Tuesday, January 08, 2008
The hydrometer is a simple instrument that measures the weight--or gravity--of a liquid in relation to the weight of water. Because the relation of the gravity to water is specified, the resulting measure is called a specific gravity. A hydrometer will float higher in a heavy liquid, such as one with a quantity of sugar dissolved in it, and lower in a light liquid, such as water or alcohol. In truth, the average winemaker has no interest in the specific gravity of a must per se, but has a very keen interest in the amount of sugar dissolved in it, for yeast converts sugar into carbon dioxide and alcohol. By knowing how much sugar one started with and ended with, one can easily calculate the resulting alcohol.
There are many variants of the hydrometer. Some have only one scale, some two and some three. The typical hydrometer measures three things: specific gravity (S.G.), potential alcohol (P.A.), and sugar.
How To Use The Hydrometer
It's really pretty easy to use the hydrometer; just follow these simple steps:
1. Sanitize the hydrometer, wine thief, and test jar.
2. Place test cylinder on flat surface.
3. Draw a sample of "clean" must or wine with the wine thief - avoid testing samples that contain solid particles, since this will affect the readings.
4. Fill the test jar with enough liquid to just float the hydrometer - about 80% full.
5. Gently lower the hydrometer into the test jar; spin the hydrometer as you release it, so no bubbles stick to the bottom of the hydrometer (this can also affect readings).
6. Making sure the hydrometer isn't touching the sides of the test jar and is floating freely, take a reading across the bottom of the meniscus (see diagram to the left). Meniscus is a fancy word for the curved surface of the liquid.
7. Be sure to take good records of your readings!
That's it! Pretty simple, huh. There are a couple other things that we need to knew about the hydrometer, which will be covered next week.
Using Your Hydrometer - Part 2
Brix Scale Calculations