Starting out, homebrewing can sometimes seem an exercise in crisis management. Until you’re secure with the process, any deviation from expectations can start a cycle of worry. Since hydrometer readings are so precise, it’s easy to get hung up on those numbers. If the recipe indicates an OG of 1.057, but your measured gravity is different, how much should you care? What if your beer’s final gravity is out of line with the prediction? Is there anything you can do about it?
In general, it’s a matter of degree. If you’re within 5 points (around 10 percent or so), it’s worth some analysis, but it’s not that big of a deal. You should examine larger variations to understand what’s going on. Likely explanations and mitigation will depend on whether your issue is with the starting gravity or finishing gravity.
Eliminate the Obvious
Before you launch a full investigation, validate your measurements and your tool. Many brewers forget that hydrometer readings are temperature dependent. Each one has a reference temperature (usually 60°F/15.5°C or 68°/20°C); if your sample is significantly warmer or colder, your reading will be off. For example, wort at 100°F (38°C) will read as 1.056 on a 60°F hydrometer when it’s actually 1.062. Remember to use a temperature adjustment table or calculator if necessary. In addition, you should check that your hydrometer is correctly calibrated. It’s not unusual for the paper scale to slip slightly and skew your measurements.