Pouring ketchup (catsup)
The full technical explanation
Let's look at the most common wrong way to do it. The bottle is held upside down, then the hungry diner waits... and waits. Most people I know attempt to improve on this by tapping the bottom. That may help, but not necessarily for the reasons you imagine.
In order for the ketchup to emerge, air must enter the bottle ... the sauce is thick enough that the gravitational pull on the ketchup does not suffice.
In the case of a partly empty bottle, tapping the base can expel some ketchup without the need for air to enter. This is because the air that is already inside the bottle can slightly de-pressurize. Tapping the inverted base may slightly liquify the ketchup, enough for some to drop out even though no air is taken in.
But in a full bottle, the ketchup must move to the side so that the air can rise through the neck at the same time that the ketchup escapes.
So, in the case of the full ketchup bottle, the problem can be divided into two issues:
- How can I get the ketchup to move aside, so that air can enter on the opposite side?
- How can I give the ketchup "extra weight," so that it will be pulled out of the bottle faster?
The first issue is solved by holding the bottle sideways, with a slight downward tilt, rather than upside-down. In this position, the ketchup naturally is pulled to the lower side of the neck, and the air naturally will channel along the higher side of the neck.
It is necessary to "increase the weight" of the ketchup by applying some G-force. This can be done by making a fist, and tapping the bottle downwards against the fist, to bring the bottle to an abrupt halt.
Striking the bottle at the upper side of the neck is much less effective, since it applies the G-force in the wrong direction.
Footnote: A year after I posted this page, I happened to be in the same pub where I first got the idea to write about pouring ketchup. At a nearby table was a couple, who had ordered hamburgers. After the woman failed to get ketchup out of the bottle by using the various wrong ways shown above, the man showed how to do it the right way. The only difference is that he bumped the bottle against his open palm, rather than against his clenched fist. (That's a better idea, but I didn't have a graphic image of an open palm.)
I asked the man where he had learned the right way to get the ketchup. He told me that he learned it while stationed in Germany (U.S. Army) around 1985. I didn't think of asking whether he had learned it from the Army, or from the Germans.
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