What is a hydrometer?
A hydrometer is a basic tool that is used to measure the ratio of a sample liquid’s density to the density of water. In home brewing, it is a necessary tool that will show you the degree to which the yeast is converting sugar into ethanol, ultimately helping you gauge the health and success of your beer’s fermentation.
Why do I need a hydrometer to make beer?
Homebrewing isn’t a cakewalk. There is a lot of time and effort that goes into it and there are many opportunities for things to go wrong. Perhaps the most important (and delicate) stage within beer making is fermentation. That is exactly why a hydrometer is so important, as it is the device that will tell you how the fermentation process is going. A hydrometer can be the single tool that alerts you of issues during fermentation, allowing you to make adjustments as needed.
How do I use a hydrometer?
Using a hydrometer isn't as complicated as you might think. It's a simple 4-step process:
You will need to take your first measurement after the cooldown, prior to pitching the yeast. The reading that you will get is called the original gravity, often referred to as “OG”. To obtain this reading, first use a beer thief to retrieve a sample of the wort and transfer it to a testing jar or cylinder. The testing container should have enough liquid in it to fully suspend the hydrometer. After transferring a sample to your test container, place the hydrometer in the wort and allow it to buoy. Wait until all air has escaped from the liquid or gravitated upward. From there it is recommended that your hydrometer be centered and vertically positioned so it can depict the most accurate reading.
The increments of your hydrometer represent specific gravity points. The level to which the liquid rises is where your gravity reading should occur (we’ll call this the liquid-air line). At this point, record the number on your hydrometer that is being crossed by the liquid-air line. A typical wort OG will be between 1.035 and 1.060. Your ingredient kit will list an OG so that you’ll have a reference for what your wort’s OG should be close to.
Note: To get the most accurate data, read the bottom of the meniscus - as in where the liquid is level and not pulled by tension up the sides of the container or hydrometer itself
Hydrometer readings are stated assuming a standard temperature of 15°C (59°F), so knowing the temperature of your wort is crucial for an accurate reading. If your temperature reading is different, be sure to calibrate.
Calculate the difference by using the table below. Simply add the "∆ Gravity" to your initial reading to obtain the correct specific gravity.
You’ll want to take another hydrometer reading when the fermentation process is complete or nearing its end. By the way, with an alcoholic content, it is now officially beer and no longer wort. This reading will be the final gravity, or “FG” and should be close to the listed FG, which is included in your ingredient kit instructions. To give you a good idea of what to look for, a typical beer’s FG is between 1.015 and 1.005 and should be about 1/4th or 1/5th of the beer’s OG.
A lot of beginners make the mistake of testing their brew too often. Remember that each time you test you are running the risk of exposing your beer to harmful air or bacteria, which can ruin an entire batch. We recommend only testing once before pitching and once after fermentation is believed to be complete. If additional testing is needed, perhaps due to stuck fermentation, do your best to use extreme caution.
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