guide to hydrometers

Brewing your own beer is a rewarding and challenging task — one brew may produce the crisp and refreshing IPA of your dreams, and the next beer may be a total flop. The brewing and fermenting process has many variables that impact the success or failure of a brew, but monitoring these variables can help you to improve your beer with each batch.

If you want to produce high-quality and consistent results from each brew, it is essential to test the specific gravity of your beer during fermentation. Using a hydrometer is a simple way to monitor the fermentation of your beer that has a big impact on your final product. Read on to learn more about this essential tool in every brewer’s belt and how it can help you produce the best beer ever.

What Are Hydrometers?

Hydrometers are instruments that measure the density and specific gravity of a liquid. Specific gravity is how dense a liquid is compared to water and is calculated by dividing the density of a liquid by the density of water.

what are hydrometers

Hydrometers are typically made of a long glass cylinder with a weighted bulb at one end that allows them to float upright in the liquid they are measuring. Traditional hydrometers have a scale printed on the side that shows the specific gravity as the value at the surface of the liquid. Newer technology has produced digital hydrometers that do not require a manual reading but instead display specific gravity and density electronically.

How Do Hydrometers work?

Hydrometers use displacement to calculate the density and specific gravity of a liquid. When the hydrometer is placed in a liquid sample, it displaces some of the liquid. The volume of liquid that is displaced is then used to measure its density.

Hydrometers are calibrated to measure density and specific gravity at a certain temperature because liquids change density when they change temperature. The specific gravity measurement of a hydrometer is based on the density of water at a particular temperature, so to receive accurate results, the liquid you are testing must be the temperature specified on the hydrometer. If you’re unable to measure the test liquid at the correct temperature, be sure to adjust the specific gravity reading on the hydrometer.

How to Use a Hydrometer

Using a traditional hydrometer requires taking a sample of the liquid you want to test and placing it in a test jar. This jar should be large enough that the hydrometer does not touch the edges of the container and can float freely. Below are the steps for using a standard hydrometer:

  1. Place the hydrometer into the sample you are testing with the bulb end down.
  2. Twirl the hydrometer to remove any air bubbles.
  3. Allow the hydrometer to settle until it is stabilized in a vertical position and not in contact with the test jar.
  4. Take the hydrometer reading by getting eye level with the surface of the liquid.
  5. Record the specific gravity at the bottom of the meniscus of the test liquid in the hydrometer.

Common Uses for Hydrometers

Hydrometers are most commonly used in wine-making and beer brewing, but they have applications in other industries as well. Here are a few ways to use a hydrometer:

  • Measuring sugar content: Solutes, such as sugar, increase the density of a liquid. Hydrometers can measure this density to determine the sugar content of a beer or wine. Measuring the original sugar content of a wort or grape juice prior to fermentation is particularly important as it is an indicator of how much alcohol the finished product is likely to contain.
  • Measuring alcohol content: Alcohol content in a beer or wine can be determined by measuring the original density and final density of the product. As sugar in the wort or juice converts to alcohol during fermentation, the specific gravity of the liquid decreases. The change in density can then be used to calculate the alcohol content, which will be described in more detail in the next section.
  • Measuring soil density: A special type of hydrometer can be used to measure the density of very small soil grains as they fall through a solution. The size of soil particles is often an important component of soil analysis.
  • Measuring fat content in milk: Hydrometers may be used to measure the density of milk. When paired with other tests, the specific gravity of milk can help determine the fat content and purity of the milk product.

uses of hydrometers

How to Use a Hydrometer for Brewing Beer

When brewing beer, hydrometers provide the crucial service of helping you determine the alcohol content of your product. They can also be used to verify the fermentation process is complete. In this section, we will dive into more detail about the uses of a hydrometer for brewing beer:

