A hydrometer is a measuring tool, usually made from a weighted glass tube, used to test the density of a liquid. The idea behind the hydrometer is that suspending a solid object in a liquid will cause the former to float to the same degree as the weight of the displaced fluid. This means that the tool will sink lower into a less dense liquid. Brewers use hydrometers to track the progress of beer or other fermented beverages, as the density of the liquid decreases as the yeast converts the sugar to alcohol.
Steps
Part 1 of 2: Take a Reading
Step 1. Check the gauge's temperature calibration
Density meters measure the density of a liquid, but liquids expand and contract with changes in temperature. To get an accurate response, you need to test the liquids at the temperature for which the gauge was designed. This temperature should be indicated on the hydrometer label or in the instructions on the same package.
- Most home density meters are calibrated at 15 or 16 ° C (59 or 60 ° F), and most laboratory density meters are calibrated at 20 ° C (68 ° F).
- Hydrometers can lose accuracy over time. If you are using an older tool, you may want to try it first.
Step 2. Measure the temperature of the liquid
If it is more than a degree or two below the gauge's intended temperature, record the result. The measurement will be wrong, but you can correct it using the temperature table at the end of this article.
If you're testing homemade beer wort, don't contaminate it with an unsterilized thermometer. Use a tape thermometer that you stick to the side of the container, or measure a sample instead of the main batch
Step 3. Pour a sample into a clean container
Choose a clear jar or cup large enough so that the hydrometer can float without hitting the sides or bottom of the container. Transfer a sample of the liquid to this container.
- When brewing, taste the wort after the visible signs of fermentation have finished, but before adding the yeast. Transfer the sample using a siphon, wine pipette, or suction bulb. Each object must be sterilized.
- If accuracy is extremely important, rinse the container with a small amount of the liquid before adding the entire sample.
Step 4. Insert the hydrometer into the liquid
Make sure the hydrometer is dry, and then dip it into the liquid, just below the point where it would naturally float. Make sure the gauge bulb does not touch the sides or bottom of the jar when it sets.
Step 5. Turn the gauge gently
This will dislodge air bubbles clinging to the tool, which were disrupting the measurement. Wait for the hydrometer and liquid to stop moving and for the bubbles to dissipate.
Step 6. Read the scale of the hydrometer at the lowest point on the surface of the liquid
The surface of the liquid can adhere to the hydrometer and to the walls of the container, forming a curve called the meniscus. Look for the scale mark on the gauge level, next to the "lowest" point on the surface of the liquid. Do not use the mark where the fluid touches the gauge.
Step 7. Understand the measurement
The most common scale on hydrometers is "specific gravity." It is the relationship between the density of the liquid and the density of water. Pure water should give a reading of 1,000. A higher reading means the liquid is denser (heavier) than water, and a lower reading means it is lighter.
The specific gravity of the wort (called original gravity or GO by brewers) varies greatly. The more sugar in the wort, the higher the GO, and the higher the alcohol content in the final result. Most beer GOs are in the 1.030 to 1.070 range, but can be significantly higher
Step 8. Interpret the Plato, Balling, or Brix scales
The gauge may use one of these scales instead, or you may need to convert the measurement to follow a certain recipe. Here's how to measure density using these three units:
- The Plato scale measures the percentage of sucrose in a wort, so 10º on the Plato scale means that 10% of the wort is sucrose by weight. Multiply the Plato measurement by 0.004 and add 1 for an estimate of specific gravity, which is close enough for a homebrew. For example, a wort rated 10 on the Plato scale has a specific gravity of 10 x 0.004 + 1 = 1.040. The further you go from this number, the less accurate the conversion.
- The Balling and Brix scales measure the concentration of sugar in a solution, but the units are close enough to the Plato scale that they can be used interchangeably for home brewing. Commercial breweries use more accurate conversion formulas, and perform their own tests to calibrate the Brix scale based on various factors.
