?

DIY Brewers should have an inline alcohol meter in the parrot to constantly measuring the ABV all the time. 

How do you tell if the fermentation is complete without using a hydrometer?

Monitor the rate of air bubbles from the airlock, when this stops it is linked to the end of the fermentation cycle.

Press the lid gently to check for bubbles escaping. No bubbles fermentation completed.

The top section of the wash becomes lighter which indicates that fermentation is complete.

Taste the sample should be slightly bitter no sweetness is also a way to check.

You will notice globules starting to drop down indicating fermentation is complete

Maintenance and Care of Fermentation / Distilling Hydrometers

Short and simple. The hydrometers are made from glass and are round. Put them down on a flat surface they will roll and break. Make a soft sock that they can be pushed snugly into for protection. Touch wood I have never had one break as I treat them with respect.

Common Mistakes to Avoid When Using a Hydrometers

Cracked or small cracks in the hydrometer dump as it will give inaccurate readings.

After each test wipe them clean with ethanol then store them inside a soft snug sock to protect them.

Hydrometers are temperature dependant. Calibration is done at 20 Celsius or as prescribed on the item. If the sample checked is higher or lower than the pre-set one the measurement will vary.

Before checking the reading swirl the top section around like a top? This is to make sure no bubbles are in the solution being tested.

Take the reading when the hydrometer in the centre of the test tube, make sure it does not touch the sides of the test tube. Read the meniscus.

How to check and see if the hydrometer is correct? Fill up the test tube with distilled water, insert the hydrometer should read one, then you are good to go.

You can test your alcohol hydrometer against a known alcohol percentage sample kept for this test as above.

Choosing the Right Distilling Hydrometer for Home Use 

When buying a hydrometer you must look at cost and ease of using it. The simplest and cheapest ones are the glass type. I would suggest a simple glass hydrometer, once you are at the next level look at a refractor meter for as it many plusses. Here there are two refractometers one for alcohol and one for fermentation.

Types of Hydrometers for measuring alcohol content 

There are many types of alcohol meters to buy. At the end it is your call based on your budget, what you want is something simple.

Choosing this product which is an alcohol hydrometer ABV reader.

 Alcohol hydrometer Glass tube (Best one to use)

Alcohol hydrometer that only checks for percentage ABV alcohol in water solution.

Learn More

Fermentation
Hydrometer

Fermentation hydrometer to test for specific gravity. OG & FG 

Learn More

Taking samples for Hydrometer testing and preventing contamination

One of the big challenges when taking samples is not to contaminate the batch as you must open the lid to do this.

Before opening the lid make sure that equipment used to remove the sample is well sanitised.

Remember the first phase is aerobic (oxygen).

Second phase when taking samples must be fast and prevent oxygen from getting into the reaction which is anaerobic (no oxygen). When opening the lid you should see small bubbles on the surface, CO2 escaping which will prevent oxygen from entering.

You should not put that taken sample back into the batch to prevent contamination.

Last Updated on Nov 20, 2023 by The Brew Mechanic

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With 35 years of knowledge of being a chemical engineer in alcohol manufacturing plants, my mission is to teach the next generation of home distilling alcohol brewers at a supernatural speed.

My reviews are based on real-life experiences with reflux stills, sugar wash, troubleshooting and mystical chemical reactions.

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