  • Determining the potential alcohol: The potential alcohol content is a prediction of how much alcohol your beer can contain when the fermentation is complete. This reading is based on how much sugar is in the initial wort. Many hydrometers include a scale for potential alcohol, and this reading can be taken prior to beginning fermentation.
  • Taking the original gravity reading: The alcohol content of your beer is determined by how much sugar the initial wort contains and how much of this is converted to alcohol during fermentation. The initial specific gravity of your wort will be influenced by the sugar content as well as other oils, starches, minerals and hop materials. Even when following a recipe, the original gravity of your wort may differ slightly from what the recipe predicts. For this reason, it is important to use a hydrometer to take an original gravity reading of your wort just before beginning fermentation.
  • Determining when fermentation is complete: As your beer ferments, it will drop in density as the sugars convert to carbon dioxide and ethanol. The fermentation process is complete when the specific gravity stops declining. While recipes and software can produce a good estimate of how long this will take, hydrometers allow you to verify that the specific gravity has stabilized. When you believe fermentation is complete, take a specific density reading with your hydrometer. Take another reading two days later to check if the specific gravity has changed. If it has remained the same, then fermentation is complete, and you are ready to start bottling.
  • Taking the final gravity reading: After you have determined that fermentation is complete, record a final specific gravity reading with your hydrometer. The final gravity should be lower than the original gravity of the wort. This final reading can also be used to determine how much sugar and unfermentable starches still remain in the beer.
  • Calculating alcohol content: Once you have recorded the final gravity, you can calculate the alcohol by volume (ABV) of your beer. First, find the change in specific gravity by subtracting the final gravity (FG) from the original gravity (OG). Multiply the change in gravity by 132.715 to get the alcohol by volume (ABV) of the beer. Set up as a formula, the calculation for alcohol content is ABV = (OG – FG) x 132.715. If you choose to take hydrometer readings while your beer is fermenting but before it is finished, you can use the same formula by replacing the final specific gravity with the specific gravity at the time you take the reading.

Tips for Using a Hydrometer

Using a standard hydrometer is fairly straightforward, but there are many factors that can influence the accuracy of your results. Here are a few ways to make sure you are taking the most accurate specific gravity reading for your brew:

  • Test the hydrometer first: Even if your hydrometer is new, you should test it to make sure it is working properly before testing a sample of wort. To test your hydrometer, fill a testing jar with distilled water that is the correct test temperature for your hydrometer. If your hydrometer is correctly calibrated, it should read 1.000 on the specific gravity scale.
  • Use the correct test temperature: When you test a sample of wort or beer, make sure your sample is at the right test temperature for your hydrometer. If the temperature of your sample is higher or lower, be sure to do a temperature adjustment of your specific density to compensate for the change in density due to temperature.
  • Maintain environmental temperature: The temperature of the hydrometer itself and the surrounding environment can also impact the accuracy of the specific gravity reading. For the best results, your hydrometer, test sample and surrounding atmosphere should be the same temperature. This is also why most hydrometers are calibrated for readings at room temperature.
  • Keep it clean: Before testing your beer, make sure the sample jar and hydrometer are completely clean. Dirt inside of the hydrometer will prevent the sample from rising evenly to get an accurate reading.
  • Give it space: Make sure the hydrometer has room to float in the sample jar without rubbing against the edges of the container.
  • Watch out for the meniscus: This is a science class and cooking basic, but it is worth the reminder. When reading your hydrometer, be sure you are at eye level with the surface of the water and reading horizontally across the surface of the liquid. The surface tension of the sample liquid will cause it to cling to the edges of the inside of the hydrometer creating a curved meniscus. For the most accurate results, read the bottom of the meniscus.
  • Do not over-test: One of the challenges of using a standard hydrometer is that you must remove a sample from your brew to test it. Each time you remove sample, you risk exposing the brew to air and bacteria, which can cause contamination. If using a traditional hydrometer, try to test your wort as little as possible to reduce this risk.

tips for hydrometers

Benefits of Using a Hydrometer When Brewing Beer

While some homebrewers simply follow recipes or trust software to produce a great brew, monitoring the progress of beer with a hydrometer provides more accurate information about what is actually happening inside your brew. Even if you follow a brewing recipe exactly, many factors can cause the alcohol content of your beer to vary from what is predicted by the recipe including your mash efficiency, starch conversion and evaporation rate during the boiling process. Testing the original specific gravity of your wort is the only way to know the actual potential alcohol of your beer.

