Using a Hydrometer
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.
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