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Common Kitchen Chemistry Explained

Although we rarely think about it, most of us participate in chemistry experiments on a daily basis. Whether you’re cooking for yourself or having someone else do it for you, turning raw ingredients into finished meals requires sometimes simple and oftentimes complex chemical reactions. In culinary circles, these processes are hotly debated and highly deconstructed. In most kitchens, however, most of us stumble through on dumb luck, common sense, and dense recipe books.  

Perhaps that’s why so many myths and mysteries still abound. But learning what makes our food turn from liquid to solid, from raw to cooked, could just make our cooking a successful experiment.

Tomatoes Don’t Like the Chill
Although we’re used to mealy tomatoes in the winter, how we store them can also contribute to their unsatisfying texture. Since they’re used as a vegetable, many people think they should be placed in the crisper drawer in the refrigerator. However, the cold damages the cellular membranes and causes the funky texture as well as flavor loss. Best place to store ’em? Anywhere at room temperature. Like other fruits, tomatoes will continue to ripen and mature after picking. 

High Heat Seals in Juices, Right?
It’s common kitchen teaching that you’re supposed to cook a piece of meat at high temperature to “seal” in the juices. However, this is incorrect. The high heat actually pushes the water out of the muscle fibers, which is why you hear a sizzle when cooking a pork chop or other meats.

However, you’ll also probably smell the delicious scent of cooking meat. That’s from a process known as the Maillard reaction, which happens when surface amino acids (the building blocks of proteins) and sugars react at high heat. This results in a “meaty” flavor and a browning of the outside. It also produces new flavor molecules, which are strongest on the surface and a good reason to keep that heat high.

The Maillard reaction doesn’t just occur when cooking meat, however. Any time amino acids, sugar, and high temperatures are present it can occur. The smell of baking bread, the color of beer, and the flavor of toast are all due to the Maillard.

Mixing Oil and Water: Add an Egg
We all know that oil and water (or vinegar) don’t mix. But everything from hollandaise sauces to bottled salad dressings manage to make them mingle, and often times it’s because of an emulsifier, such as an egg.

Egg yolk works as an emulsifier because it contains some compounds that like water and some that don’t. The proteins in the yolk will essentially hold onto both the fat molecules in the oil and the water molecules in the vinegar, creating a link between them and preventing them from separating or preventing them from clumping back together.

Soaps work much in the same way. They have phospholipids, which are chemicals that have a polar (water-loving) head and nonpolar (water-hating) tail. The nonpolar tail binds with grease and dirt on your hands, while the polar head allows it all to be swept away with water. 

Keeping Grey out of the Green
It’s common for green vegetables, such as broccoli, to turn a bright, cheery green after a minute or two in hot water, only to fade to grey upon further cooking. But according to Harold McGee’s book, On Food and Cooking: The Science and Lore of the Kitchen, there is a way to prevent this.

First off, the broccoli doesn’t actually turn more green, it’s just that the heat causes an expansion of the cellular structure which allows gases to escape. This allows us to see more clearly the green color of the chlorophyll. When cooked longer, however, two things happen: color becomes water soluble and leaks into the surrounding environs and a magnesium molecule in the center of the chlorophyll molecule is displaced, causing a change in the color structure. This happens most often in acidic water, so a simple way to prevent it from occurring is to add a small amount of baking soda to the water. Since many municipalities already keep their water slightly alkaline, you might not experience the problem at all. McGee also recommends cooking for shorter temperatures and waiting until the last minute to dress cooked greens with an acidic dressing.

Taking the Bite out of It
One thing I’ve noticed with particularly spicy greens (like farmer’s market arugula) is that they seem to lose a bit of their punch once dressed. This is because of the basic rule that most cooks know when they add something sweet to make a dish less salty—adding one taste can alter the sensation of the other. Therefore, pouring on a salty dressing can curb the bitter flavor of a green.

Since our sweet, salty, sour, and bitter tastes all interact for the eating sensation, altering one necessarily affects another. One creative way to take the bitterness out of tonic water (unless you like it, as I do), for instance, is to add a pinch of salt. It’s also why many people add sweeteners to otherwise bitter coffee or why bitter India Pales Ales are mellowed out with malt.

What to Put in Pasta Water
Pasta might be one of the simplest things to cook (boil water, add noodles) but perhaps because of it’s austere yet ubiquitous preparations, there is much debate. Should you add oil to the water? What about salt? Factions and dissenters abound.

The consensus seems to err on the side of no oil, yes salt. Although in theory oil will prevent your pasta from sticking, in reality it rests on the top of the water and much of it is poured down the drain. It also can prevent sauce from sticking to your noodles.

As for salt, it raises the boiling point of water, theoretically making the pasta boil faster (in reality, the amount we add barely does anything.) The main reason it’s nice to add it to pasta water is that it imparts flavor to the final product.

These few steps are just the tip of the iceberg; there’s as much to know about ingredient chemistry as there is to know about how to combine them. Luckily, eating it is easy.