The Care and Feeding of a Hydrometer

A hydrometer is one of those pieces of equipment that every beginning brewer should own and should know how to use.  Unfortunately, however, it is the one thing that often gets forgotten in those nascent days of brewing.  This wonderful little device was discovered by Hypatia of Alexandria in the golden years of discovery just before the beginning of the dark ages and has been used for hundreds of years in the brewing and wine industries

Hydrometers have three main components: The float, the neck, and the scale situated inside that is used for measurement.

Inside the neck of the hydrometer is a scale calibrated to one or more systems of measurement such as Specific Gravity (beer), Plato (beer), Brix or Balling (wine).  Some hydrometers have multiple scales such as in the picture showing a Beer/Wine hydrometer that has Specific Gravity, Potential Alcohol, and Balling scales.  Some of the more expensive models will have a thermometer in the bulb so that the temperature of the sample can be taken as well. A hydrometer works by displacement, much in the way a ship floats on water.  If we were able to change of the water by making it thinner or thicker, the ship would float higher or lower respectively. Wort or Must is a liquid saturated with sugar, the more sugars the thicker the liquid and the more it displaces the hydrometer.

When using a hydrometer there are a few things to remember:

  • Work with cooled samples: The liquid sample should be as close to the hydrometers calibration temperature (usually around 68oF) as possible.  If you are working with hot liquids, let it cool below 120o F before putting the hydrometer in the sample jar.  Rapid changes in temperature could cause the glass to crack or burst.
  • Be Accurate: Most hydrometers come with a calibration table to show you the change in specific gravity due to temperature, allowing you to sample somewhat hotter samples
  • Always work in the sample jar:  Never use your hydrometer in the boil kettle, bottling bucket or fermentor.  Contamination issues aside, the float is weighted with lead and that would not be a good additive for your hard earned beer or wine.
  • De-gas your sample: The bubbles in a partially or fully fermented sample can give you a falsely high reading.  De-gas with agitation or letting the sample sit for 20 – 30 minutes
  • Properly dispose of your sample: Unless the wort is still boiling the sample never goes back from whence it came.  This practice opens the beer or wine to infection and could potentially ruin the batch.
  • Always take the reading at the same place:  The preferred place to take a reading is at the bottom of the meniscus.  The meniscus is a “U” shaped depression caused by the liquid clinging to the side walls of the hydrometer and the sample jar.

This is simple device can increase the accuracy of your brewing or wine making, allowing you to attain the quality that you want.  Come into Kettle to Keg and see Jesse, he will help you pick the Hydrometer that’s right for you.