The Chemistry of Food & Taste | Dr. Harold McGee

The conversation opens with Huberman saying that McGee's work has changed how he thinks about the metals used to prepare food. He says these interactions affect the experience of food and taste "not just small ways, but really profound ways." He asks McGee for one food-chemistry fact he finds especially interesting.

McGee answers with a story from writing his book on the chemistry of cooking. He says that at the time he "didn't know that much about cooking or about chemistry" and was learning as he went. When he was writing about eggs, he read that cooks recommended a copper bowl for whipping egg whites into the foam used in meringues and souffles. He describes that foam as a liquid that, with air bubbles trapped in it, comes to act like a solid. He searched the literature on egg chemistry, which he says was fairly extensive, but found no explanation for the copper advice. He concluded it was "probably an old cook's tale."

What changed his mind was an accident. While looking for cheap illustrations, he found an old engraving of an 18th-century French kitchen. It showed a boy whipping something in a bowl that resembled a modern copper bowl, and the accompanying key read "Whipping eggs in a copper bowl to make pastries." He reasoned that if the French had been doing this for hundreds of years, it deserved a test. He calls that reasoning a key lesson:

Test everything.

He then bought a copper bowl, despite the cost, and whipped egg whites in it alongside another bowl. He reports that "the difference was tremendous": the copper-bowl foam differed in color, texture and consistency in the mouth. He calls the discovery that a supposed cook's tale could hold "a kernel of scientific chemical truth" mind-blowing and career-changing, because from then on he took nothing for granted. In the excerpt, the evidence is his own informal comparison. He does not explain the mechanism.

Huberman says he recently started drinking from a copper water bottle and likes the taste. He adds that he has not checked whether the health claims made for copper are true or nonsense. He asks whether copper is used to bring out the best flavor in other foods.

McGee names jelly and jam-making. Preserves are cooked above the boiling point, and he says that in a pan of any other material the high heat disturbs almost everything in the mix, the sugars in particular. When sucrose breaks down into glucose and fructose, the behavior of the material "changes a lot, and it's not necessarily for the better." He says copper inhibits that breakdown, which is why cooks, and French cooks in particular, have made preserves in copper for generations.

Huberman calls this an "unconscious genius combined with experimentation." McGee's answer is a caution against scientific overconfidence. He says that when scientists became interested in cooking, they sometimes proposed changes that "were terrible ideas," and the traditional methods were in fact much better. In his account, the scientists acted on a partial understanding and set out to correct cooks they assumed were less intelligent. His example is mid-19th-century cookbooks published in England and the US with subtitles such as "In which the theories of Dr. Liebig have been as much as possible applied in the recipes." He calls Liebig "a genius biochemist" who, on cooking, "kind of took his genius for granted and was wrong." His verdict:

The cooks knew better.

Huberman applies the same tension to current health and nutrition. He describes papers that identify mechanisms which then do not play out in clinical trials. He also describes people doing things for which "there's really no peer-reviewed research," who still give the sense they may be onto something. He calls this an intersection, "or sometimes the collision," of expertise and real-world results. This is a general observation, and he does not give specific studies.

Moving on to heat, Huberman first answers a question he often gets. He says microwaves are safe, though you "probably don't want to stand right in front of it" in case the mesh protector is less effective than it should be. He then asks how heat, which he imagines started with fire, interacts with food chemically so that people enjoy it more.

McGee notes that the anthropological literature focuses on practical gains from cooking: more calories, and the ability to eat things we could not otherwise eat as efficiently. He believes fire would not have caught on unless it also made food more delicious. He suggests that early people probably learned to link particular sensory experiences with a food's nutritional value, "and maybe even the safety." His example is the leftovers from killing a mammoth, which had to be kept from spoiling and making people sick. He presents this as his own view, not as an established finding.

His central point is about molecular size. Proteins, carbohydrates and fats make up food, but they are macromolecules, "way too big for us to experience directly." Heat rearranges these materials and breaks enough of them down into small molecules that our senses of taste and smell can detect. He adds a broader claim about why we enjoy this:

My feeling is that we have our senses for them to be stimulated.

He says that even when the stimulation is only borderline pleasant, or slightly unpleasant, we still enjoy it. In his telling, cooking turns molecules with no taste or smell into "bouquets of various kinds," depending on what the food started as.

Huberman makes this concrete with steak. Raw, it is unappetizing to him and bland. A seared, medium-rare steak, particularly one with the charred exterior and rare interior he calls a "Pittsburgh char," is delicious. He asks why cooking makes meat taste of more, not just of something different.

McGee explains that meat is mostly protein and fat. Heat is energy, and it agitates molecules at the surface of the food enough to break them into much smaller pieces. Those pieces are also reactive: they react with each other and with oxygen in the surrounding air. As transcribed, his comparison of the aroma of steak tartare with that of a Pittsburgh char is muddled. It says first that even instruments would find "very little noticeable difference" and then that the cooked steak gives off "a tremendous amount of volatile molecules," the ones our noses detect. The point he seems to be making is that cooking produces both aroma volatiles and small molecules that stimulate taste receptors for sweet, sour, salt, bitter and umami, "even though they are not sugars or salts or whatever."

What I like to think of is just the alchemy of heat. You take this material, you add energy, and you transform it in ways that are delightful to us.

Huberman checks his understanding: cooked steak can stimulate sweet receptors because heat shrinks the meat's molecules and changes their configuration. McGee agrees and adds a point about scale. Molecule counting has become so good, he says, that "who knows exactly how many" molecules a raw piece of meat contains. Whatever the number, heat multiplies it many times by breaking materials apart and making them react, producing "an explosion of sensory information that simply wasn't there before."

Huberman raises umami, which he links, "at least in part," to savoriness. He describes the browned residue left by meat in a cast-iron pan as one of the most delicious things he knows. He also notes a puzzle: the same crumbs eaten two hours later taste awful, "like you were licking the grill of a barbecue from two days before." The excerpt does not go on to explain this difference.