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Ketchup meets science

How do you get the right amount of ketchup to flow out of a glass bottle – without blobbing! Scientists from the University of Melbourne have tackled this question.

 

Ketchup has a special consistency. It is not liquid. Instead, it is a “soft solid”, explains Dr. Anthony Stickland. The sticky mass contains tomato pieces, which touch each other and form a kind of network. It takes a certain amount of force to make ketchup flow. Experiments have shown that the optimum flow speed is 0.045 km/h or 0.028 miles/hour. That is 1.25 cm per second or 0.5 inches per second.

What is behind the ketchup-pouring phenomenon?

Liquids such as water flow faster the more pressure is exerted on them. With ketchup, peanut butter and mayonnaise it’s different. Once they are moving, the viscosity drops rapidly at a certain point. Physical scientists call this “structural viscosity”. At very high speeds, the viscosity can be similar to water. Then it can easily happen that the ketchup spills uncontrolled out of the bottle.

 

The scientists have developed a method by which you can pour ketchup onto your plate without splattering: First, shake the bottle thoroughly – with the lid closed – so as to mix liquid parts with solid particles. Then stand the bottle on its head – still closed – to let the sauce flow towards the bottleneck. If the bottle is nearly empty, you’ll need more momentum than with a full bottle. Now it will only take a little force to pour the ketchup out. Stand the bottle right way up, take off the lid and tip it over immediately again. With a full bottle, the weight of the sauce is enough to get it flowing.

More tips & tricks

If this fails, you need dexterity. Hold the bottle so that opening points at your plate at a 45° angle – one hand on the bottleneck, the other on the bottom. By gently knocking or shaking, the force can be increased little by little until the sauce starts to flow. In this way, ketchup can be tamed with just a little bit of physics. Another popular solution is to stick a knife into the bottle. This reduces the viscosity of the ketchup at the opening and a certain amount is detached.


The groundbreaking discovery for enjoying splatter-free ketchup may interest fans of practical physics. The applicability to the kitchen is up to the individual reader. And whether the Australian scientists are still working on this phenomenon is another story.


Source: Heike Kreutz, Harald Seitz, www.bzfe.de