Throughout the brewing process, it is important to keep detailed records in your Brew Log of the Specific Gravity.
As a refresher, Specific Gravity is the density of your liquid. It is important to track the density of your liquid because this information is used to ultimately log the ABV (alcohol by volume) of your finished beer, and will also tell you when your beer is done fermenting.
Benjamin Stange has a solid summary of what Specific Gravity is, but in a nutshell Specific Gravity is the measurement of a liquid’s density compared to that of water. Water has a Specific Gravity reading of 1.000 (at 60°F), so anything above means the density of that liquid is higher than water.
When it comes to brewing beer, the liquid will be denser than water because we’ve added ingredients to it (sugars, starches, etc.). Over time, the measurements for Specific Gravity will fall, because the yeast we’ve added has consumed the sugar and transformed that into alcohol (which isn’t as dense as water).
Probably the most common way for a home brewer to measure the Specific Gravity of their brew is using a hydrometer. A hydrometer looks a bit like a thermometer, and works to provide a Specific Gravity reading by displacing the liquid it is floating in. Hydrometers are inexpensive, but they require additional calculations to get an accurate reading, and also require using up beer to test (never return that tested, unfermented beer back to your fermenter as you risk contamination!).
For those looking to advance beyond beginner home brewers, we recommend adding an alternative tool to your repertoire: the refractometer. When making this recommendation, we’re often asked two things: what is a refractometer, and why should I use a refractometer instead of a hydrometer?
- What is a refractometer?
A refractometer is traditionally a laboratory device used to measure refraction (how light propagates itself through a tested material). By virtue of my father being a doctor, we had access to a refractometer, and we’ve since learned that this device is used by more serious brewers.
The more sugar in a liquid, the more light will bend when going through it. Knowing this information, it is possible for a home brewer to identify how much sugar is in their wort/beer.
- Why should I use a refractometer instead of a hydrometer?
There are several benefits to using a refractometer over a hydrometer, including wasting less liquid (only a few drops vs. a graduated cylinder full), needing less equipment for testing (no need to use a graduated cylinder or thermometer), waiting less for the tested liquid to cool, and exposing less of the beer to possible contamination (only a small, sanitized pipette needs to be introduced to your fermenter).
Conversely, there are several downsides that come from using refractometer, including the additional cost (expect to spend a minimum of $30), potential difficulty reading the instrument, and the need to run calculations to convert Brix measurements (the reading taken on refractometers) into Specific Gravity. Luckily for those who are math adverse, there are free online conversion calculators that will make this calculation for you.
At the end of the day, both the hydrometer and the refractometer have their place. But for those looking for added convenience and increased accuracy, we suggest exploring investment in a refractometer.
We’d love to hear from others out there! Do you have experience using a refractometer? Any tips or suggestions on how to get the most out of the tool? As always, we invite you to join the conversation and share your thoughts below.
