Monday, 15 March 2010

The science in the (kitchen) cupboard

Photo of flying pop-corn

It is interesting that when people want to describe something complex they refer to it as "rocket science". On those grounds, I guess introducing oneself as a "rocket scientist" (or as an aerospace engineer) in most social occasions would cause plenty of heads to turn to oneself. Now, I wonder if introducing oneself as a "food scientist" would have the same effect.....

I admit - I've never tried it. But my gut feeling is that "food science" scores really low on the coolness scale most people maintain. And that is totally unfair!

Food science is not an isolated island in the sea of knowledge. Instead, it would be better described as a large group of islands: food science is about chemistry, physics and biology applied onto systems of considerable complexity. I know. It doesn't sound convincing. So let me give you a couple of simple examples:

Example 1: Pop-corn physics. You know the story: You take dry corn seeds; you throw them in a saucepan with a bit of oil; you warm the saucepan; after a while the corn seeds violently explode into yummy white-ish flakes. So what has happened? Well, basically, two things have happened: Firstly, the water inside the seed turned into steam, which, with when heated up to about 170-200 oC, it raises the pressure inside the corn seed to very high levels, until the seed hull finally breaks with a explosion. Secondly, the starch inside the corn seed changes it structure to a higher volume "jelly" form. When the seeds explode, the water steam - starch mixture breaks loose and rapidly expands; at the same time, the steam escapes to the atmosphere leaving back the familiar, starch-made, foamy structure that we call pop-corn.

Example 2: Corn flour physics. Corn flour is a rather popular ingredient. In cooking, water-dispersed corn flour often functions as a thickening agent, which, when warm is thin-flowing, but when it gets colder it assumes a jelly-like behaviour. Kids are a bit more familiar with the corn flour slime, which, is unarguably considerably more fun: Just slowly start adding corn flour to a bowl with a bit of water, while stirring to ensure homogeneity; once you reach equal amounts of water and corn flour, the mix will become thicker; keep adding corn flour slowly and you will reach a point (which depends on the type of corn flour you use and the temperature), where the mix will be changing to a "solid" form under rapid stirring and melting back to the liquid form when the stirring stops.

Why that strange behaviour? Well, corn flour contains a lot of corn starch. Starch is carbohydrate molecule, comprised by lots of glucose molecules linked together, forming a long chain. Starch chains also feature smaller glucose chains (branches) attached onto the main chain. When in solution, the neighbouring starch chains can interact with each other. At a certain starch concentration, stirring or agitating the solution helps the individual starch chains hit and -briefly- stick to a high number of nearby chains, thus creating solid-looking blobs of starch. When the agitation stops, the chains go back to their original, "untangled" state, thus giving the solution its liquid-like look.

Corn-starch solutions are non-Newtonian fluids, which at certain starch concentrations behave as rheopectic (shear-thickening) ones. As you may suspect, depending on the corn starch solution and the agitation frequency, a number of cool effects can be seen. Check out the video below:

Beyond plain fun, fluids with such properties have a wide range of practical applications, from power transmission in mechanical systems to enhanced performance in bulletproof vests (traditionally employing polymer fibres).

I guess that the humble corn flour doesn't look that naive anymore, does it?


1 comment:

Andrea said...

What an awesome world is inside, above and under food...! You're right, it's unfair not to be in the top grades of "cool sciences".
Some argentinians scientists wrote an educational book called: "The cooker, the thief, his wife and her lover" ( playing with a film´s name): science in the kitchen. And in a very funny way they explain this kind of phenomena.

I write you this, while Chalilo is starching at me...sorry, staring at me...! Isn´t it all a matter of starch? Buenas noches!