A hydrometer determines the relative density of a solution relative to the density of water. This is referred to as Specific Gravity. Sugar water will have a density that is greater than pure water. Ethanol has a density that is less than water. The hydrometer will sink further into a solution of alcohol and not sink as far into a sugar solution. Specific Gravity is unitless. It defines the ratio of the density of a solution to the density of water. Specific Gravity is calculated like so, Specific Gravity = (Density g/cm)/(1 g/cm).
Typically a hydrometer is used to determine the sugar content of something that can be fermented. This could possibly be wine must, beer or whiskey mash and even things that do not have anything to do with making alcoholic beverages. Hydrometers are scaled and calibrated for each distinct purpose. For instance, a hydrometer used to determine the sugar content and potential alcohol in a whiskey mash will usually measure the Specific Gravity in a range between ~0.990 – 1.180. If you’re measuring distilled spirits you must have a liquor hydrometer that will have a proof range from 0-200 or a tralle range from 0-100. Here is some example data that shows the Specific Gravity of some typical solutions.
Pure Water: Specific Gravity = 1.0
Pure Ethanol: Specific Gravity = 0.785
50% Ethanol: Specific Gravity = 0.8925
To measure the sugar content and potential alcohol of a mash you’ll need to use a beer and wine hydrometer. Simply take a sample of the mash and pour it into a tall graduated cylinder. The graduated cylinder might be a jar or something that is narrow and tall. Nevertheless, make sure that the cylinder is as tall or taller compared to the hydrometer. Next, lower the hydrometer into the graduated cylinder until it’s floating. Give it a little spin like a top to shake loose any air bubbles that might adhere to the hydrometer. Now you are ready to read the hydrometer. Read the number on the hydrometer that is at the same level as the liquid. You can now determine sugar content and potential alcohol presuming that both measurements are on the hydrometer.
Author: Alan SuttonThis author has published 2 articles so far.