Pousse-Café is, in fact, an entire category of drinks. You've likely seen them even if you didn't know what they are called. Instead of mixing or shaking liquids into a consistent emulsion, one layers them, one on top of the other. The end result, executed properly, looks like stripes - or more accurately, disks - in the glass. Obviously, it's a cool party trick worth learning.
I got my recipe from The New Craft of the Cocktail by Dale DeGroff, a relatively new book on my shelf. DeGroff suggests grenadine, crème de cacao, maraschino liqueur, orange Curaçao, crème de menthe and cognac added to the glass in that order. Six ingredients felt rather ambitious for a first try at this technique but what the hell.
Attempt #1
For the first try, I went with a martini glass. To accomplish the layering, you pour over the back of a spoon and/or down the side of the glass. I figured the slope of a martini glass would be reasonably forgiving.
While the slope of the glass definitely helped. I can see now that while physics worked for me, geometry brought obvious (in hindsight) drawbacks. Each successive layer is more narrow.
The last photo above was taken after I added the crème de menthe. So, there should be a green layer on top. That bit didn't work. However, one can see from this shot that the green layer is there, just not on top:
Here's the final product from attempt 1.
As you can see, there are distinct layers, just not six of them.
Attempt #2
For the next attempt, I used a champagne flute:
I'd say it went pretty well until, once again, I got to the crème de menthe:
The physics was falling apart but I couldn't immediately understand why. Sometimes, setting a problem aside for 24 hours, then coming back to it is just the thing...
Attempt #3
Successful layering is dependent on liquid density. A liquid with more sugar and less alcohol than another is more dense. Taking advantage of this physical reality, one can, with care, layer one liquid on top of the other without their automatically combining. That's why, in DeGroff's recipe, you start with the grenadine: zero alcohol, tons of sugar, high density. DeGroff's recipe includes specific brands for the Curaçao and crème de menthe which I didn't have. I charged ahead assuming that one brand's density would be approximately the same as another.
I was 100% wrong.
I took a closer look at the actual bottles I was using and put them in order of alcohol content. The Curaçao and the crème de menthe were the same, which explained why they were combining rather than separating. One of them had to go. I chose to keep the Curaçao as mint was the overwhelming flavor of the first two attempts and I wanted the others to have a fighting chance. So in order of decreasing density for my third try: grenadine, Curaçao, crème de cacao, maraschino liqueur and Cognac.
I also chose a more flared champagne flute for the job. In hindsight, I wonder why I didn't use it for the first attempt but I suppose I was more focused on other factors.
I was much happier with the result. The distinction between the red of the grenadine and the orange of the Curaçao is admittedly difficult to see in the photo but it's there. For color contrast, the crème de menthe would have been the better choice. But in the end, I was able to successfully create a layered drink.
I don't know how much I'll play with this concept. The end result is awfully sweet, generally not what I'm after. My wife is also a lot less impressed by this particular parlor trick than I am so I won't be getting much encouragement from my most loyal customer. But I'm glad to know it can be done, even by me.