Oregon ducks
One of the things that I enjoy about brewing is watching the process. Beer is alive. At the most basic level, you’re creating a big bucket of yeast food, throwing in the yeast, and watching it eat. When the yeast gets going things get spectacular: the solution heats up and roils violently, the surface foams and bubbles, and the carbon dioxide gassing off can bear all sorts of aromas.
These cues help you track the progress of fermentation but they’re also just fun. It’s like having sea monkeys but they make you beer.
I’m in Oregon this week visiting my parents, so I’m not able to watch the show. But I have two ways to continue to keep tabs on it while I’m gone. If you don’t brew, I thought it might be interesting to read about some of the chemistry and tech. If this isn’t interesting: please move on!
Tilt Hydrometer
Hydrometers measure the density—or “specific gravity”—of a liquid (technically, the amount of dissolved solids in solution). Pure water has a specific gravity of 1.000.
The brewing process starts with making “wort”, which is basically a sugar solution. Sugar is heavier than water, so wort has a specific gravity higher than 1.000—typically 1.040 or higher. The more sugar, the higher the specific gravity.
In fermentation, yeast eats sugar and turns it into alcohol and carbon dioxide. Alcohol is lighter than water, so as the beer ferments, its specific gravity decreases. By measuring the amount the specific gravity has decreased, you can calculate how much alcohol has been produced. That’s the basic math.
Tilt Hydrometer
The Tilt Hydrometer is an integrated set of sensors—accelerometer, thermometer, low-power Bluetooth—in a plastic capsule that you drop into your fermenting beer.
It’s heavier at one end and not evenly balanced along its long axis—if you hung it on a string from its center of gravity, it would be tilted. It’s this trait that allows it to measure the density of the beer—the denser the solution it’s floating in, the more tilted the angle at which it’s floating.
Every 5 minutes, the accelerometer computes the specific gravity based on the angle and transmits it via bluetooth to—in my case—a raspberry pi I’ve set up as a bridge to the internet. The Tilt folks have provided software that logs the info onto a Google sheet.
This all means that I can watch my beer ferment from Oregon! Here’s what the graph for my Double IPA looks like:
Double IPA Fermentation Graph
So how do I read this? The blue line is the specific gravity. I put the Tilt in the DIPA on 13 September—at that point the specific gravity was 1.051. Fermentation was furious through 15 September, at which point the gravity had fallen to 1.020. After that, fermentation slowed—we’re tending down to 1.015 as of today. This translates into an ABV of 4.6%.
What do I make of this? I was expecting the yeast to go a bit further—I’m looking for a higher ABV. The strain I used is generally supposed to ferment about 74% of the sugar—it about 8 points shy of this when I left for Oregon. Before I left, I threw a pack of Lallemand CBC-1 into the wort—this is a yeast that can handle rough conditions without creating its own flavor, adding a little oomph when other yeast has given up the ghost. We are getting additional activity, so we’ll see what happens with another week of fermentation.
The line isn’t moving a lot, but I do have other ways to monitor the activity. I’ll tell you more about that in the next post!