Homebrewing is full of lore and dogma: you soak it in and just take it for granted. Most things make sense as you learn the hobby, but other things are more arbitrary. Look at any recipe, from beginner to more expert, and two numbers jump out as guideposts: original gravity (OG) and final gravity (FG). The numbers themselves are anything but random, but the measurement system we use is a different story. You might have noticed a clue with your first homebrewing kit. Almost every hydrometer is marked with three scales: specific gravity, degrees Plato or Brix, and potential alcohol, but homebrewers are steered toward specific gravity as the obvious choice. Professional brewers, on the other hand, usually use degrees Plato.
Even though you can convert between the two with varying accuracy, these two systems are not quite equivalent. Let’s take a closer look and then figure out whether we should care.
Three Degrees: Balling, Brix, and Plato
From the perspective of brewing, the Balling, Brix, and Plato scales are functionally equivalent scales that were derived by measuring the density of various concentrations of sucrose solutions (the Balling and Brix scales are used more in winemaking while the Plato scale is used in brewing). In each case, the measurements got a little more precise, but the differences among them are tinier than we can detect at home. If your wort or beer has a gravity of 12° Plato, that means that the density is the same as if it were a solution that was 12 percent sucrose by weight. Even though your beer is not a mix of simple sugar and pure water, this works because we tend to focus on comparing relative density measurements.