|Original Gravity, also called starting gravity, could be a great band name or sci-fi series title or emo LP. In the
context of beer, though, gravity is a measurement of how much sugar is dissolved in a liquid, expressed in terms of
its density relative to water. Pure water has a gravity reading of 1.000 (at 4ºC, but let’s not get too complicated
here). So anything with a gravity over 1.000 is denser than water; anything under 1.000 is less dense than water.
Because of the precision involved in these measurements, the numbers are almost always expressed as a four-
digit figure. An original gravity of 1.080 would be read aloud as “ten-eighty.” That gravity can also be expressed on
a Brix or Plato scale, yielding readings of 19.31 Brix or 20ºP.
To understand why gravity readings matter, we need to understand the basic process by which beer is fermented.
Before yeast are introduced in the brewing process, beer isn’t really beer. It’s a sugar-water mixture called wort—
most unfortunate naming, there—which the yeast will later feast on. The measure of the density of that wort is
original gravity. After fermentation, there are generally fewer sugars left in the final beer, the yeast having done
their work to convert them to alcohol and carbon dioxide. The measure of the density of the beer post-
fermentation is final gravity.
Basically, gravity measures how much sugar was in the wort to begin with, and how much was left after
fermentation, via the liquid’s relative density to water.
These measurements mostly matter to brewers themselves. They’re helpful in terms of ensuring consistency from
beer batch to beer batch, and for determining whether a strain of yeast is doing what it’s supposed to be doing. If
a brewer started at a certain gravity, then pitched their yeast, and the final gravity reading hadn’t dipped much,
they’d know there was something wrong going on during fermentation. Maybe lazy yeast? Get it together, yeast.
Most breweries don’t list OG or FG on their cans or bottles for fear of confusing people. After all, look at how long
it took me to just give the most basic overview of what gravity is.
For the casual drinker, though, are these figures actually important? It can be interesting and can certainly give
you an idea of how sweet or dry a beer will beThe higher the OG, not only the more alcohol in the beer, but the
more residual sugar there will be in that final beer. I’d put it at the same level as IBUs (international bittering units).
They’re good indicators, but are they important to know? No.
If you want to know whether a beer is going to be sweet or dry, there’s a much simpler number you could look
at: alcohol content. There’s going to be more residual sugar in a high alcohol beer than a low alcohol beer,
So if it’s 12% or 14% alcohol, you can bet it’s going to be a candy bar of a beer.Of course there could be
exceptions to this, but generally it’s much easier to look at a beer’s alcohol content than it is to find out its gravity
readings. If you know you like big, chewy, sweet stouts, you could look for beers with a higher original gravity.
And if you don’t like those, you’d be looking for something with a lower original gravity.
Hope you found this month's column of interest. If you have any questions about beer or brewing
or just want to submit a word for me to discuss here just e-mail it to me.
Thanks and Cheers!
|OG - Oh My!
|A new column by
|Jack O'Reilly attended the
famous Siebel Institute/ World
Brewing Academy in Chicago.
|I'm very excited to be part of the BeerNexus team. I think my many years in the
beer business both as a brewer and manger will enable me to explain and
investigate many topics of interest for those who really love craft beer.
Hope you join me every month.
More by Jack: #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11,
#!2, #13, #14, #15, #16, #17, #18, #19, #20, #21