Hydrometer Confusion
November, 2015 Filed in: Wine making
One of the most common difficulties with winemakers is the hydrometer. It can be somewhat daunting for newbies, so we thought we would focus this month on hydrometers. First off, we know that “hydro” means water, so in fact that fragile glass device is a water meter, but not to be confused with the meter for those monthly water bills that tell us to shorten our shower times.
No rather, this water meter, measures the density of liquids, but more so it measures the relative density of a liquid. What does that mean? Well the hydrometer is calibrated so that the density of pure water is 1.00. We will leave it to the geeks to tell us that this changes with temperature, but for simplicity the specific gravity of pure water is 1.00. Therefore a good way to measure the accuracy of your hydrometer is to put it in water and make sure that the water floats to the 1.00 line.
Quite obviously the density of wine juice is higher than water, it is thicker. The typical density or specific gravity of the must (the term we give to wine before we add or pitch the yeast) is generally between 1.080 and 1.090. This essentially means your wine is 8-9% more dense than water.
Now alcohol is less dense that water, in fact the specific gravity of alcohol is approximately 0.8, or 20% less dense. So, as the yeast consumes the sugar in the wine, and converts it to alcohol, you are lowering the gravity of the must. After fermentation is complete, the specific gravity of you wine should be at, or slightly less than 1.00, usually 0.996. And you thought you would never use your high school science classes!
Of course you can use your hydrometer to determine the final alcohol of your wine. Simply record the starting specific gravity, remember to stir your wine well to get a true reading. And then record the final specific gravity. Subtract the initial specific gravity from the final, and multiply that result by 131, which is a conversion factor. That resulting number is the alcohol content of your wine in percentage terms. For an approximate number, you can use the other scale on your hydrometer, but again you have to record the initial and the final number. Fail that, come into the store and we will give you a lesson on how to use your hydrometer. That’s why we are here!
No rather, this water meter, measures the density of liquids, but more so it measures the relative density of a liquid. What does that mean? Well the hydrometer is calibrated so that the density of pure water is 1.00. We will leave it to the geeks to tell us that this changes with temperature, but for simplicity the specific gravity of pure water is 1.00. Therefore a good way to measure the accuracy of your hydrometer is to put it in water and make sure that the water floats to the 1.00 line.
Quite obviously the density of wine juice is higher than water, it is thicker. The typical density or specific gravity of the must (the term we give to wine before we add or pitch the yeast) is generally between 1.080 and 1.090. This essentially means your wine is 8-9% more dense than water.
Now alcohol is less dense that water, in fact the specific gravity of alcohol is approximately 0.8, or 20% less dense. So, as the yeast consumes the sugar in the wine, and converts it to alcohol, you are lowering the gravity of the must. After fermentation is complete, the specific gravity of you wine should be at, or slightly less than 1.00, usually 0.996. And you thought you would never use your high school science classes!
Of course you can use your hydrometer to determine the final alcohol of your wine. Simply record the starting specific gravity, remember to stir your wine well to get a true reading. And then record the final specific gravity. Subtract the initial specific gravity from the final, and multiply that result by 131, which is a conversion factor. That resulting number is the alcohol content of your wine in percentage terms. For an approximate number, you can use the other scale on your hydrometer, but again you have to record the initial and the final number. Fail that, come into the store and we will give you a lesson on how to use your hydrometer. That’s why we are here!