Step 9. Take a reading of the last sample
At the end of the entire brewing process, test additional samples daily with the hydrometer. If the reading is the same two days in a row, there are no more sugars turning into alcohol, which means the fermentation is over. The final reading at this point is the "final gravity" or "GF". The GF that should be achieved depends on the type of beer you are making, and, in some cases, the additional ingredients that affect the hydrometer reading.
- With a few exceptions, most beers have a GF of around 1.007 to 1.015.
- Homebrewers rarely get the exact GF predicted by the recipe, especially on the first few tries. It's more important that the beer tastes good, but keep your records and keep studying the process for a more consistent result.
Step 10. Estimate the alcohol by volume
The difference between original gravity and final gravity tells you how much sugar was turned into alcohol. The formula 132.715 x (GO - GF) is a useful way to convert this to alcohol by volume (ABV). Keep in mind that this is only an estimate, and is most accurate for beers with a final gravity of around 1,010.
For example, if the GO was 1.041 and the GF is 1.011, the ABV is approximately 132.715 x (1.041 - 1.011) = 3.98%
Part 2 of 2: Putting the Gauge to the Test
Step 1. Fill a container with water
To check if the gauge is accurate, use distilled water or reverse osmosis water. If you use tap water or untreated bottled water in your brewing, you can try those types of water instead. The mineral content will alter the results, but this will tell you how to adjust the readings for concoctions made with the same water.
Step 2. Bring the water to the correct temperature
The gauge's calibrated temperature should be marked on the gauge's label or in the packaging instructions.
Step 3. Measure the density of the water
Place the hydrometer in the water, swirl gently to shake off any air bubbles, and wait for it to settle. The hydrometer will read 1,000 in pure water, if perfectly calibrated.
- A hydrometer using the Plato or Balling scale will read 0.00º.
- See the instructions above for a more detailed guide on how to use the hydrometer.
Step 4. Record the correction if the gauge is inaccurate
If you get a result other than 1,000, the gauge is out of balance (or the water contains minerals). Write down the amount you need to add or subtract from future readings to correct this error.
- For example, if the hydrometer reads 0.999 in pure water, add 0.001 to all measurements.
- As another example, if the hydrometer reads 1.003 in tap water, subtract 0.003 from all measurements of liquid made from that particular tap water. Test the hydrometer again if you change your water source.
Step 5. Consider replacing or adjusting the gauge
If the gauge is very unbalanced, it is often better to order a new one. The old man may lose even more precision over time, but for a frugal brewer it is possible to correct this problem:
- If the measurement is too low, apply tape, nail polish, or any other material to increase the weight until the measurement is correct.
- If the measurement is too high, buff the edge to remove the material. Seal the rough area with nail polish to create protection against glass dust or sharp edges.
Temperature setting
-
Adjust the temperature for a standard hydrometer. If the gauge is calibrated for 16ºC (60ºF), use the following table when measuring different temperatures. Find the temperature of the liquid in column 1 or 2, and then add the number in the same row, in column 3, to the specific gravity:
(Temperature (F) Temperature (C) Adjust GE5010−0.695512.8−0.386015.60.006518.30.537021.11.057523.91.698026.72.398529.43.179032.24.01) { displaystyle { begin {pmatrix} Temperature (F) & Temperature (C) & AdjustGE \ \ 50 & 10 & -0.69 \ 55 & 12.8 & -0.38 \ 60 & 15.6 & 0.00 \ 65 & 18.3 & 0.53 \ 70 & 21.1 & 1.05 \ 75 & 23.9 & 1.69 \ 80 & 26.7 & 2.39 \ 85 & 29. 4 & 3.17 \ 90 & 32.2 & 4.01 \ end {pmatrix}}}
- Commercial brewers frequently measure density during brewing, and keep detailed records to track inconsistencies or results of different methods. That said, there is a risk of contamination every time you open the lid. In a home environment, it is usually best to check the beer as little as possible.