London - J Kenji López-Alt had little interest in cooking until he took a part-time job in a kitchen while studying at the Massachusetts Institute of Technology.
The son of a microbiologist, he is a self-confessed “science geek” who, until entering college, had only ever made guacamole.
But in spite of himself, he found he loved working with food. “For me, restaurants are exciting and fun and the whole idea of feeding people and making them happy was really appealing,” he says. “But at the same time, a restaurant is not a great place to practise science or experiment. I naturally had all these questions I wanted to ask. Why did we do things a certain way? So often the chefs couldn't explain; it was just a case of 'This is how it's done'.”
After going on to work as a chef and recipe developer for Cooks Illustrated magazine, he moved to San Francisco and decided to merge his love of food and science by starting the Food Lab, which explores the science behind cooking methods in classic American recipes.
Here, López-Alt offers some tips on a few favourites and shows us where we may be going wrong in the kitchen.
Slicing onions
The first tip is the same as slicing anything - get yourself a really nice sharp knife. Not only is it really difficult to cut with a dull knife but, with things like onions, you'll end up crushing cells instead of slicing through them and that's not good for flavour. Imagine the root end and stem end of an onion as two poles on a planet. If you cut the onion along the equator, you rupture a lot more cells leading to a less sweet taste.
The chemical compounds in an onion that make you cry are called lachrymators, which don't actually exist within the onion in its natural whole state. They're formed when you cut open onion cells and a couple of different precursor chemicals interact and form these pungent compounds. Using a dull knife or cutting across the equator will crush the cells leading to those chemicals being released. A sharp knife minimises this, resulting in fewer tears.
Poaching eggs
Your real enemy here is a loose white. If you crack open an egg you'll see it's not just the white and the yolk. You'll notice the white is divided into two separate parts: there's the white that's inside a membrane and the white that's loose and watery. It's the latter that's a problem as it is already separated and will cause havoc when poaching. As eggs get older the ratio of watery white to tight white goes up, so the fresher the better.
To keep the egg intact, crack it into a bowl, then tip it into a fine mesh strainer and swirl it around a little. You'll see the excess watery white drip through. From there you can gently roll it out of the strainer and into the simmering water. They should come out perfectly.
Salmon
Who hasn't had salmon that's fallen apart in the pan? First up, pre-heat the oil. Fish often sticks to a pan because a chemical bond forms between the fish and pan at a molecular level and, as fish tends to be tender, it easily tears. The key then is to make sure the skin heats up as fast as possible. Any kind of moisture on the salmon will quickly rob energy from the hot skillet, so press the fish first with paper towels before placing skin down. A lot of people think the temperature of the fish and meat going into a pan affects how well it sears but what really matters is the surface moisture: if there's any on it, until it's evaporated, the upper limit of the temperature of that meat is going to be 100C - the boiling point of water.
The skin shrinks when it cooks because of proteins tightening and water and fat being driven off, meaning it curls up on itself. To prevent this, hold a flexible metal spatula over the fillet for the first minute or two of cooking which should set the shape and prevent it from falling apart.
Chicken stock
Chicken stock can be as easy or as complicated as you want to make it. Some people are happy to let a stock simmer away for four hours but there is a quicker alternative.
You can put a whole chicken in a pot and it will extract flavour relatively slowly or you can chop it up a little so it will extract faster. Or you can chop it up a lot and extract flavour really fast. I recommend tossing the chicken carcass into a food processor and whizzing until it's relatively finely ground. Then simmer that with water and vegetables and it will extract flavour really, really fast. In 45 minutes you'll have the same amount of flavour as you would usually need a few hours for.
The only problem is that you won't get any gelatine in your stock, which is a function of temperature and time. Bringing stock to the boil won't extract gelatine. At a 100C simmer, it will take around four hours for the connective tissues to convert. There's no way to rush that. But if you add packet gelatine to the 45-minute stock it will add that body you want and will taste exactly the same.
Dried pasta
It is often said that if you start with a large volume of water the temperature drops less when you add the dried pasta and therefore returns to the boil faster. This is not true. It will either return to boil at about the same time or, in most cases, a small pot will return to the boil faster. The reason is that although the small pot drops in temperature more, it also has a smaller volume so it requires less energy to recover.
It is also often said that you need a larger vessel so that the pasta can move around and not stick. Pasta sticks to itself when starch and protein are still in a raw state. So as long as you stir a little during the first minute or two of cooking, you can pretty much leave it alone after.
Steak
Salting steaks is a contentious issue. Some say to put it on after it's cooked, others right before, others well in advance. What I found is that this goes back to the idea that moisture is the enemy of proper browning.
When you salt a steak, initially it draws out some of the liquid from the meat so you'll start seeing liquid beading up on the surface, and if you put your steak in a skillet or on a barbecue five to 45 minutes after salting that surface, moisture causes a lot of problems. It causes the temperature of the grill to very rapidly drop and it doesn't end up browning properly.
If you want to be quick, then salt the steak before immediately putting it on the grill. But if you have a little bit of time your best bet is to salt the steak and let it sit on a rack for a minimum of 45 minutes. Eventually, the salt forms a brine that breaks down a meat protein called niacin. This loosens the muscle structure allowing it to reabsorb that brine, so that the liquid returns to the meat along with some of the salt. The exterior surface ends up really dehydrated - which might seem bad, but you end up with a juicier steak overall because it browns much more efficiently and spends less time in the skillet.
The Food Lab: Better Home Cooking Through Science by J Kenji López-Alt (Norton) is out now
The Independent