Hydrometer - How to Use a Hydrometer


How to Use a Hydrometer

How Does a Hydrometer Work?
  • Whether you have experienced it yourself you have probably at least heard that when swimming a person floats much easier in salt water than non-salt water. What is actually happening is that salt water is heavier than non salt water so a swimmer rises to the top or floats in salt water where many swimmers do not float in non-salt water. Again, it is the salt water that is heavier than the swimmer causing the swimmer to float.
  • Similarly, wine must with sugar is heavier than wine with alcohol causing a hydrometer to float much higher in the wine must with sugar. How high the hydrometer floats in the must with sugar is dependent upon how much sugar is in the wine must. As the yeast turns the sugar into alcohol and carbon dioxide the wine becomes lighter causing the hydrometer to not float as high in the wine.
  • A Triple scalerefers to the three different measuring scales within the hydrometer. Two of the scales, the Specific Gravity scale and the Balling scale measure liquid density, while the third scale measures potential alcohol. Home Brewers seem to prefer the specific gravity scale. The first two scales measure the density of liquids relative to water. Ordinary water, at 60° F has a specific gravity of 1.000. For comparison’s sake, when measured at the same temperature, gasoline has a specific gravity around 0.66, whole milk is about 1.028, and mercury is 13.600!
  • The Balling scale performs the exact same function as the specific gravity scale, except that it reads in different incremental numbers. On the Balling scale, the gradations are called degrees Plato, OR Brix. A wine must with a Specific Gravity of 1.048 has an equivalent density of 12.5 Brix/Degrees Plato. (These two scales are relative to each other in the same sense that both Fahrenheit and Celsius scales can be used to measure air temperature).
  • Adjusting for temperature… Most hydrometers are designed and calibrated for readings to be taken of wine or juice samples at 60 degrees Fahrenheit. If your wine must is warmer than the calibrated temperature of your hydrometer add 0.25 Brix to the reading for each 9 degrees F or 5 degrees C.
Prepare to Use the Hydrometer
  • Make sure your hydrometer, hydrometer test jar and wine thief are clean.
  • Pour your juice or wine must carefully into the hydrometer jar to avoid the formation of air bubbles. Do this by pouring it slowly down the side of the jar.
Taking a Hydrometer Reading
  • Pour your juice or wine must carefully into the hydrometer jar to avoid the formation of air bubbles. Do this by pouring it slowly down the side of the jar.
  • Carefully insert the hydrometer into the juice or wine must, holding it at the top of the stem, and release it when it is approximately at its position of equilibrium.
  • Note the reading approximately, and then by pressing on the top of the stem push the hydrometer into the liquid a few millimeters and no more beyond its equilibrium position. Do not grip the stem, but allow it to rest lightly between finger and thumb. Excess liquid on the stem above the surface can affect the reading.
  • Release the hydrometer; it should rise steadily and after a few oscillations settle down to its position of equilibrium.
  • If during these oscillations the meniscus is crinkled or dragged out of shape by the motion of the hydrometer, this indicates that either the hydrometer or the surface of the liquid is not clean. Carefully clean the hydrometer stem. If the meniscus remains unchanged as the hydrometer rises and falls, then the hydrometer and liquid surface are clean, and a reading can be taken.
  • The correct scale reading is that corresponding to the plane of intersection of the horizontal liquid surface and the stem. This is not the point where the surface of the liquid actually touches the hydrometer stem. Take the reading by viewing the scale through the liquid, and adjusting your line of sight until it is in the plane of the horizontal liquid surface. Do not take a reading if the hydrometer is touching the side of the hydrometer jar.
Taking the Temperature
  • Using a suitable thermometer, take the temperature of the liquid immediately after taking the hydrometer reading.
  • If there is any chance of a change in the temperature of the liquid it is safer to take the temperature both before and after the hydrometer reading. A difference of more than 1°C means that the temperature is not stable, and the liquid should be left to reach room temperature.
  • If the temperature of the liquid is not the same as that on the hydrometer scale, the hydrometer reading should have a correction due to temperature applied.
Handling the Hydrometer
  • The hydrometer should never be held by the stem, except when it is being held vertically.
  • When holding the stem, always hold it by the top, as finger-marks lower down can affect the accuracy of the instrument.
  • Always handle with care.