Last week, Anheuser-Busch announced a plan to sponsor research aboard the International Space Station to learn how to someday serve beer to astronauts on Mars. This is a dumb plan---not because beer is bad, or because astronauts responsible for settling the red planet won't deserve a brewski at the end of a sol. It's just, why beer?
Distilled spirits---liquor---has always been a better fuel for exploration, or at least for explorers. Think English Navy grog: The higher alcohol content means it doesn't spoil, and it's compact. But because even the most generous launch manifest won't stock enough booze for years-long settlement missions, astronauts are eventually going to have make everything from scratch. Liquor comes from ingredients that astronauts have already grown in space. Fermenting and distilling the stuff in the cramped, zero-gravity, one-bad-chemical-reaction-and-oh-dear-god-you've-blown-a-hole-in-the-hull conditions on board a spacecraft would be tricky, sure. But if we can put a person on the Moon, well....
You probably know that potatoes become vodka, agave becomes tequila, and corn becomes moonshine, and that all of the above eventually become bad decisions. Astronauts making space booze will have to grow their own raw material, which will probably be less dependent on what they prefer to drink and more a matter of how easy the plant is to grow---and how many plants they need to harvest to get enough surplus to turn into booze.
"The whole liquor-making process is about reduction in volume," says Kris Berglund, chemical engineer at Michigan State University who is obsessed with liquor-making, and also owns his own corn farm that he uses to make his own whiskey. "If I wanted to make a gallon of alcohol, it's going to take me something like 13 pounds of starch. Corn is 60 percent starch, and there's 56 pounds in a bushel of corn...." Moral of that back of the napkin exercise: Berglund says it would probably take about 1/300th of an acre of corn to make a gallon of whiskey. That's about the surface area of a mid-sized American car, a big ask aboard a space ship or Martian colony. "Rice might be better, in terms of both the amount of carbohydrates you make per unit of area, and the fact that you can sustain it in an aquaculture rather than trying to maintain soil," Berglund says. Soju it is. Or maybe the crew has less discerning tastes. In that case, they can make their mash from any starchy, veggie, or fruity food scraps.
Before the Marshiners can ferment, they'll need to supplement their mash with sugar---yeast needs the sweetness in order to excrete alcohol. On Earth, liquor-makers create the right kind of sugars in a sticky, messy, time-intensive process called malting, where they let the plant matter sit in warm water until it sprouts. Berglund suggests the astronauts take advantage of recent innovations by places like White Labs, which have developed special yeasts that excrete sugary enzymes all on their own.
After harvest, the astro-farmers will have to render the starchy parts of the plant matter into a mush and douse that with yeasts. Fermentation is the same no matter if you're making beer, wine, 18-year scotch, or Mad Dog 20/20: Yeasts eat the plant's sugar and excrete ethyl alcohol. This can be messy, and typically requires a lot of space---not as much as growing the plants did, but probably enough to throw off the feng shui in the kitchen module.
But this hypothetical space mission is already a committed little moonshinery, so the real problem will be keeping the yeasts alive and happily churning out alcohol in microgravity. Not that the yeast themselves would likely be affected by gravity one way or the other---they are single-celled organisms, and probably barely notice the subtle tug on Earth. Rather, gravity governs the conditions of the the sloppy medium in which the yeasts live. "If there is too little pressure on the outside of the yeasts, they will just blow up," says Berglund. The solution here is probably something mechanical, like a motor that spins the fermenter just enough to create centripetal force. Luckily that kind of machinery already exists in breweries here on Earth.
A still requires everything you do not want on a spaceship---fire, high pressure, steam, chemical fumes---and the one thing you can't have without breaking the laws of physics: gravity. "It would be quite hard, as the whole principle of the thing revolves around the fact that the alcoholic vapor goes up and the liquid phase remains down," says Matthew Pauley, a distilling researcher at the International Centre for Brewing and Distilling in Edinburgh.
The first problem is somatic: liquids in low gravity form spheres. Train your ball of fermented plant mush to behave inside a still is just the beginning. Alcohol has a lower boiling point than water, so in typical distillation, liquor makers heat the still so the alcohol boils but water stays mostly liquid. The alcohol rises up a column as a boozy vapor, and the distiller uses a condenser to cool the boozy steam back into a liquid, which gets shunted over to a connected vessel called an alembic. "As I understand it, and I by no means an expert in the field of zero gravity fluid dynamics, it appears that the usual model of convection currents and nucleating boiling that we know and love on Earth is no longer valid."
This doesn't mean they scrap the whole operation. Distilling is just one way to make liquor. "If you're willing to think outside the box, you can make spirits with no distillation at all," says Berglund. By box, he means spaceship. Remember when Ripley opens the cargo bay doors in Aliens and relies on the vacuum of space to suck the queen into inky, eternal night? That happened because of the pressure differential between spaceship and space. The same principle could be used to perform something of a reverse osmosis on an aspirant spirit. Put the pre-separated liquid in a vessel on a pressurized spacecraft module, and an empty vessel in a non-pressurized adjacent module, with a membrane between the two. Then let equilibrium take care of the rest. Best of all, without all the heat and fumes from the distiller, the most dangerous part of the alcohol process would be what happens when you drink too much. In other words, exactly the way things are on Earth.
