The Science of Cooking
Food is often advertised as being “chemical free” but of course that’s not really true – all food is literally made from chemicals. Even the most pesticide-free, organic tomato ever grown contains millions of molecules of Lycopene, an unsaturated hydrocarbon carotenoid (chemical formula C40 H56) that makes tomatoes red, grapefruits pink, and apricots orange. That means cooking is applied chemistry, and every time you cook, you’re arguably a chemist! Your new book, The Science of Cooking, is all about how to understand the chemistry of food, and how that’ll help you become a better cook. So what chemical reactions are occurring when we “cook foods with acid (yay, ceviche!), grill meat, and steam veggies? Take a look at the incredible chemical reactions of everyday dinner.
The Science of Cooking has a great section, above, on how to cook meat. Maybe the most important chemical reactions when you’re preparing meat is the conversion of collagen to gelatin; this is what makes tougher cuts turn into nice, tender ones. This conversion happens at temperatures above 50 °C (122 °F), and it happens more quickly the higher the temperature. But since hotter temps also squeeze more juice out of muscle fibers and accelerate the unraveling of proteins that affect taste and texture, the best tradeoff is to cook at a relatively low temperature (say, 60 °C/140 °F), for a longer period of time; that‘s the principle behind braising, slow-cooking, and sous-vide techniques.
Here’s another meaty chemical reaction you might find interesting: did you ever wonder why fast food restaurants advertise their burgers as “1/4 pound before cooking”? Burger meat is generally about 72% water, and 30% or more fat; a lot of the original patty is lost as oil liquefies and drips off, and water in the muscle fibers evaporates due to the heat (the water is also part of the reaction that turns collagen into gelatin). How much? There’s a 35% reduction in weight during the cooking process: the burger you end up eating is actually less than 1/5 of a pound!
The book also has a great section on preparing vegetables, with illustrations like the one on steaming. Cooking meat is about transforming proteins and fats, because the edible parts of animals are made of muscle protein that converts chemical energy into physical energy (motion); on the other hand, plants are stationary chemical factories for carbohydrate synthesis and storage, to create and expand their physical structure. Steaming is actually the fastest method for putting heat energy into food, because of the large amount of energy released by water vapor when it condenses onto whatever you’re cooking; but that efficiency drops immensely once the surface temperature of the food rises above the boiling point of water.
The book notes that 14% of the vitamin C in a veggie can be lost in steaming, and 54% by boiling them. So why do either? While cooking destroys some of the vitamins and nutrients in food, it also chemically alters them so they can be more readily absorbed by your body; so while the absolute amounts are lower, they may be more effectively used. If you want to lower the amount of vitamin loss when boiling a veggie, put some salt (about 2 tablespoons for every liter) in the water; it will make the veggies soften faster, and minimize the loss of cell contents into the water.
And finally – ceviche!!! “Cooking” with acid is a real thing: as the book mentions, the acid causes denaturing (unraveling) of the proteins in the fish, which then coagulate, re-forming with a different structure; it’s essentially the same process as cooking with heat, but it’s more delicate than thermal cooking and doesn’t change any of the subtle flavors the way high temperatures do. Acid also has a side benefit of making the dish smell less “fishy” by oxidizing and breaking down compounds that cause it including amines, adelhydes, and geosmin; and this goes for all fish you’re cooking, so feel free to spritz some lemon juice onto that salmon before you cook it.