In History of Rock & Roll, we got all cosmic, groovy and beautiful. Yeah man, it was psychedelia, mind-altering substances and love beads as we covered the period 1965-1969. Dylan goes electric. Summer of Love. Hippies. Communes. Sit-ins. Protests. Hendrix lights his guitar on fire. Sergeant Pepper’s Lonely Hearts Club Band. Woodstock. And then <sigh> the Hell’s Angels kill a spectator at Altamont as the Rolling Stones watch. In a flash, the era of flowers and free love is over. Within a year, Hendrix, Joplin, Brian Jones, Keith Moon, and Jim Morrison are all dead. The Beatles break up. And rock again teeters on the edge of oblivion. Next week, rock & roll tries to survive the 70s (and disco).
In FCF, it turns out that we are now finished with the “F” in FCF (Filtration) and have moved on to the “C”: Carbonation. Carbon dioxide is a rather stable gas at room temperature, but for commercial storage, we apply a great deal of pressure to it and force it into liquid form, which we can then store (under great pressure) in gas bottles or tanks. From there we can dispense it via a regulator to carbonate our beer.
(You can also drop the temperature or apply even more pressure–or both–and end up with solid CO2, better know as dry ice. But I digress…)
However, it turns out that as much as we like CO2 in our beer, the CO2 doesn’t like being there. It only dissolves into water because it forms carbonic acid with water molecules, and it will flee from the water if presented with an opportunity–a rise in temperature, for instance, or a drop in the pressure of the gas above the beer (such as when you pop the top on a bottle of beer).
CO2 is totally ruled by Henry’s Law: “At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.” In a nutshell, what this means is that if you hold beer under a head of pressurised CO2, some of the CO2 will dissolve into the beer. It seems that Mother Nature abhors having a lot of molecules of CO2 above the beer, and none in the beer, so over time, some of the molecules will migrate into the beer until equilibrium is reached.
However, simply putting the beer into a gas-tight tank, then pressurizing the head space above the beer with CO2 is slow. Really slow. It’s the “OMG This Is Taking So Long” method, since it can take hours or even days, depending on how much surface area of beer is exposed to the head space.
Then there is the slightly faster method of bubbling CO2 into the beer through a pipe. This may be a bit faster, since the bubbles do increase the amount of surface area touching the beer, allowing CO2 to dissolve a bit more quickly.
This method could be much faster though, if instead of making large bubbles, you produced eensy-teensy weensy bubbles, since overall, the smaller bubbles of a certain volume would have a much greater surface area than one large bubble of the same volume. That’s where a carbonation stone (or sintered stone) comes in. A carbonation stone is composed of sintered steel–steel that is fractured through and through with tiny passages and holes. If you force CO2 through sintered steel into beer, the gas emerges as a fine mist of bubbles–perfect for carbonating beer relatively quickly. The only problem is that you have to use extra pressure to force the gas through the sintered steel.
But if you’re really in a hurry, the way to go is a cross-flow system. This (expensive) carbonator has a large snake-like pipe that twists back and forth. Inside the pipe, running along the centre is a long tube of sintered steel. You pump the beer through the pipe in one direction, and push CO2 through the sintered steel tube in the other direction. The beer, as it travels through the pipe, is subject to a veritable blizzard of CO2 every centimetre of the way. By the time the beer has travelled the length of the pipe–a few seconds at most–it is fully carbonated. If you are very clever about it, you can even run your beer from the fermenter to the filter then through the carbonator and straight to the packaging line, obviating the need for a bright tank. However, getting the right flow of beer and counterflow of CO2 to produce exactly the right amount of carbonation can be tricky. In addition, if something happens and you have to bring the beer flow to a halt, even for a few seconds, the beer sitting in the carbonator gets over-carbonated and has to be dumped.
Next week, more fun with CO2, including exploding gummy bears.
Student of Beer 