Welcome to Ask Kate About Beer, in which The Takeout’s resident beer expert answers everything you’ve ever wanted to know about beer but were too drunk to ask. Have a question? Shoot it to firstname.lastname@example.org
Thank you, faithful Takeout commenter and otherworldly being President Zod, for your question.
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.
I know, this sounds like chemistry homework. But brewing is just delicious, delicious chemistry, right? Stick with me.
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 be,” says Erik Myers, director of tavern operations at Fullsteam Brewery in Durham, North Carolina. “The 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.”
He says 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,” Myers says. “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.
One brewery that does provide original gravity on its cans is Seattle’s Pike Brewing. They’re right there on the side, next to the beers’ malts, hops, IBUs, even its color, which is expressed in degrees Lovibond.
“We don’t expect that people are going to go into a grocery store and choose our beer based on its original gravity,” says Pike’s president and co-owner Drew Gillespie. “All that information becomes a package. Original gravity on its own, on an island, isn’t going to tell you much. But with everything else, it paints that picture for you.”
He says it’s in line with the brewery’s goal of providing education and information for the consumer. If you’re a homebrewer who’s geeking out on fermentation, then cool, there are details for you on a can.
“Original gravity, while maybe not quite as important as ABV or IBU, it’s that next level of what ‘What did the brewer do to make this beer the way it is?’” he says.
At the end of the day, though, he knows the vast majority of consumers are still choosing a beer based on who brewed it, and what type of beer it is.
“Your beer choice is mostly should come down to style: Are you a fan of a Tripel or a pale ale or a stout?”
Luckily, style is listed on almost every beer package—no decimal points, no degrees Plato.