Most homebrew hydrometers are calibrated at 59–60°F (15–15. 6°C ), and most laboratory hydrometers are calibrated at 68°F (20. 0°C). Hydrometers can lose accuracy over time. If you’re using an old tool, you may want to test it first.
If testing homebrewed wort, do not contaminate it with a non-sanitized thermometer. Use an adhesive strip thermometer that sticks to the side of the container, or measure a sample instead of the main batch.
When brewing, test the wort after visible signs of fermentation have ended, but before pitching the yeast. Transfer the sample using a sanitized siphon, wine thief, or baster. [1] X Research source If precision is extremely important, rinse the container with a small amount of the liquid before adding the full sample.
The specific gravity of wort (called original gravity or OG by brewers) varies greatly. The more sugar in a wort, the higher the OG, and the higher alcohol content in the final beer. Most beers OGs fall in the 1. 030 to 1. 070 range, but they can be significantly higher. [3] X Research source
The Plato scale measures the percentage of sucrose in a wort, so 10 degrees on the Plato scale means 10% of the wort is sucrose by weight. Multiply the Plato measurement by 0. 004 and add 1 for a specific gravity estimate that’s close enough for homebrewing purposes. For example, a 10 degrees Plato wort has a specific gravity of 10 x . 004 + 1 = 1. 040. (The further you get from this number, the less accurate the conversion is. [4] X Research source ) The Balling and Brix scales measure the sugar concentration in a solution, but the units are close enough to the Plato scale that you can use them interchangeably for home brewing. Commercial breweries use more exact conversion formulas, and conduct their own tests to calibrate the Brix scale based on various factors. [5] X Research source
With a few exceptions, most beers have an FG around 1. 007 to 1. 015. [6] X Research source Home brewers rarely get the exact FG predicted by their recipe, especially on their first few attempts. It’s more important that the beer tastes good, but keep records and keep studying the process to get a more consistent result.
For example, if your OG was 1. 041 and your FG is 1. 011, the ABV is roughly 132. 715 x (1. 041 - 1. 011) = 3. 98%.
A hydrometer that uses the Plato or Balling scale will read 0. 00º. See the instructions above for a more detailed guide on how to use the hydrometer.
For example, if your hydrometer reads 0. 999 in pure water, add 0. 001 to all measurements. To take another example, if your hydrometer reads 1. 003 in tap water, subtract 0. 003 from all measurements of liquid brewed with that specific tap water. Test the hydrometer again if you change water sources.
If the measurement is too low, attach tape, nail polish, or any other material to increase the weight until the measurement is correct. If the measurement is too high, file the edge to remove material. Seal the rough area with nail polish to protect against glass dust or sharp edges.
