Before a test is made the hydrometer should be thoroughly washed, rinsed and dried by wiping with a clean, lint free cloth. The hydrometer jar should be thoroughly washed and rinsed before the clean test liquid is added.
The hydrometer and liquid should be at the temperature of the surrounding atmosphere to prevent changes in density during the testing. To ensure uniformity of density and temperature, the liquid should be completely stirred shortly before the observation is made.
Stirring is accomplished with a perforated disk or spiral on the end of a rod long enough to reach the bottom of the container. Stirring from top to bottom disperses liquid layers of different densities and aids in attaining temperature uniformity.
Readings should not be made until both liquid and hydrometer are free of air bubbles and are at rest. Temperature of the liquid should be determined by a precision thermometer and recorded along with the hydrometer reading. This will minimize any undue effect surface tension will have on the readings of the hydrometer. For all-grain brewers, having a target original gravity going into the brew day allows you to track how close certain aspects of the recipe match the actual wort. Beers, ciders and meads can have an original gravity up to and potentially over 1.
After a beer has visibly finished fermenting and it is assumed all activity is complete, a gravity reading is typically taken. The following day another reading is taken, and if they are the same it can safely be assumed fermentation is complete. Comparing the original and final gravities allows the brewer to measure the attenuation, which can help estimate the beverages alcohol content. When discussing specific gravity, brewers tend to read 1. A hydrometer is one instrument used to measure specific gravity a refractometer and sacchorometer can also be used.
Gravity readings are typically taken before pitching the yeast and after visible signs of fermentation have ceased. It is generally not recommended to take more samples than necessary because each time the fermenter is opened to draw out wort, you are introducing the risk for contamination.
To pull a sample, use a wine thief, siphon or turkey baster and take extra care with sanitation. Place the wort sample in a vessel big enough to allow the hydrometer to freely float without hitting the bottom or sides of the container.
Some homebrewers buy a test tube, or you can sometimes use your wine thief or the container the hydrometer came in. Once the liquid is in the container, place the hydrometer in the sample and give it a gentle spin. The hydrometer will eventually settle and you can take your reading. Sometimes the hydrometer will stick to the side of your vessel, so make sure it is floating freely before you take the reading. After you are finished, do not return your sample to the fermenter, as it could cause contamination.
Instead, taste the sample to get an idea of what to expect from the final product. Reading a hydrometer is as simple as noting where the surface of the liquid meets the surface hydrometer—right? It is actually a little bit more involved than that. In fact, if you take your hydrometer reading from where the liquid appears to stop, you may be taking your readings too high.
A meniscus is a curvature in liquid, and usually happens in vessels like test tubes. Carefully look where the bottom point of meniscus is and take a reading from that level.
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