Hydrometer

 

To be honest, a hydrometer is not really a requirement to have (and use) for homedistilling purposes, but.... 

Brewing and distilling is like gardening. Without an  understanding or feel for the natural processes, you'll never master the art. 

Buying a  lot of fancy equipment is not going to change that. But a hydrometer will allow us to improve our efficiency and will enable us to achieve results which are repetitive.

 

A hydrometer and the potential alcohol level

A hydrometer is an inexpensive piece of test equipment used by brewers, winemakers and distillers. It is generally made of blown glass, with a weighted, bulbous bottom and a long narrow stem  (see picture below). The hydrometer is designed to float in liquid with the bulbous end down. A reading is taken by looking at a scale (contained in the stem) where the surface of the liquid being measured. 


The Potential Alcohol (PA) level can be calculated by measuring the specific gravity (SG) of the wash, assuming all sugar will be fermented and no sugar additions are made after inoculation. PA values are calculated based on SG/Brix values, not on "Sugar" values.  This all sound technical but in fact it is very easy to do.

So, if we measure the sugar content of our wash, we can predict the final outcome of alcohol once the fermentation has stopped. 

This will allow us to:

  1. avoid wasting to much sugar on a wash which will never be fermented (yeast can only survive a certain % of alcohol before the yeast cells die.

  2. understand during the fermentation wether the fermentation stopped as a result of absence of sugar for the yeast to survive on or because of another unwanted reason.

How does it work

The easiest way to explain how a hydrometer works is with pictures. Take a look at Diagram 1, on the left, which represents a test jar full of wash before the yeast is pitched.

The hydrometer is floating rather high. This is because the liquid is "heavy" with all the sugar... the hydrometer is pushed up because of this.

As the yeast turns the sugar into alcohol and carbon dioxide, the wash becomes lighter (alcohol weighs less per unit volume) and the hydrometer doesn't float as high as it once did. Diagram 2  represents a wash that has fermented to dryness and is lighter than water.

 

Diagram 1 Diagram 2

 

How to use a hydrometer

If you want to use a hydrometer properly, you will need the following  items:

  • Trial jar

  • Thermometer

  • Wine thief (optional)

The first thing you need to do is to calibrate your hydrometer. It is a simple process which will determine wether your readings will give you any usefull information. This is what you need to do:

  • Keep a trial jar with water near your wash. The idea is that this water have the same temperature as your wash.

  • Before using your hydrometer (every time!): Check the reading of the water. It should be around 1000 s.g. (0 on some hydrometers) but it will vary depending on temperature and scale errors.

  • If your hydrometer shows, say 1002 (+2) you obviously need to take your reading minus 2 to get it right. Then simply take all your wash readings minus 2 and thats it!

  • Similarly of course, if your hydrometer shows 997 (-3) on the water - just add 3 to all your readings.

Remember that you have to check the water reading every time because temperature might have changed and/or your hydrometer scale might have moved inside the hydrometer.

  1. Sanitize the hydrometer, wine thief, and test jar. Place test cylinder on flat surface. 

  2. Draw a sample of "clean" wash with the wine thief from the wash - avoid testing samples that contain solid particles, since this will affect the readings. 

  3. Fill the test jar with enough liquid to just float the hydrometer - about 80% full.

  4. Gently lower the hydrometer into the test jar; spin the hydrometer as you release it, so no bubbles stick to the bottom of the hydrometer (this can also affect readings).

  5. Making sure the hydrometer isn't touching the sides of the test jar and is floating freely, take a reading across the bottom of the meniscus (see diagram to the right). Meniscus is a fancy word for the curved surface of the liquid. 

 

Basic rules you need keep in mind

  • If your wine contains much CO2 (i.e. still is fermenting or only just stopped) you need to be careful. The CO2 bubbles tend to stick to the hydrometer after a few seconds and then lift it up. Best trick is to give the meter a short spin, then stop it and take a reading immediately.

  • Remember to calibrate the hydrometer before you use it to get the most accurate reading.

  • Hydrometers are designed for use at a particular temperature. If the liquid is hotter (or colder) it will give a false reading. There is usually a conversion table supplied with them to help correct readings by. For a general correction table, have a look at: Correction tables

     

Some suggestions

  • The range of readings (highest to lowest), to make sure it will suit your purpose. A standard range for home brewers is 0.990 to 1.120. For example, in order to achieve a 12% wash, you'll want to start your wash at a SG of 1.090.

  • What the hydrometer measures. Some hydrometers only measure specific gravity, but most of them measure three things: SG, potential alcohol (P.A.), and sugar content. 

  • The calibration temperature of the hydrometer. The most common calibration temp is 60° F.

  • Whether sugar content is expressed in ounces per gallon (US/Imperial), or in grams of sugar per liter.

  • Whether it will fit your test jar / test cylinder.

  • If it comes with a protective case (they're pretty fragile!)

  • Don't throw back the wash sample you have used during measurement - it might ruin the batch!!!

  • Be sure to take good records of your readings! 

 

Where to get it

  • Check your local homebrew shop.  They should have hydrometers. Prices should be between the range of  $10  - $20. I would not suggest to pay much more.

  • Check the web if there is no homebrew shop in your area.