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The Maillard Science of Browning, Aroma, and Flavor

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An Introduction to the Maillard Reaction

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If you’re a regular reader of Serious Eats, you’ve definitely seen us refer to the Maillard reaction time and again. That’s because the Maillard reaction is responsible for the browned, complex flavors that make bread taste toasty and malty, burgers taste charred, and coffee taste dark and robust. If you plan on cooking tonight, chances are you’ll be using the Maillard reaction to transform your raw ingredients into a better sensory experience.

it’s the difference between being a slave to a recipe and being free to make a recipe work for you

But the Maillard reaction (The Maillard reaction (/maɪˈjɑːr/ my-YAR; French pronunciation: ​[majaʁ]) is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor).
doesn’t just make food taste delicious. Understanding the reaction, even on a surface level (that’s a Maillard pun, and you’ll totally get it soon), is a gateway to understanding the chemical and physical processes of cooking. Grasping the variables involved and learning how to manipulate them is one of the best ways to become a more confident cook—it’s the difference between being a slave to a recipe and being free to make a recipe work for you.

SO, WHAT IS THE MAILLARD REACTION?

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The Maillard reaction:is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, pan-fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and many other foods, undergo this reaction. It is named after French chemist Louis-Camille Maillard, who first described it in 1912 while attempting to reproduce biological protein synthesis.

The reaction is a form of non-enzymatic browning which typically proceeds rapidly from around 140 to 165 °C (280 to 330 °F). At higher temperatures, caramelization and subsequently pyrolysis become more pronounced.

The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid, and forms a complex mixture of poorly characterized molecules responsible for a range of aromas and flavors. This process is accelerated in an alkaline environment (e.g., lye applied to darken pretzels; see Lye roll), as the amino groups (RNH3+) are deprotonated and, hence, have an increased nucleophilicity. The type of the amino acid determines the resulting flavor. This reaction is the basis for many of the flavoring industry’s recipes. At high temperatures, a potential carcinogen called acrylamide can be formed.

In the process, hundreds of different flavor compounds are created. These compounds, in turn, break down to form yet more new flavor compounds, and so on. Each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. It is these same compounds that flavor scientists have used over the years to make artificial flavors.

All that cooking we’ve come to seek out is, at its heart, the process of applying heat to food over a period of time. If all goes well, it also makes you hungry. A burger, to extend our example, is composed of a basic set of building blocks: proteins, sugars, and water. The Maillard reaction is what can happen to those proteins and sugars when heat and time are added to the equation. With the right amount of heat, moisture, and time, those specific sugars and proteins will act like a couple of lust-drunk lovers making out in the back of a Chevy, rapidly becoming a tangled, hot mess, until, nine months later, a whole new creation emerges.

Except that with the proteins and sugars, it takes minutes, not months, and instead of a child, the result is an increasingly complex array of flavor and aroma molecules, along with a darker color courtesy of newly formed edible pigment molecules called melanoidins.(Melanoidins are brown, high molecular weight heterogeneous polymers that are formed when sugars and amino acids combine (through the Maillard reaction) at high temperatures and low water activity).

HEAT, MOISTURE, AND TIME

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The first thing you need for the Maillard reaction to take place is heat. A steak left to sit on the counter for a week at room temperature will certainly undergo some chemical changes, but the Maillard won’t be one of them.

The Maillard reaction occurs noticeably above 266 °F / 130 °C and quickens up to about 356 °F / 180 °C. Above about 356 °F / 180 °C, pyrolysis or burning creates charred, bitter flavors. Below 266 °F / 130 °C, the reaction slows to a crawl; what happens in minutes at 302 °F / 150 °C takes hours at 248 °F / 120 °C or weeks at 140 °F / 60 °C.

That steak doesn’t just need heat, though—it needs a relatively high level of it if you want surface browning to kick in. Boiling water, which tops out at 212°F (100°C) at sea level, isn’t hot enough. That’s why a boiled steak turns gray instead of dark brown, exciting the palate of exactly no one.

The Maillard can work at lower temperatures, and with a lot more water. If you cook a chicken or beef or vegetable stock at a bare simmer for eight or 12 hours, the result is still a brown, fragrant liquid—a dead giveaway that the Maillard has occurred.

But most of us aren’t cooking stocks for that many hours, and none of us are boiling a steak for anywhere close to that period of time. Instead, we’re roasting, frying, and grilling. These cooking processes happen relatively fast, in minutes rather than hours, and for the Maillard to happen quickly, we need to drive off enough moisture to break free of that 212° cap.

By cooking a steak in a ripping-hot skillet, you can dehydrate its surface thoroughly enough that the temperatures on that surface will begin to climb, to upwards of 300°F (149°C). At that point, the Maillard reaction will kick into full gear, creating new flavors, aromas, and the characteristic brown colors that give the reaction its more commonplace name, the “browning reaction.”

