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Ketchup (the tomato variety) is a thixotropic substance, which often results in difficulties of removing it from a glass bottle. Often a glass bottle will appear to be blocked. The "common" method (inverting the bottle and hitting the bottom with the heel of the hand) can often cause the ketchup to suddenly gain enough momentum to begin flowing, and due to the shear stress on a thixotropic substance, lose viscosity, and therefore flow even more, causing a significant amount of ketchup to flow out of the bottle. Some people, seeking to avoid this problem, remove the product with the aid of a butter knife thrust into the opening. But this technique is generally slow and inefficient, and can potentially contaminate the ketchup.

There is a better technique that avoids both the thixotropic effect and the need for an inefficient tool. Known widely among caterers, it involves inverting the bottle and forcefully tapping its upper neck with two fingers (index and middle finger together). Specifically, with the Heinz Ketchup product, one taps the 57 circle on the neck. This helps the ketchup flow by applying correct G-forces. Another solution to this problem appeared with the introduction of plastic squeeze bottles. More recently, Heinz and others have introduced an "upside-down" bottle, which further remedies the problem by keeping the remaining ketchup at the mouth of the bottle. These bottles are also fitted with a control valve in the nozzle designed to eliminate the build-up of ketchup in the cap after use. This, however, leads to squirt control problems.

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