HYDROMETER
WHAT: A hydrometer is an instrument that measures the density, or thickness, of a liquid compared to the density of water. This measurement is called specific gravity (SG).
WHY: The hydrometer provides two important pieces of information. One is the ability to project and calculate the amount of alcohol in your finished beer or wine. The second and perhaps more importantly, is the ability to determine when fermentation is complete. Bottling carbonated beverages before the fermentation is complete can cause the bottles to explode.
WHEN: You should take a hydrometer reading at least once before fermentation and again after fermentation. Additional readings to monitor the fermentation progress can also be helpful.
HOW: Most hydrometers have multiple scales that read specific gravity, potential alcohol (PA), and approximate sugar per liter (Sugar/L). This instruction will discuss all three scales and the purpose of each.
Remember that the hydrometer reads the specific gravity (thickness because of the sugar) of a liquid compared to water, which at 20 degrees C, has a specific gravity of 1.000. For the hydrometer to read accurately the test liquid should be at, or very near, 20 degrees. Hot liquids are less dense than cold liquids (think of cold honey versus hot honey). If you are testing a liquid that is 30 degrees C, you would need to add .003 to your specific gravity reading. Conversely, if the liquid is colder than 20 degrees you would subtract from the reading. Each hydrometer manufacturer has different correction values, so check the data sheet that came with your particular hydrometer.
Hydrometers are very fragile, so handle with care! Draw off a sample of the liquid to be tested into a test tube. (Some hydrometers come in a tube that you can use if you remove the little sponge inserts.) You can also put the hydrometer directly into the fermenter if you chose, but make sure it is fully sanitized before you do.
Gently lower the hydrometer into the liquid until it floats freely. Give it a little spin to free any bubbles that may have attached to the sides. When the hydrometer stops moving, and is not in contact with the sides or bottom, read the upper most level of the liquid on the specific gravity scale and record the reading. A reading taken before fermentation begins is called original gravity (OG).
Once you have determined the OG, rotate the hydrometer to read and record the PA. For example: A specific gravity of 1.046 has a Potential alcohol level of 6%.
Repeat the entire process after fermentation is complete to get the final gravity (FG) reading. Assuming normal fermentation temperatures, beer will ferment in 5-7 days, cider in 4-10 days, wine in 2-3 weeks, and mead could take up to several months.
To determine the finished alcohol content in your beverage, simply subtract the PA of the final gravity from the PA of the original gravity. For example:
OG of 1.060 has a potential alcohol of 7.8%
FG of 1.015 has a potential alcohol of 1.9%
Alcohol content is 5.9%
WARNING: Remember that bottling carbonated beverages before fermentation is complete can cause the bottles to explode. This is very dangerous! Healthy beer yeast will consume between 65-80% of the available sugars. You want to make sure that at least 65% of the sugar has converted before you bottle your beer (which means 35% of the sugars are left). Here is a simple equation to calculate when it is safe to bottle. If your beer has an original gravity of 1.048, subtract 1 to get .048, then multiply by 0.35, which gives you .017. You should not bottle the beer until the final gravity is below 1.017.
PUMP IT UP! You can also use your hydrometer to determine how much sugar to add to your must or wort if you want to increase the final alcohol content. For example: Let’s say you crush your grapes and find the OG to be 1.080, which if fermented to dryness will produce a wine of only 10.5%, but you desire a wine of 13.2% (OG of 1.100) . This means you will have to add sugar to the must to get the alcohol level you want. Using the Sugar/L scale you see that an OG of 1.080 equals 208g of sugar per liter. A dry wine of 13.2% (OG of 1.100) requires 262g of sugar per liter. That is a difference of 54 grams of sugar per liter that will need to be added. If you have 20 liters of must, you will need to add 1080 grams (54g x 20=1080 grams). It is best if you add half of the sugar two days after fermentation begins, then add the second half two days later. Dissolve the sugar in a small amount of warm must, add it to the fermenter, and stir gently.
Hydrometer - הידרומטר
