What you need
Onions
A frying pan
Sodium bicarbonate
WELCOME to this new series on the science of cooking. In the coming weeks, I will shed light on the amazing transformations that turn simple ingredients into delicacies, and explain how you can use science to make your food taste even better.
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Let鈥檚 start where so many recipes begin, with frying onions. A typical recipe will ask you to cook onions until they are soft and brown, often claiming that it takes about 10 minutes. If you have ever tried it, you will know this isn鈥檛 true. Not by a long shot. It takes around 40 minutes to get properly dark, sweet-tasting onions.
But with a little knowledge of what is happening in the pan, you can halve this time and still get great-tasting onions.
The first thing that happens when onions cook is that the water inside the cells vaporises. The cells then burst, releasing sugars, proteins and a variety of aromatic compounds that make your kitchen smell great.
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Heat breaks down larger sugar molecules into smaller ones such as glucose and fructose, increasing the sweetness. These sugars fragment and recombine into hundreds of new molecules, creating sweet, sour and bitter tastes, in a process called caramelisation.
The proteins break down into their constituent amino acids, and it is when these react with sugars that the really delicious flavours start to emerge in what are called Maillard reactions. These produce a huge range of compounds and are behind the appetising colour and complex taste of many foods, including seared steak, dark beer and crusty bread.
All this takes time, gentle heat and stirring: if the pan is too hot or you leave some onions in contact with the surface of the pan for too long, they will produce bitter-tasting compounds before the centres have softened.
There are two ways to speed up the process. First, add alkali. Maillard reactions go faster in higher pH conditions. A dash of sodium bicarbonate (baking soda) will make onions brown much more quickly. It also weakens the pectin in their cell walls, so more cells rupture and release their contents. Don鈥檛 overdo the bicarb or you will get mushy onions with an unpleasant soapy taste 鈥� a quarter of a teaspoon will do for two or three onions.
Second, adding water allows you to raise the heat without burning. Water also dissolves any brown compounds stuck to the pan and spreads them evenly through the onions. You could also use wine or stock if you prefer.
With these cheats, you can get soft, rich, dark brown onions in about 20 minutes. Mix them with cr猫me fraiche to make an irresistible caramelised onion dip or use them as a base for onion gravy or soup.
Next week, I will show you how to harness ancient biotechnology to make cheese.
For next week
Milk
A thermometer
Rennet
A skimmer or slotted spoon
Cheesecloth
Next in the series
1 Caramelising onions
2 Making cheese
Harness ancient biotechnology
3 The science of crispiness
4 Tofu and Sichuan pepper
5 Gravlax and curing
6 Tempering chocolate
7 Umami and flavour
8 Perfect pancakes
9 Kimchi and fermentation
10 Sourdough bread
Science of cooking online
Projects will be posted each week at
Email: cooking@newscientist.com
