Alcoholmeter vs Hydrometer: Which One Do You Need?

Australian legal note: In Australia, using a still of any size to distil alcohol requires an excise manufacturer licence, and the ATO does not grant licences to distil spirits for personal consumption. Stills over 5 litres also need ATO permission to own. Brewing beer, cider and wine at home for non-commercial use needs no licence. This guide covers measuring commercially bought spirits, liqueur bases, home ferments and licensed operations. See the ATO's guidance on stills for the current rules.

If you pop into our Laverton North or Epping store for "a hydrometer", it helps to know what you are measuring first. It sounds fussy, but it matters. A sugar hydrometer and an alcoholmeter look almost identical, two slim glass floats with a weighted bulb and a paper scale, yet they are built for completely different liquids. Use the wrong one and the reading is not just a bit off, it is meaningless.

This guide explains what each instrument measures, why an alcoholmeter cannot read a fermenting wash, and which one belongs in your kit.

How a hydrometer works

Every hydrometer works on the same principle. It floats, and how high it floats depends on the density of the liquid around it. In a dense liquid it rides high. In a light liquid it sinks lower. The scale on the stem converts that float height into a number you can use.

Two things change the density of the liquids we work with:

• Sugar makes a liquid heavier. Grape juice, wort and a fresh sugar wash are all denser than water.
• Alcohol makes a liquid lighter. Ethanol is noticeably less dense than water, so the more alcohol in a mixture, the lower a hydrometer sinks.

The difference between the two instruments is simply which of those effects the scale has been calibrated to read.

The sugar hydrometer: for washes, wort and must

A brewing or winemaking hydrometer reads specific gravity (SG), the density of your liquid compared with water. Pure water reads 1.000. Sugary liquids read higher. Our Wine and Beer Hydrometer, for example, covers SG 0.980 to 1.160 on a 33cm stem, which spans everything from a heavy fruit must down to a fully fermented dry wash.

A sugar hydrometer does not measure alcohol directly. Instead you take two readings:

• Original gravity (OG) before the yeast goes in.
• Final gravity (FG) once fermentation has finished and the reading is stable for two or three days.

As yeast eats sugar and makes alcohol, the gravity falls. The size of that drop tells you roughly how much alcohol was produced. Plug your OG and FG into our Spirits Calculators and you will get an estimated ABV for the wash.

If you are new to reading one, start with How to Take a Hydrometer Reading for Home Brewing, then Understanding Wash Gravity Readings for what the numbers mean in a sugar wash.

The alcoholmeter: for spirit only

An alcoholmeter (also written alcoholometer, or alcoolometro in Italian) is a hydrometer whose scale reads straight in percent alcohol by volume, usually 0 to 100%. It is calibrated on the assumption that the liquid contains only alcohol and water, at a set reference temperature.

That single assumption is the whole story. Put an alcoholmeter into anything that contains sugar, fruit solids, glycerine or flavouring, and those extra ingredients add weight. The instrument floats higher than it should and shows less alcohol than is really there, often far below the true strength in a wash.

We stock a few Italian-made options:

• Italian Alcoolometro Tralles 0 to 100%
• Italian Gay Lussac Alcoholmeter 0 to 100%
• Grappa Alcohol Hydrometer 30 to 60%, a narrow-range instrument
• Alcohol Hydrometer 0 to 100% Eco range, 300mm

Tralles and Gay-Lussac are the names of the scales, after the scientists who developed them. Both read alcohol by volume. A narrow-range meter like the 30 to 60% grappa hydrometer only has to cover 30 percentage points on its scale, so the graduations can be spaced further apart and are easier to read within that range. It is handy when you only need to check spirit that falls inside those limits.

Why temperature matters more with an alcoholmeter

Alcohol expands more than water as it warms. A warm sample is lighter, the alcoholmeter sinks lower, and the reading comes out higher than the true strength. A cold sample does the opposite.

Every alcoholmeter is calibrated at a specific reference temperature, which is printed on the instrument or its paper scale. For an accurate reading, bring the sample to that temperature, or use a temperature correction table. Check the temperature with a reliable thermometer such as the Mad Millie Boxed Thermometer before you read.

Side by side

• Sugar hydrometer: reads specific gravity. Use it on wort, must, juice and fermenting washes. Two readings (OG and FG) give an estimated ABV.
• Alcoholmeter: reads % ABV directly. Use it only on clear spirit that is alcohol and water. Useless in a wash, a liqueur or anything sweetened.
• Refractometer: reads sugar (Brix) from a few drops of unfermented juice or wort. Handy at harvest, but alcohol skews the reading once fermentation starts. See our Portable Refractometer and How to Read a Refractometer When Brewing Beer.
• Vinometer: a quick, rough indication of alcohol in dry wine only. The Italian Vinometer Cup Type 0 to 25% is a traditional cellar tool, not a precision instrument.

What about liqueurs?

This is where people get caught. Once you add sugar, syrup or a liqueur base to spirit, an alcoholmeter can no longer read it accurately. Measure the spirit strength before you sweeten it, then work out the final ABV by calculation. Our guides on Understanding Alcohol Dilution and Blending Spirits and Liqueurs walk through the maths, and the Spirits Calculators will do it for you.

How to take an accurate reading

• Use a tall, narrow trial jar so the hydrometer floats freely. Our Hydrometer Test Cylinder 270ml is one option. Check the cylinder is tall enough for your instrument to float without touching the bottom.
• Make sure the instrument and jar are clean and dry. Residue changes the reading.
• Lower the hydrometer gently, then give it a light spin to knock off any clinging bubbles.
• Read at eye level, at the flat surface of the liquid rather than the curved edge where it climbs the glass.
• Note the temperature at the same time and correct if needed.
• Write it down. A running log is gold when you look back at a batch. See Record Keeping for Distilling Runs.

A note on parrots

In licensed distilling operations, a "parrot" sits under the still's output and holds an alcoholmeter in the running spirit, so the operator can watch strength change during a run. Options include the Distillation Parrot in stainless steel and the PolyPhoenix Adjustable Distillation Parrot. Readings in a parrot are taken on warm spirit, so treat them as a guide and confirm at the reference temperature.

Caring for glass hydrometers

They are thin glass and they do break, usually by rolling off a bench. Store them in their tube, rinse with clean water after each use, and never stand one up in an empty jar. If the paper scale inside has slipped, the instrument is no longer accurate and should be replaced.

Frequently asked questions

Can I use an alcoholmeter to check my beer or wine?

No. Beer and wine contain residual sugars and other dissolved solids, so an alcoholmeter will read well below the true strength. Use a sugar hydrometer and calculate ABV from your OG and FG.

Why does my alcoholmeter read so low in a fermented wash?

Because the wash still contains sugars, yeast and nutrients that add density. The instrument is calibrated for alcohol and water only, so it cannot read a wash. That is the job of a sugar hydrometer.

Do I need both?

If you only brew beer, wine or cider, a sugar hydrometer is all you need. If you also blend liqueurs or work with finished spirit, an alcoholmeter is worth having for checking strength before sweetening.

Is a narrow-range alcoholmeter more accurate?

It can be easier to read precisely, because the graduations are usually spread further apart. It only works inside its range, so a 30 to 60% meter cannot read a 70% spirit or a 20% liqueur base.

What temperature should I read at?

The reference temperature printed on the instrument. If your sample is warmer or cooler, either bring it to temperature or apply a correction.