Determining when your beer has finished fermenting can also be a guessing game when simply following a recipe. Tasting your beer may give an idea of how far along it is in the fermentation process, but using a hydrometer to test the specific gravity is a much more accurate way to know when your beer is ready to drink. Taking a reading of the final gravity also allows you to feel confident about the alcohol content of your beer. Knowing the actual ABV of your beer is especially essential if you plan to sell your final product.

Another benefit of using a hydrometer when brewing beer is to keep track of the specific gravity and temperature throughout the brewing process so you can recreate a homebrew you love. Nothing is more frustrating than finally creating that perfect beer, but not having enough notes to recreate it the same next time.

To summarize, here are a few reasons you should use a hydrometer when brewing beer:

  • Calculate ABV more accurately
  • Be sure that fermentation is complete
  • Recreate brews with better consistency

hydrometer benefits

Types of Hydrometers

Just like home-brewed beers, not all hydrometers are created equal. There are a variety of hydrometers available, all with different features and benefits. Depending on how serious you are about brewing beer and the factors you want to monitor during the brewing process, you can pick the right hydrometer for the task. Here are a few different types of hydrometers you will find on the market today:

  • Triple scale hydrometer: These hydrometers are the most common and least expensive. As the name suggests, triple scale hydrometers have three different scales that measure specific gravity, potential alcohol and the Brix degree. The Brix or Balling scale measures the concentration of sugar in the wort or brew. This basic hydrometer can measure a wider range of specific gravity, meaning it is suitable for most brew batches. However, this wider range also makes a triple scale hydrometer less precise than other types of hydrometers.
  • Precision hydrometer: A precision hydrometer has a smaller scale for more precise readings. However, depending on the variety of beers you brew, you may need to purchase more than one precision hydrometer since they have a smaller measurement range.
  • Thermohydrometer: This hydrometer has a thermometer built in, so you do not need to use two separate tools to get an accurate measurement. The built-in thermometer also helps to provide more consistent measurements.
  • Digital hydrometer: A newer development on the market, digital hydrometers offer many perks that traditional hydrometers cannot. Digital hydrometers can measure specific gravity, density and temperature with more precision than traditional hydrometers because they eliminate the potential for human error. Some digital hydrometers can also calculate alcohol content. Digital hydrometers have the benefit of adjusting for temperature differences automatically when measuring specific gravity, so you do not need to perform any additional calculations.

When choosing a hydrometer, consider the features you want to monitor and how precise you want your measurements to be. You should also consider the range of beers you hope to brew. Review any brewing recipes you plan to use to make sure your hydrometer will accommodate the specific gravity of those beers. When comparing hydrometers, remember that they are made of glass and will be fragile. Choose a hydrometer of good quality that is not prone to break or crack.

Brew Perfect Digital Hydrometer

If you are crazy about making beer and want to monitor your brew at every step of the process, Brew Perfect’s WiFi Digital Hydrometer is for you. Our state-of-the-art digital hydrometer takes readings of density, specific gravity, temperature and alcohol content every 20 minutes, so you always know exactly how your beer is fermenting.

brewperfect hydrometers

Unlike other digital hydrometers that still require you to take a sample of beer, the Brew Perfect WiFi Digital Hydrometer can be fitted directly to your brewing apparatus. This means you can keep an eye on your beer without the risk of contaminating the batch. View live readings for your brew displayed on easy-to-read graphs from anywhere with our mobile app or website, so you know exactly when your beer has finished fermenting.

Our digital hydrometer also allows you to save all of your brewing data, so you can continue to improve your beers or recreate a masterpiece brew time after time. Check out our Brew Perfect WiFi Digital Hydrometer to take your brewing game to the next level.