West Coast Brewer Home Brewing Blog

Tag: brew house efficiency

Original Gravity

Original gravity or OG is the specific gravity reading of a beer’s wort prior to having the yeast pitched for fermentation. The original gravity reading is important because it gives the brewer an idea of how much sugar is available for fermentation and what the approximate alcohol by volume will be once fermentation completes. The original gravity reading also permits a brewer to calculate his or her brew house efficiency to determine what percentage of starches and sugars were extracted from the grain bill used to make the beer. Typically either a hydrometer or refractometer are used to take the original gravity reading.


Below is the photo of a hydrometer which is used to take original gravity readings.

Beer Hydrometed, Final Gravity Reading


A hydrometer is an instrument used to measure the specific gravity of liquid in comparison to pure water. The hydrometer is important because it allows a brewer to determine several things:

  • When the mash is no longer contributing sufficient levels of sugar during a sparge
  • How much dissolved sugar is in the finished wort
  • If your beer has under or over fermented
  • Brew house efficiency
  • Original gravity
  • Final gravity
  • Fermentation progress
  • Fermentation completion
  • Alcohol by volume.

Below are three examples of different hydrometers that are available to brewers, including one used for determining your final gravity.

Beer brewing hydrometers for taking specific gravity readings such as Original Gravity and Final Gravity

Beer brewing hydrometers for taking specific gravity readings such as original gravity and final gravity.


Here is the final gravity reading from a hydrometer that also registers temperature so that corrections can be made if the beer is too hot or too cold.

Beer Hydrometed, Final Gravity Reading

Beer hydrometer showing a final gravity reading.