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The science of alcohol
The science of alcohol

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4.1.1 Using a hydrometer

In order to calculate the strength of your homebrew you will need to take two readings – one at the start of the brewing process, and one when it has completed. In Week 8 you will learn how to use these two readings to calculate the strength of your homebrewed beer.

Now watch the following video showing the use of a hydrometer to take your first homebrew reading at the start of the brewing process.

Download this video clip.Video player: soa_alcohol_boc_vid003.mp4
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A hydrometer works on the principle that water has a specific gravity of 1.000. Prior to fermentation your beer will contain sugars which make the liquid denser and so the hydrometer will float higher in the liquid than in water and will therefore give a higher specific gravity reading. For example, the starting specific gravity for an average ale or lager will be in the range 1.038–1.050. This reading is termed the original gravity, or OG.

Following the instructions in the video, you should now take a reading of your OG for your homebrew. Make a careful note of this, as you will need it in Week 8.