In large part, that's because we have evolved to respond to two important signals when encountering food. The first is a "nutrition" signal that tells us the food will deliver a hefty dose of easily digestible calories, vitamins, and minerals. The second is a "general harmlessness" signal that tells us the food won't kill us.
The Maillard reaction is evolution's way of combining these two signals into one super-signal, specific to the roasty or browned flavors of cooked food. 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.
Long story short: 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.
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. That steak doesn't just need heat, though—it needs a relatively high level of it if you want surface browning to kick in.
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. 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. 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. The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, usually requiring the addition of heat. Like caramelization, it is a form of non-enzymatic browning. The reactive carbonyl group of the sugar interacts with the nucleophilic amino group of the amino acid, and interesting but poorly characterized odour and flavour molecules result.
This process accelerates in an alkaline environment because the amino groups do not neutralize. This reaction is the basis of the flavouring industry, since the type of amino acid determines the resulting flavour. In the process, hundreds of different flavour compounds are created. These compounds in turn break down to form yet more new flavour compounds, and so on.
Each type of food has a very distinctive set of flavour compounds that are formed during the Maillard reaction. It is these same compounds that flavour scientists have used over the years to create artificial flavours. Non-enzymatic browning -- the result of the Maillard reaction and Caramelization of carrots.
Caramelization is a form of pyrolysis , which is a generic term to denote any irreversible chemical decomposition driven by heat, more specifically in the absence of oxygen. Pyrolysis occurs outside of culinary endeavors. For example, when wood is converted into charcoal orwhen buried organic matter turns into a fossil.
If the sugars are heated excessively pyrolsis is easier to distinguish from caramelization. Sugar that has undergone extensive pyrolysis will be darker and much more bitter. For example, bread dough will transform from a delicious bun into an inedible black lump if left in the oven for too long. Maillard reactions are responsible for the good flavor of heat-browned, carbohydrate-and protein-containing foods such as grilled and roasted meats yes, there are sugars in meats , bread crusts, and onions.
Moreover, many recipes for caramelized onions prime the pump by including a teaspoonful of sugar. The moral of the story is that the word caramelization should be reserved for the browning of sugar, any kind of sugar, in the absence of protein.
When sugars or starches occur together with proteins, as they do in onions, breads, and meats, the browning is mostly due to Monsieur Maillard, not to caramelization.
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