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Why?

Techly Explains: Why does food turn brown when cooked?

Humans are unique in the animal kingdom – most of us can count the times we’ve seen a dog cooking up a nice slab of steak or toasting a baguette on one hand.

But whereas a cute pupper is wont to gobble up any food in front of it without hesitation, impatient, lazy humans are more likely to spend our time in front of the stove thinking about life’s most important questions – namely, “why the hell do I have to heat this stuff up for so long before it actually tastes good enough to eat?”

Chemists refer to the carrying out of these reactions as ‘cooking’, and the similarities between the worlds of the chemistry professor and the culinary expert go a lot further than Walter White occasionally using the word ‘cooking’ on Breaking Bad.

Most of the changes that occur in the production of food, from taste to texture to appearance, are usually do to the altering of the food’s chemical properties.

When it comes to cooking food, then, the change in taste that comes with the shift to a dark brown colour after cooking is known as the Maillard reaction, and it’s responsible for a wide range of different flavours that appear when produce hits the pan.

So how does the Maillard reaction work? Most people are familiar, at least by name, with amino acids. Put simply, amino acids are the basic units that make up proteins, and are essential for a whole host of biological functions – and, as a result, are almost ubiquitous in food.

In the presence of heat – roughly 140 ºC to 165 º C – the amino group of the acids reacts with the particularly reactive carbonyl group present in sugars, another common, biologically-active class of molecules.

The products of this reaction produce new flavours and smells.

Depending on which amino acids and sugars are involved – and there are a whole lot of different kinds of both of those around – as well as the stability and subsequent breakdown of the product formed, a whole host of different smells, tastes, and combinations can form.

In fact, there are so many possibilities that scientists are having a hard time cataloguing all of the different arrangements, as most foods contain fairly unique combinations of amino acids and sugars, and subsequently, have subtly varied tastes upon cooking.

The range of possible tastes that can be produced by utilising this reaction has been one of the main tools in the production of artificial flavours and smells for decades. It proceeds faster in more alkaline environments too, which is why lye is added to pretzels in order to darken them.

The Maillard reaction is responsible for the crust on bread, the colour of a well-done steak, and the texture of a roasted marshmallow. It’s a cornerstone of human biology – it happens within the body on the regular as well.

So next time you’re bored at the stove – or, even more incredulously, bored watching a dog fry up some nice dumplings – comfort yourself with the knowledge that every bit of cooking you do is probably more of a chemistry experiment than you ever realised.

Aren’t you a smart cookie?

About the author

Karl is the physical embodiment of an alternate universe where Kurt Cobain played for Hanson, instead of Nirvana. When he’s not furiously bashing a keyboard and howling in pain, he can probably be found mumbling into a microphone somewhere, or up in the gym working on his fitness (with Fergie as his witness)

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