You're cooking onions wrong! Scientists reveal the secret to cooking the vegetable twice as fast - and all it takes is one unusual ingredient

Whether you're making a comforting stew or a mouthwatering curry, they are often the first ingredient you reach for.

But scientists say that you might have been cooking your onions wrong.

To get the truly deep, caramelised onions needed for many dishes, some recipes require upwards of 30 to 40 minutes of cooking.

But with a little scientific knowledge and one simple ingredient, you can more than half that time.

The secret comes down to controlling the speed of a chemical reaction known as the Maillard reaction, which is responsible for making food brown and delicious.

Since this reaction is dependent on pH, chefs can speed up or slow down the reaction as they need.

So in order to make onions brown faster, we need to increase their pH by adding something alkaline to the mix.

That's why just a pinch of baking soda is the key to unlocking delicious flavours in just a fraction of the time.

Why does baking soda make onions brown faster?

When you drop onions into a hot pan, a whole range of chemical and physical reactions start happening all at once.

First, the water inside the onion's cells boils and vaporises, tearing the cells apart and releasing a burst of sugars, proteins, and other volatile chemicals.

As the heat rises, that mixture of chemicals starts to react and combine in a complex set of processes we recognise as cooking.

However, when chefs talk about caramelising onions, this is actually a bit misleading.

Caramelising happens when the long chains of carbohydrates in starch and complex sugars break down into shorter molecules like glucose and fructose.

Those simple sugars then combine into hundreds of different molecules to create the bitter-sweet flavours we find in cooked or burned sugars.

But the kind of browning chefs are interested in is actually another set of extremely complex interactions.

While the sugars are breaking down into smaller pieces, heat from the pan is also breaking up complex proteins into amino acids - the basic building blocks of biology.

Professor Marianne Lund, a food chemist from the University of Copenhagen, told Daily Mail: 'This initiates a cascade of reactions called the Maillard reaction, which eventually leads to brown pigments, called melanoidins.'

In addition to making onions brown, this reaction also produces a host of volatile compounds which give roasted foods their distinct smell and taste.

This is the exact same reaction we find in the browning on a perfectly cooked steak or in the hearty crust on a loaf of bread.

Controlling how and when this reaction occurs is something that any cook does without realising, but we can get even more control using science.

Professor Lund says: 'The reactivity of the reactive sites on proteins is increased under alkaline conditions.'

That means the higher we make the pH, the faster the Maillard reaction will occur and the quicker onions will brown.

Since onions naturally have a slightly acidic pH of around five, adding something alkaline will drastically improve cooking speeds.

You don't want to add too much baking soda, but around an eighth to a quarter of a teaspoon for every three onions will yield dramatic results.

With the pH adjusted, you should be able to achieve levels of browning that would normally take half an hour in around 10 minutes.

You'll also need to make sure there are plenty of raw materials for the Maillard reaction to use, including both proteins and sugars.

That's why adding some dairy protein-rich butter not only makes your food taste great but also helps it cook faster.

Why you shouldn't always add baking soda to your onions

Although adding baking soda will reduce the cook time, there is an important caveat to remember.

That is because the Maillard reaction isn't the only chemical process that is affected by increasing the pH.

Alkaline conditions also weaken pectin, the natural starch which gives stability to the cell walls of plants.

That means adding baking soda will lead to your onions breaking down a lot faster than normal.

If you're not careful, this can result in a deeply browned onion paste, more like an onion jam than the solid strands of caramelised onions you might find in French onion soup.

It may be perfect if you want your onions to dissolve into a sauce or spread evenly through a dish, but not great if you want onions with some bite.

So, you will still need to think about whether the time-saving benefits are worthwhile for the dish you have in mind.