When we say a beer is ready to go out, we mean it. At that point, we have decided that the color, clarity, aroma, flavor, mouthfeel, and finish are dialed in enough to put our name behind a beer and share it with the world. We expect to see a small degree of variation when looking at any given characteristic, but any deviation outside of imperceptible and subtle usually belongs in the drain and not in your glass. To make beer as consistently as we need to, we take several measurements as beer ferments, conditions, and carbonates. Making beer on a scale as small as we do, there are some limits to how well we can know what we need to know. It doesn't make sense for a brewery our size to invest in all the bells and whistles that New Belgium or Sierra Nevada has.
Our Zahm is like the fourth Emanuel brother. Forget saving lives, repping Hollywood's best-paid talent, and running America's third largest city; this is Mr. Emanuel's favorite.
What we do have, we absolutely need. One of those tools is our Zahm. It's a CO2 volume meter that we use to know when our beer is fully carbonated. For most beers we shoot for about 2.5 volumes of Co2. That means each pint of beer you drink isn't just sixteen ounces of liquid; it also contains the equivalent of thirty-eight ounces by volume of CO2 at room temperature and standard atmospheric pressure dissolved into it. That's a theoretical limit assuming no gas escapes between the keg and your lips. A lot does, and that's why your beer comes out with a dense, inch-thick head on it when it's stored and served properly. Some CO2 also comes out of solution on your palate, sharpening the mouthfeel, enhancing the perception of bitterness, and scrubbing away any richness from the Baked Cheetos you've been munching on. This is important to get right.
The Zahm works on the fundamental relationship between volume and pressure. We attach the Zahm to the Zwickel, or sampling valve, on the brite tank and allow the chamber to fill with beer until it flows out of the relief valve. We close the relief valve, allow the pressure in the Zahm to reach the tank pressure, then bleed off any foam. We close up the Zahm and the tank completely, open a piston on the Zahm and shake the hell out of it. The movement of the piston causes a change in volume, which has a known relationship to the pressure applied from the dissolved gas in the liquid. We take the pressure and temperature readings from the Zahm, compare them to a chart calibrated for CO2 in beer, and find the volumes of dissolved CO2. We repeat this procedure with increasing regularity as we approach the desired carbonation level, which varies by style.
As you take your next drink of Solemn Oath beer, take a moment to revel in the tiny bubbles that separate beer from uncarbonated beverages. And while you're at it, shake your head at the fact that we own a thousand-dollar instrument that operates like an as-seen-on-TV gag gift.
This is the third post in my “What’s That Thing Over There?” series in which I reveal the extraordinary and mundane of brewery miscellania. In my last two posts, we talked about how beer is like sausage and legislation and got the skinny on the troll that lives under the brewdeck. Next time, who knows? The Thing you’re wondering about may be on deck. Just please, stop asking our poor bartenders what that damn thing over there is.