I have advanced to a very prolific brewer and have mastered many aspects of home brewing. For some reason I seem to be unable to master the issue of Specific Gravity. Try as I may, I just do not grasp it and as a result always keep my beer in fermentation longer than necessary. Any suggestions to help a slow learner?
Your question is very general, but I can point you in the right direction.
Specific gravity (SG) is the ratio of the density of a substance to the density of a reference substance. In homebrewing we measure sugars (fermentable or not) in wort.
Here are a few good articles on how to measure gravity :
Why do we need to measure it :
- To determine potential alcohol level in wort
- To determine when fermentation is finished
To determine that fermentation is completed, when aim to get a stable SG 3 days in a row (unless we suspect a stuck fermentation, which is another question).
To determine the potential alcohol, we need the original SG or OG (measured before fermentation) and the finishing SG or FG (measure at the end of fermentation). There are 2 (popular) ways to calculate it:
- ABV = 132 * (OG-FG)
- ABV = (OG-FG) / 0.00753
I would recommend that you start with an hydrometer which is not expensive and easy to use. Later if you want more options, you can buy an refreactometer wich costs at least twice as much (depending on the quality).