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Wednesday, November 25, 1998 Published at 12:25 GMT


Sci/Tech

No more flunking on dunking

Working it out: The formula for delicious dunking


BBC News 24 science reporter Natalie Barb: Dunking enhances the flavour
Scientists have finally explained the perfect way to dunk a biscuit.

People have long had to endure lumpy tea when their favourite nibble disintegrates to form a grey sludge at the bottom of the mug.


[ image: Only a scientist could dunk like this]
Only a scientist could dunk like this
Now researchers from the University of Bristol in the west of England have published the mathematical formula that governs the whole process.

Their work is set to revolutionise tea and coffee breaks the world over, especially when a list of recommended dunking times is published.

Taste test


BBC Science Correspondent Pallab Ghosh: Different biscuits have different dunking times
The study reveals precisely why we are drawn to dunking - it seems more of the flavour of the biscuit is released into our mouths if it has first been dunked in a hot drink.

The Bristol team calculate that up to 10 times more flavour is released this way than if the biscuit is eaten dry.

Their two-month investigation has also established the best strategy for dunking chocolate biscuits. The "flat-on" approach requires the nibble to be immersed biscuit side down.

This minimises "chocolate bleed" into the tea or coffee and keeps the coating rigid enough to prevent the biscuit from breaking in half.


[ image: Mini dunk: A single grain of starch swells]
Mini dunk: A single grain of starch swells
The team acknowledge this technique requires a degree of skill on the part of the dunker and have therefore designed a prototype dunking holder to help the less dextrous.

Dr Len Fisher, who led the research, said a biscuit could be viewed as lumps of starch glued together by sugar.

When the hot tea or coffee enters the pores in the biscuit, he explained, the sugar melts and the structure becomes unstable.

"You have got a race between the dissolving of the sugar and your biscuit falling apart and a swelling of the starch grains so that they stick together, giving you a biscuit which is purely starch but rather softer than what you started with," he said.

"As with most things in physics, we can write equations which govern this."

Dunk with confidence


[ image: Len Fisher: Plans more user-friendly information]
Len Fisher: Plans more user-friendly information
In this case, the average pore diameter in a biscuit is equal to four times the viscosity of the tea, multiplied by the height the liquid rises squared, divided by the surface tension of the tea, multiplied by the length of time the biscuit is dunked.

Aware that some people may have problems with their maths, Dr Fisher plans to give people more user-friendly information.

"We are going to define critical times for different types of biscuit," he said.

"We will publish these as a table, you will be able to look them up and you will be able to dunk scientifically with confidence."


[ image: How much can a biscuit take?]
How much can a biscuit take?
Although the research is not complete, Dr Fisher believes the temperature of the tea is also critical.

"I suggest for serious dunkers, take a thermometer with you," he said.

The research has been funded by the biscuit manufacturer McVitie's.

The company says its own research suggests that one-in-four dunks results in soggy biscuit sinking to the bottom of the mug. It may now print advice for consumers on its packaging.



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