Class is in session at Brooklyn Brewery at the CIA, our brewhouse and teaching facility at the Culinary Institute of America. Each month, we’ll take you inside the classroom to learn alongside the students participating in the most robust beer education of any culinary institute. You don’t have to do the homework, but you might want to do some extra reading.
A class like the Art and Science of Beer at the CIA is full of brewer jargon. Some of it may never make it outside the classroom. Not many people are going to ask about fining agents, or flocculation, or any of a number of other terms, but a handful seem to have escaped the brewhouse. One of the more difficult to pin down over the past few years is our handy friend gravity.
Gravity in beer is very different than the gravity that keeps us conveniently tethered to Earth’s surface. In beer, gravity is a measurement of how dense your brewing liquid is, taken as it transitions from wort to beer. The basic science is simple:
- Water is a given density of 1,000 kg/m³.
- Sugar is more dense than water. So when a given solution has dissolved sugars within, it will be more dense than water.
- Alcohol is less dense than water. So when a given solution contains alcohol, it will be less dense than water.
We know from beer basics that beer is created when sugar is converted to alcohol by yeast cells. By measuring the density of the wort before this conversion, then measuring the density of the beer it becomes, we can establish the change in density and use that to find out how much of the sugar has been converted to sweet, sweet alcohol, which is usually expressed as Alcohol By Volume (ABV.) See, science can be fun!
Many brewers use a floating hydrometer to test for gravity. A test before fermentation establishes a baseline, called original gravity. A high original gravity (or OG) will mean a beer with more alcohol, since it contains a high amount of sugar. Samples are pulled throughout fermentation to keep track of the yeasts’ work as it toils to make our beer. Once fermentation is complete, the final gravity is obtained to complete our equations. At that point, someone responsible writes it down, and the rest of us get down to the drinking part.
This all sounds well and good, except for one final hurdle for the responsible person: what measurement should be used? In specific gravity, pure water registers as 1.000. A 5% ABV beer will usually have an OG around 1.050 and a FG of 1.010. On the other hand, the Plato scale uses a system of degrees calculated using weight as a basis of density. A typical 5% ABV beer will usually register an OG around 13 degrees Plato and finish around 2 degrees Plato . Generally speaking, homebrewers rely on specific gravity, while professional brewers stick to the slightly more accurate Plato scale.
While gravities are primarily useful to brewers, drinkers may sometimes benefit from taking a look at the numbers as well. A high gravity beer will obviously result in a stronger beer. But as you compare the numbers, you can also get an idea of how dry or sweet a beer may be as well based on the change during fermentation. Remember, the more sugar that is converted to alcohol, the drier a beer will feel in your mouth. For sparkly saison and the like, this is excellent news. For sweeter beers, like milk stouts and others, unfermentable sugars may be introduced to keep more of that richness in the beer. But those sugars are a story for another time.
Whether you’re a brewer, a drinker, or a general chemistry geek, take a look at the gravity of your beer the next time you go for a drink. Just make sure you know your audience before you start lecturing about density measurements. Your author has learned– repeatedly– that most people don’t want to hear about the hard science while they’re out for a casual drink. At that point, and at most times, what’s most important is that it just tastes good.
Any questions? See us after class on Facebook or Twitter and we’ll answer any questions we can to further your beer knowledge.