# How to make the perfect sandwich

Oh sandwiches. As much as the process of lunching might have progressed and got more sophisticated over the years, we still can't think of a better 1pm meal than two slices of bread and a delicious filling.

But despite the alarming simplicity of the sandwich, not every combination delivers the goods. Lest we remind you of the worst sandwich ever. Sorry about that.

To celebrate British Sandwich Week, those bread-making types at Hovis have teamed up with Dr Mark Hadley, researcher at the University of Warwick’s Department of Physics, who has created a mathematical formula for creating the perfect sarnie.

So, here it is:

And yes, it's going to need some explanation. “The equation governing the movement of liquid, like water on the lettuce or the juice from the tomato, is governed by the Navier-Stokes equation and this equation is the simplified form," Hadley reveals. "It becomes more complicated for a filling that can be compressed, like tuna mayo, which will flow like a liquid but with higher viscosity."

Yeah, so we're still a bit confused but Hadley's equation offers some proper scientific tips on how to avoid a bad sandwich and he's deciphered them for us here:

• Pressure: Don’t apply unnecessary pressure (the p(x,t) term) it squeezes out the water
• Freshness: The equations describe the deterioration with time due to slow diffusion of the moisture, so eat your sandwich while it is fresh
• Butter: Use a thick layer of butter, it is hydrophobic and keeps moisture away from the bread
• Moisture: Control the loss, or uptake, of moisture from the air into the bread:

- Butter protects the top

- Crusts are good; they stop the edges drying out (φair < φbread) or going soggy (φbread < φair)

- Wrap the sandwich tightly to keep air away from the underneath – but don’t squeeze it of course

• Temperature: Most equations are temperature dependent particularly viscosity and absorption rates, keep it cool to reduce the reaction rates.
• Bread: Use the right bread, a thicker slice like in Hovis British Farmers Loaf, has a greater resistance to dampness and can’t dry out so quickly either

Now go forth and make a perfect sandwich. Bringing it for us to sample is optional.

(Image: Rex Features)

## More

### A gravy bar is opening up in Manchester so of course you want to go

Why the hell not?

by Matt Tate
24 Mar 2017

### Someone has invented beer based on your DNA, to ensure you like it

We already do like it, though

by Gary Ogden
23 Mar 2017

### Richard Osman has put Jaffa Cakes in his World Cup of Biscuits

He's blown the debate wide open again

by Gary Ogden
23 Mar 2017

### Easter even caters for Buckfast lovers now

Sounds like they're racking up orders

by Matt Tate
22 Mar 2017

Thanks everybody

by Gary Ogden
22 Mar 2017

### This shop sells Liquorice Allsort and Chocolate Orange sandwiches

Is this really a thing?

by Alex Finnis
21 Mar 2017

### Cry into your caviar: Waitrose is making it harder to get free coffee

What on earth would the Queen think?

by Gary Ogden
21 Mar 2017

### Heineken are launching an alcohol-free lager

They say it'll be the best-tasting on the market

by Gary Ogden
20 Mar 2017

### 2017's worst news yet: Wetherspoon's prices are increasing

You've gone too far this time, world

by Gary Ogden
13 Mar 2017

### Giant Kinder Eggs have arrived in time for Easter

And yes, you still get a toy

by Matt Tate
09 Mar 2017