Hydrometers

Hydrometers measure the 'gravity' of your wort. The more sugars in the wort then the higher the gravity. As the sugar is converted to alcohol the gravity readings will lower.

This is useful to the home brewer as he/she can use the hydrometer to both check the content of alcohol in a beer and also check to see if fermentation has ceased.

The process of hydrometer readings starts with a reading from the fermenter prior to fermentation. This reading is known as the Original Gravity (OG). Through this reading the brewer can check if the gravity is that indicated by the recipe and add sugar if required to raise the gravity.

Once the airlock has ceased bubbling the brewer should then check the gravity of the brew. This is known as the Final Gravity (FG). If the FG is too high then the brewer may gently stir the wort to reactivate any yeast and continue fermentation and leave for 24 hours or until there is no bubbling from the airlock.

To ensure that the fermentation process has ended it is worth taking a couple of readings over a 24 hour period. If the FG remains the same then it is time to bottle or barrel the brew.

It is possible to take a hydrometer reading directly from your fermenter however it is easier to take a reading using a sanitised test jar filled with a sample of the wort.

Hydrometers are calibrated to be accurate at a certain temperature ie. 20°C. It is vital that you take a temperature reading when taking both the OG and FG readings. There are many correction charts available on the internet but you will need to find one that matches the calibration of your hydrometer.

Don't forget your hydrometer and thermometer must be clean and sanitised.

Calculating the Alcohol Content. ABV.

There are many methods for finding out the Alcohol By Volume (ABV) of your beer - some more accurate than others.

I use a simple equation to work out the ABV although if you do searches on the internet you will find many other more complex equations to determine alcohol content. I am only concerned about the ABV to the nearest 10th and the equation I use seems to be adequate and simple.

ABV% = (Original Gravity - Final Gravity) ÷ 0.79

Example: A beer with an Original Gravity of 1.045 and a Final Gravity of 1.008 will have an ABV of 4.9%.