Cooking may have been our first great leap forward as humans. Besides killing off harmful bacteria, cooking our food made nutrients become more easily absorbed, which allowed our brains—our number one consumer of energy—to considerably increase in size. Besides the safety and nutritional aspects, cooking has one more major advantage: It makes food taste much better. Most foods, particularly meat, undergo a series of chemical reactions when exposed to certain temperature ranges, resulting in the synthesis of endless compounds that make life taste sweeter.
Even those who aren't self-described foodies have probably heard of the Maillard. The key process across global cuisines, the Maillard reaction happens when we cook meat, bake bread, and make French fries. Even maple syrup owes its amber color and some of its flavors to the Maillard reaction. Pretty much every time proteins and carbohydrates are heated up together they undergo this reaction which results in delicious flavor and mouthwatering coloration.
The Maillard reaction itself is actually pretty straightforward. It simply involves adding a sugar to the end of a protein chain via their carbonyl and amino groups, respectively. The resulting carbohydrate-protein hybrid then rearranges and breaks apart to form a myriad of small molecules that turn meats brown and give them great flavor.
While the Maillard reaction is definitely the most well known and, arguably, most important reaction during the cooking process, the Strecker reaction is not that far behind. In the Strecker reaction one of the Maillard products goes one step further by combining with the amino acid methionine to make yet another volatile flavor compound.
During the Strecker reaction an α-dicarbonyl compound, which was produced during the Maillard reaction, reacts with methionine, which is an amino acid commonly found in cells. Once the bond between the two is made, one molecule of each water, carbon dioxide and ammonium are released, leaving behind only methional. Methional is one of the main odor components in cooked meat, so if you like how your turkey smells while it’s sizzling, you are a fan of the Strecker reaction.
This chemical reaction is a bit of a double-edged sword. While lipid oxidation is a highly desirable reaction to occur during the cooking process, it also gives rise to the rather unpleasant rancidity associated with old meat. More than that, if allowed to go on long enough, this type of oxidation can compromise the texture of the meat and form toxins, which of course should be avoided at all costs. So we want lipid oxidation at the time of cooking, but not before or after, if you value your leftovers.
The reaction of lipid oxidation is a two step process. First, the fat in the food forms a radical which has an unpaired electron in the valence shell, making it highly reactive. The radicalization of the fat isn't understood very well, but currently its thought that iron is the main culprit in turning otherwise inert fat into a highly reactive agent.
Since radicals are highly reactive, they rarely last very long in any system and will react with pretty much anything. In this particular case, the radical actually reacts with itself, causing it to split the long chain of the fat in two. The resulting smaller molecules are alcohols and aldehydes, which can be quite pungent en masse, but give rise to pleasant flavors in small amounts.
Most people don’t associate vitamins with the “meat” food group, but some vitamins, like vitamin B6 and vitamin B1 (thiamine), are actually abundant in muscle tissue. Thiamine in particular is present in all kinds of different meat at relatively high concentrations, but doesn’t actually contribute anything to flavor by itself, as it is tasteless. Luckily for us, it is also rather unstable at high temperatures and breaks down into some other compounds that smell and taste delicious.
During cooking, thiamine is decomposed into sulfur containing compounds, which typically have very pungent aromas, as most organic chemists can tell you from experience. Just for reference, the chemical added to natural gas to give it that distinct smell is in the same chemical class of sulfur-containing molecules (mercaptans), so the fact that it is perceptible by humans should not be surprising. What is surprising is that we perceive these particular mercaptans as a pleasant meaty aroma, which contribute to the whole culinary experience.
All trussed up
There's quite a bit of chemistry going on unsupervised inside that oven while we watch the game and wait for the timer to go off. In order for this chemistry to progress perfectly and make the best turkey possible, the bird needs to be brought up to the right temperature kept there steadily and uniformly. That’s where your oven comes in. So, if you're into science like we are, and you want the best chemistry possible to happen in your kitchen, make sure you get an oven that's up to the task.
Contributing Author: Ethan Wolff-Mann