It is important to know that brewing is not an exact science. The yeast is a living organism, and may behave in a different way than expected. It is therefore important that you do not rely on only one parameter to decide when to bottle.
Your beer is ready to be bottled:
- when there is no more activity in the airlock;
- and when your final gravity (use a hydrometer to determine the specific gravity) is more or less equal to the expected SG;
- and if your SG has remained stable for 48 hours.