Scientific baking – your guide to chemical reactions in cooking

September 23rd, 2015

Appliance Talk Ovens Ovens & Cooking

Have you ever baked a cake, or a tray of biscuits in your oven?

If you have, then I have news for you: YOU’RE A SCIENTIST.

It may not be as dramatic as a large bearded man telling you that you’re a wizard, but it’s the truth.

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By following a recipe to bake a tasty treat, you’re effectively confirming a set of scientific principles by reproducing a specific series of chemical reactions. In this case, changing the composition of your ingredients from raw dough to cooked cakes, breads or biscuits.

And if you reckon making a few alterations to your recipe may make the end results taste better, and you put your ideas into action, that’s making a hypothesis and performing an experiment – the bread and butter of science (literally!).

With that in mind, here’s our basic guide to some of the broad chemical reactions that take place during baking, and how you can play with them to get different results, all using baking a tray of biscuits as an example:

Melting butter

Butter is not only tasty, but an emulsion – a combination of water, fat, and dairy solids that wouldn’t typically stay together under natural circumstances.

When your oven reaches approx. 33°C, the butter begins to melt and its elements begin to separate. The fat spreads out, causing the dough to fill the pan or tray. The water heats and turns to steam, causing the dough to expand outwards as it tries to escape.

With this in mind, adding some extra butter to a recipe may give you bigger, fatter biscuits. Or it could just leave eveything extra-slippery…

Killing germs

Humans aren’t the only household creatures that enjoy feasting on fresh food – germs do too.

source: NIAID on Wikimedia Commons

Germs tend to thrive in temperatures between 5°C and 60°C. As soon as the perishable ingredients in your baking (such as eggs) come out of the fridge, they’re enter this temperature danger zone, causing any germs to start multiplying like crazy.

It’s not until the dough is in the oven and reaches the 60°C mark that you can be confident that your baking is germ-free.

Changing proteins

As we discussed the other day, eggs (a key ingredient in a fair few baking recipes) are mostly made up of tangled proteins.

Sunbeam Egg Cooker EC1300

Heating these proteins to around 60°C causes the strings to start untangling and linking with one another into a more solid mass.

So if you add more eggs to your baking, in theory you’d end up with a harder, or at least denser result than using fewer eggs.

Boiling and evaporating water

Boiling water is one of the most fundamental chemical reactions. At 100°C, water boils and starts to evaporate from a liquid into a gaseous state.

source: Markus Schweiss on Wikimedia Commons

In baking, when your oven reaches this temperature, your dough will dry out as the water that separated from the butter earlier turns to steam, leaving air pockets behind for a lighter, fluffier texture.

The air pockets left behind by the evaporated water help give your baking a softer texture. Another way to achieve this results is to leaven your dough. Let’s look into that…

Leavening

Also known as “raising”, this is the process of further adding additional gas bubbles to dough so it turns out lighter and softer. This requires the addition of an extra leavening agent to the dough.

source: ElinorD on Wikimedia Commons

When baking bread, yeast is used as a living leavening agent to get the dough to rise before the baking process begins.

source: Jonathunder on Wikimedia Commons

But for something like biscuits, where a longer fermentation process isn’t required, one of the most common chemical leavening agents is sodium bicarbonate, also known as baking soda or bicarb soda.

Bicarb soda is what is scientifically known as a “base” and reacts with acids in your baking (usually from dairy) to produce carbon dioxide gas. Much like the water and steam mentioned earlier, this gas leaves bubbles in your dough, resulting in a lighter, fluffier texture.

While it may sound like a good idea to add extra baking soda to get an even fluffier texture in your baking, we’d recommend being conservative in your experiments. If there aren’t enough acidic ingredients in your recipe, the excess bicarb soda will be left over in your dough at the end, and it’s not a great flavour!

The Maillard Reaction aka browning

Everyone knows that food turns brown as it cooks… but WHY exactly does this happen?

The answer comes courtesy of French biochemist Louis Camille Maillard (pronounced “my-yar”), who in 1912 undertook a study of the reactions between  amino acids and sugars in food at elevated temperatures. This reaction not only changes the colour of food, it also affects its texture and flavour.

The exact chemical process of the Maillard reaction is a bit complicated to be looked at in detail here (for more info, check out this article about John Hodge’s 1953 research into the reaction’s mechanisms), but the most relevant aspects for bakers to know are:

• The reaction begins to occur when your food reaches 140°C
• It continues right up to 165°C
• It makes your food look and taste better!

Once this reaction takes place, it’s on to the next step, which is…

Caramelisation

This is the name of the process that makes browned food go from being not just tasty, but sweet as well, as the maltose carbohydrate molecules in the dough start to break down and rearrange themselves under heat.

Source: Nicola on Flickr

It’s a separate chemical reaction to the Maillard reaction, and takes place afterwards, starting when the food reaches 180°C, and continuing through to 200°C.

If your food gets much hotter than this, there’s a risk that after the Maillard and caramelisation reactions, you’ll end up also experiencing the pyrolysis reaction, also known as burning. Unlike a self-cleaning pyrolytic oven, this will NOT leave your appliance nice and fresh!

Conclusion:

Here’s a brief summary of the chemical reactions that take place when baking a tray of biscuits:

• 33°C – butter melts, spreading out the dough and leaving water pockets
• 60°C – germs are killed off, egg proteins solidify the mixture
• 100°C – water evaporates, leaving air pockets in your mixture, along with those of the bicarb soda
• 140°C-160°C – the Maillard reaction takes place, browning your biscuits
• 180°C-200°C – caramelisation occurs, sweetening your baking

Here’s a short video summing up these chemical reactions. It is an American production, so be prepared to mentally translate “cookies” to “biscuits” and the various Fahrenheit measurements to Celsius, but otherwise it sums everything up pretty solidly:

And if you’re in the mood to experiment when baking in the kitchen, let us know how you go! As Mythbuster Adam Savage puts it, “the only difference between screwing around and science is writing it down.”