A conversation that bubbled up at the dinner table last night, some time after the Free-Ride offspring were informed that the cassoulet they were eating had, as one of its ingredients, white wine.
Younger offspring: Why do they call booze "spirits"?
Dr. Free-Ride's better half: I think that goes back to the early days of distillation. Do you know what distillation is?
Elder offspring: Ummm...
Dr. Free-Ride's better half: OK, to distill something, you have a container of the thing it is you're distilling. You apply heat to that container, and it's attached to a tube that's usually surrounded by something like cold water. As you're heating the stuff in the container, some of it turns into vapor, and when the vapor gets into the tube surrounded by the cold water it cools down --
Elder offspring: And condenses?
Dr. Free-Ride's better half: Yes! And that tube where the vapor is condensing is hooked up to a collection container, so it drips down into that container instead of going back to the container with the original stuff you were heating.
Younger offspring: I still don't understand what this has to do with "spirits".
Dr. Free-Ride's better half: Well, using this distilling, you could take a substance that looked pretty muddy and yucky and still collect distillate -- that vapor that condensed -- that was clear. So people thought that the clear liquid they could collect was the "spirit" of the muddy, yucky stuff.
Younger offspring: Oh.
Dr. Free-Ride: Of course, you can also distill stuff that isn't muddy and yucky. For example, you can distill wine to make brandy.
Younger offspring: But brandy is brownish.
Dr. Free-Ride's better half: That's because it's been aged in oak casks after it's distilled.
Elder offspring: So, do they use distillation to make beer and wine, too?
Dr. Free-Ride: Nope. You make beer and wine and hard cider --
Dr. Free-Ride's better half: And sake!
Dr. Free-Ride: -- and sake through fermentation.
Younger offspring: Huh?
Dr. Free-Ride: Fermentation happens when yeast in your grape juice or apple juice or grain munch on the sugars and make alcohol.
Elder offspring: Oh yeah! The yeast eat the sugar and they poop out alcohol and carbon dioxide?
Dr. Free-Ride's better half: What they do actually depends on whether they have a lot of oxygen around. So, why are the yeast eating sugar?
Younger offspring: To get energy.
Dr. Free-Ride's better half: That's right. And in conditions with plenty of oxygen, the yeast will get a lot of energy out of the sugar and give off carbon dioxide as a waste product. But when they're deprived of oxygen, they can still get energy out of the sugar -- not quite as much, but they manage. And then, they give off alcohol as a waste product. Here, let me show you. (writing on some scrap paper)
Dr. Free-Ride's better half: Sugar -- well, glucose, anyway -- has six carbons and a bunch of hydrogens and oxygens. And in grape juice or apple juice there's plenty of H2O around. So, if the yeast have lots of oxygen to work with, how many CO2 can they make from each sugar?
Dr. Free-Ride: Just think about the carbons here ...
Elder offspring: Six?
Dr. Free-Ride's better half: That's right. OK, and here's alcohol -- the kind we drink is actually ethyl alcohol --
Dr. Free-Ride: Which nowadays we call ethanol.
Elder offspring: Hey, don't some cars use that for fuel?
Dr. Free-Ride: Yes.
Dr. Free-Ride's better half: -- which has two carbons, six hydrogens, and an oxygen. So if the yeast don't have access to lots of oxygen as they're eating their sugar, how many alcohols can they make from each sugar?
Elder offspring: Umm, three?
Dr. Free-Ride's better half: That's right. Now here's what's interesting: just with fermentation, the alcohol level can't get very high. Do you know why?
Younger offspring: The yeast find oxygen?
Dr. Free-Ride's better half: No. Alcohol is a poison.
Younger offspring: It is?
Dr. Free-Ride: Uh huh. And that means, once there's a certain level of it floating around in the juice where the yeast have been munching the sugar --
Elder offspring: It poisons the yeast?
Dr. Free-Ride: That's right. They're swimming in their own waste products and after a certain point, those waste products kill them.
Elder offspring: Kind of like us swimming in our own waste products as the planet gets more and more polluted.
Dr. Free-Ride's better half: Um, yeah.
(There followed a brief interlude in which the Free-Ride offspring made their best gruesome "yeast poisoned by its own waste products" faces. They were pretty gruesome.)
Dr. Free-Ride: So, if fermentation only gets you to the concentration of alcohol that kills the yeast, distillation is a way to get a higher alcohol concentration.
Younger offspring: Distillation makes alcohol, too?
Dr. Free-Ride: No, the yeast make the alcohol, but distillation lets you concentrate it by separating it from the water. And the reason you can do that is, as you're heating what it is you're going to distill --
Elder offspring: Like wine?
Dr. Free-Ride: -- like wine, is that the water in the wine and the alcohol in the wine boil at different temperatures. The alcohol doesn't need to be quite as hot to turn into vapor, so it goes up into the tube to condense and be collected before the water really gets boiling.
Younger offspring: And then you get more alcohol?
Dr. Free-Ride's better half: Nope, it's the same amount of alcohol you started with before you distilled it. You've just separated it from a lot of the water.
Elder offspring: And other muddy, yucky stuff.
Dr. Free-Ride: I will thank you not to refer to wine as muddy, yucky stuff.
Younger offspring: So yeast make alcohol.
Elder offspring: And distillation can separate alcohol from other stuff.
Dr. Free-Ride: And you children make really scary dead-yeast faces.