This is why it can be a smart move to pat your meat dry with towels or let it dry in the fridge for several hours before you cook it. It’s also why you should salt your meat either more than 45 minutes in advance of cooking (allowing enough time for the salt to draw out moisture through osmosis from the meat, which then reabsorbs that salty brine, turning the meat more tender and moist) or immediately before (allowing you to avoid significant moisture loss through osmosis altogether).

Ideally, you’ll have enough time to combine the two using a technique called dry-brining: salting the meat generously, then letting it air-dry in the fridge at least overnight and up to a few days before cooking. You’ll end up with meat that’s deeply seasoned while also sporting a nicely dried surface, perfectly primed for maximum Maillard once roasted or seared.

PROTEINS AND SUGARS

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Heat, moisture, and time may be key to getting the Maillard reaction going, but without proteins and sugars to work with, it simply won’t happen. Proteins are long chains of amino acids, crumpled up like wads of paper. Some of them are Maillard-susceptible, meaning they really love to bond with sugars. But not just any sugar will do. Molecules of complex sugars, like starches or table sugars, are too big to react with Maillard proteins. Instead, these proteins require “reducing sugars,” which are essentially simple sugars that attract amino acids at certain moisture and temperature levels.

That’s a critical point: The Maillard reaction starts with a somewhat limited set of proteins and sugar molecules, and, as these bond and mix over time, more and more new molecules are added to the equation. It’s kind of an incestuous molecular orgy, when you stop to think about it. (Gross! And also…yum!) These promiscuous molecules mix and match over and over, billions and trillions of times per second, on the surface of a food, forming a growing, recursive, recombinatory aroma and flavor engine.

This engine is influenced by temperature, time, and pH—all things that home cooks can control. If you want to make lots of flavor and aroma compounds, just raise the pH a little with baking soda (as Kenji does to make quick-caramelized onions for his Pressure Cooker French Onion Soup). Looking for a crisp, browned crust? Just lower the pH with a little acid, or increase the temperature. Want a little of both? Frying in fats gives you the best of both worlds.

BUT…WHY DO WE LIKE IT?

Marinades are usually made up of three components: acid, oil, and herbs. The acid helps to partially denature the meat’s proteins, opening up “tunnels” in the meat structure where flavor can seep in. But marinades mostly penetrate only the surface. Marinades work best on meats such as chicken breast and fish, because the muscle structure is not as dense as it is in steak. For denser meat, marinades work best when the meat is cut into smaller pieces so the marinade can penetrate a larger surface area. However, if marinades are left on too long, the acids can “cook” the surface, causing the meat to dry out. Some meats, such as pork and steak, can marinate for hours. Other less dense cuts of meat, such as chicken breast and most fish, only need to stay in a marinade for a short time.

Brining meat (that is, putting meat into a salt-water solution) adds moisture to the meat through osmosis. Osmosis happens when water flows from a lower concentration of a solution to a higher concentration through a semipermeable membrane. In meat, this membrane is the plasma membrane that surrounds the individual cells. When meat is placed in a brine, the meat’s cell fluids are less concentrated than the salt water in the brining solution. Water flows out of the cells in the meat and salt flows in. The salt then dissolves some of the fiber proteins, and the meat’s cell fluids become more concentrated, thus drawing water back in. Brining adds salt and water to the cells so that when the meat is cooked and water is squeezed out, there is still water left in the cells because water was added before cooking.

FAT MATTERS

Fat, an energy source stored in animal muscles, also contributes to the flavor of meat. Water is the most prevalent component of meat, and most of the flavor-carrying, or aroma, molecules are hydrophobic (repelled by water). These molecules dissolve in fat.

Meat’s fat content varies from animal to animal, and within each animal, it varies from part to part. Muscles that are used often consume the stored-up fat, and so the meat from these areas don’t have much fat. Areas that aren’t used as much don’t use as much energy, so there is more fat in these cuts. The animal’s age also plays a role in how much fat is in the meat. The older the animal, the more time it has had to build up fat-pocket energy reserves in its muscles.

BEEF:Cattle that are bred for consumption are often fed large amounts of food in order to increase the amount of fat that normally occurs. The more fat in a piece of beef, the more “marbled” its appearance; that is, the more white streaks of fat there are. Marbled steaks are considered to be some of the most flavorful beef cuts.

PORK:As a result of the health risks that may be associated with consuming too much red meat, pork is now a popular alternative to beef. Pigs that are slaughtered are, for the most part, fairly young, and their muscles haven’t built up energy reserves. There are some pork cuts that are naturally fatty, such as bacon, but breeders are now using techniques to produce leaner pork. The result is that many pork cuts now have about the same amount of fat as the white meat in chicken.

FISH:With fish, it’s a different story. The fat in fish comes from the oils distributed throughout their flesh; it isn’t stored in pockets as it is in beef and pork. These oils have subtle flavors in and of themselves, and they contribute to the flavor of the fish.

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