What is Original Gravity?

by Karl | Last Updated: May 13, 2020

How are you making your beer? The art of making beer is more than just that. It is a science. If you are a connoisseur or even a home brewer, you wish to have the alcohol content just right.

And you do not want to be stumped when the receiver asks you about the alcohol content of your concoction.  How much alcohol are you drinking?

It is very important to measure the alcohol percentage in your beer, especially when you are making that for commercial purposes. It might appear to be a complicated idea, but when the basic terms become clear, the entire math becomes simple and formulaic.

What is Original Gravity

ABV or Alcohol by Volume

The first among the important terms is Alcohol by Volume abbreviated to ABV. It is how the alcohol percentage in the beer (or any alcoholic beverage) is expressed. Typically, beer falls between the ABV range of 3.0 to 13.0 percent. This is the amount of ethyl achohol present in the beer. To arrive at this we need to have certain other figures.

The beer-making process begins with the extraction of the wort (pronounced “wert”) from the original herbs. The wort is the liquid that contains the sugars that shall be fermented eventually during the process. This process is carried out in the lauter tun which is a vessel like a colander that sieves the liquid from the mash of malted barley.

Original Gravity Reading

The wort then has to be measure for its gravity. The gravity refers to the wort’s density relative to water. The density of water for this process is taken to be 1 kilogram per litre. The calculation of the density of the wort will provide you with the answer for the potential strength of your drink. This measurement of the gravity of the drink before fermentation is called Original Gravity.

To calculate the ABV, we will have to deduct the Final Gravity from the Original Gravity that has to be measured at the end of the fermentation process and then substitute the value in a formula for the same.

Knowing the Pound per Gallon

Even before figuring out the original gravity, we have to calculate the Points per Pound per gallon or PPG of each ingredient that shall be included in the beer. This gives us an account of the specific gravity of the ingredient when one pound of it is mixed in one gallon of water.

Original Gravity – Final Gravity (OG – FG)

To measure the Original Gravity of the wort, two basic instruments are readily available. It is important to understand that both are susceptible to inaccuracies and will only be able to provide an approximately correct density which should be enough for a small brewer.

Using a Hydrometer 

The first instrument is a hydrometer which is a small thermometer-like instrument which has to be dipped in a vessel containing 130 millilitres of wort. You can read the scale of the hydrometer to quickly know the gravity of your drink. Here’s an in-depth look at how to read a hydrometer correctly.

Using a Refractometer 

The other instrument is a Refractometer, which is generally used because of its better accuracy. This is an instrument with a glass prism at the end of it on whose surface only a few drops of the wort are enough to give the reading of the density in degrees Brix (Balling and Plato are the other scales).

Note that both the before and after readings on these instruments be taken under approximately the same temperature else the readings would be slightly skewed.

This done, now the wort whose original gravity reading has been taken is then placed in the Fermenter Tank where it is fermented by the yeast. When the beer is ready, we need to take the Final Gravity reading with either of the instruments mentioned above. The final reading would show us how dense the drink finally is after all the sugars have been fermented.

What’s the mathematical equation?

Once the original and final gravity have been calculated, it is very simple to determine the Alcohol By Volume. The formula for ABV is:

ABV = (OG – FG) x 131.25 (Where OG stands for Original Gravity and FG stands for Final Gravity)

The above is the universally accepted formula, but a more accurate one has come into popular usage for professional brewing:

ABV = (76.08 x (OG – FG) / (1.775 – OG)) x (FG / 0.794)

So, if your OG is 1.050 and the FG is 1.010, using it in the first formula we get an ABV of 5.25%

Applying the second formula we get roughly 5.38%, which nears the accuracy mark.

Try these handy Specific Gravity, Brix, & Plato Conversion Calculators.

What does the most popular beer have?

America’s most popular beer by Guinness checks out at an ABV of 4.2% which is in the middle of the range. While Bud Light, another popular commerical beer has an ABV of 5%.

The world’s strongest beer is called Snake Venom which has a whopping 67.5% alcohol content. Created in a Scottish Brewery, this is quite literally a venom that can disarm you within seconds of intake. Appropriately named.

Having the right temperature

To understand this concept, you need to keep in mind that temperature is a big factor which can change the readings of the gravities quite a bit. You should be relatively confident of your ABV before you market or even recommend your beer to a friend not just because of the market regulations, but to ensure that people remain aware of when and how to enjoy it.

Misinformation can be potentially dangerous for the person who cannot see the effects of a particularly inebriating brew coming. Ensure correct information is conveyed on your homebrew labels and enjoy knowing your numbers. Cheers!

Lead marketer, brewer, dad, and husband. Pretty much an all-round awesome guy.