Ketchup (or catsup) is a thixotropic fluid made from tomatoes. The property of thixotropy is familiar to all users of ketchup, and is caused by added starch. That is to say, it becomes less viscous when agitated. This phenomenon results in the familiar scenario of overpouring ketchup when the bottle is shaken to get the ketchup moving. This vexing problem was partially solved by the introduction of squeezable ketchup bottles. For mostly empty squeezable bottles, or glass ketchup bottles, the most effective ketchup pouring strategy is this:
- Ensure the lid is firmly on
- Shake the bottle vigorously in the axial direction
- Turn bottle upside down, and open over your plate