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Using a Hydrometer
The hydrometer is an instrument designed to measure the density of liquids. Because the density of wort or must is closely related to its sugar content, and because its sugar content is closely related to its eventual alcoholic content, the hydrometer can be used to determine the potential strength of a beer or wine.

Specific Gravity
Specific gravity is defined as density relative to the density of water. To test, insert the hydrometer into a test jar full of water (The tube the hydrometer comes in can be used as a test jar). The stem of the hydrometer will protrude above the surface of the water right at the mark that shows a Specific Gravity of 1.000.

The original gravity is the amount of fermentable sugar present. This reading is taken before the yeast is pitched and fermentation begins. Original gravities vary widely. Generally, the higher the original gravity, the stronger the final product.

ORIGINAL GRAVITIES FOR BEER: Stronger Beers 1.123 <-------> 1.030 Weaker Beers

During fermentation the gravity steadily drops as sugar is converted into alcohol and carbon dioxide. After one week of fermentation, you should take a hydrometer reading daily until you get two consecutive, identical readings. With primary fermentation completed your beer or wine has reached its final gravity and you are ready to bottle or move it into your secondary fermenter. Final gravity is the measurement at the end of fermentation, when the yeast has consumed all of the sugar it can. Again the final gravities vary depending on the style of beer or wine you are making.

FINAL GRAVITIES FOR BEER: Sweeter Beers 1.020 <-------> 1.005 Drier Beers

A hydrometer can also be used to estimate the alcohol content. To do this, take a reading before the fermentation begins, and another after it ends. For this reading, you should use the ?potential alcohol? scale. Subtract the original reading from the final reading.

The easiest way to get a sample for testing is to use a thief. Immerse the sanitized thief into the beer or wine, and put your thumb over the hole at the very top of the thief. Withdraw the thief, and position it over your sample jar. Lift your thumb, and the thief will empty itself into the jar. Repeat until you have collected an adequate sample.

Accurate measurements

  • Hydrometers are only accurate at a specific temperature, usually 60º F. Unless the sample is very hot or very cold, you will only need to adjust the reading by 1 or 2 points.
  • When taking a hydrometer reading, make sure the hydrometer is not touching the side of the sample jar. The contact with the jar can cause the hydrometer to get ?stuck?, causing an inaccurate reading.
  • Gas bubbles can cling to a hydrometer can distort the reading. Spin the hydrometer to dislodge the bubbles, and take a reading before they form on the hydrometer again. Or, you can de-carbonate the beer by pouring it back and forth between two glasses.