We receive many calls and emails here at Mr. Beer on how to use a hydrometer. Many of the hydrometer instructions can be confusing to newbies so we thought we would create this primer on the correct way to use a hydrometer and the explanation of specific gravity.
Understanding Your Hydrometer:
The hydrometer is a simple instrument that measures the weight (or gravity) of a liquid in relation to the weight of water.
Because the relation of the gravity to water is specified (1.000), the resulting measure is called a specific gravity. A hydrometer will float higher in a heavy liquid, such as one with a quantity of sugar dissolved in it, and lower in a light liquid, such as water or alcohol. The average homebrewer has a very keen interest in the amount of sugar dissolved in their wort, because yeast converts sugar into carbon dioxide and alcohol. By knowing how much sugar one started with and ended with, one can easily calculate the resulting alcohol content.
There are many variants of the hydrometer. Some have only one scale, some two, and some three. The typical hydrometer measures three things: specific gravity (S.G.), potential alcohol (P.A.), and sugar.
How To Use Your Hydrometer:
It’s really pretty easy to use the hydrometer; just follow these simple steps:
- Sanitize the hydrometer, test jar, and any tools that may come into contact with your wort/beer.
- Place test cylinder on flat surface.
- Draw a sample of “clean” wort/beer. (Avoid testing samples that contain solid particles, since this will affect the readings.)
- Fill the test jar with enough liquid to just float the hydrometer – about 80% full.
- Gently lower the hydrometer into the test jar; spin the hydrometer as you release it, so no bubbles stick to the bottom of the hydrometer (this can also affect readings).
- Making sure the hydrometer isn’t touching the sides of the test jar and is floating freely, take a reading across the bottom of the meniscus (see image below). Meniscus is a fancy word for the curved surface of the liquid.
- Be sure to take good records of your readings!
That’s it! Pretty simple, huh?
There are a couple of other things you need to know to get an accurate measurement:
Most hydrometers are calibrated to give correct readings at 59-60 degrees Fahrenheit. Higher temperatures thin the liquid slightly and result in lower readings than you’d get at the correct temperature. At 70 degrees F., the reading will be 0.001 low. To correct it, add 0.001 to the reading. At 77 degrees F., add 0.002. At 84 degrees F., add 0.003. At 95 degrees F., add 0.005. At temperatures above 95 degrees F., you risk killing your yeast and losing your beer. If you can’t remember all that just print out the chart below.
Another thing you need to know is that most hydrometers come with three scales. Specific Gravity, Balling, and Brix are the ones that are usually on your hydrometer. Specific Gravity and Brix are the ones that are most used. Sugar can be measured as ounces per gallon, or as degrees Balling, or Brix. Ounces per gallon are measured on a numeric scale in which an S.G. of 1.046 equals 16 oz. (one pound) of sugar per U.S. gallon. Brix is measured as a percentage of sugar by which pure water has a Brix of 0 (or 0% sugar), an S.G. of 1.046 equals a Brix of 11.5 (11.5% sugar), and an S.G. of 1.095 equals a Brix of 22.5 (22.5% sugar). If you have a choice and want to simplify your life, buy a hydrometer that measures sugar by ounces per gallon.
That should cover everything you need to know about your hydrometer and how to use it. Here are a couple tools that may also help: