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The Maillard Reaction

The Maillard Reaction takes its name from Louis-Camille Maillard, the scientist who first studied this effect in the early 20th century. It’s the factor that makes toasted bread so tasty, roast potatoes so irresistible and a char-grilled steak so delicious. So if you’re planning on cooking up a storm this evening, it’s more than likely you’ll be relying on the Maillard Reaction to turn your essential ingredients into a culinary delight.

 

While we humans have been cooking food to make it tastier for millennia, scientists have only recently begun to unveil what the Maillard reaction involves. In essence, it’s the sum of many tiny chemical reactions happening simultaneously to transform the sugars and proteins in food to create new colours, aromas and flavours.

 

Types of produce with the Maillard reaction

The Maillard reaction is the reason for the flavour and colour of a wide range of foods:

  • Caramel made from sugar and milk
  • Toasted bread
  • The brown colour of beer, coffee, chocolate and maple syrup
  • The flavour of roasted meat
  • The colour of condensed and dried milk
  • The biscuity aroma of baked goods such as bread, popcorn and tortillas.

The Maillard reaction produces water, and water inhibits the reaction; this is why a flash-fried steak looks and tastes very different from boiled meat. For the Maillard reaction to occur, you need three things: heat, proteins and sugars.

 

Heat

For the Maillard reaction to occur, the first thing you require is heat. If you leave a piece of steak at room temperature for a week, it will have undergone some changes in its chemical structure. But it will not have undergone the Maillard reaction.

The heat level required for the Maillard reaction is relatively high. Water boils at 100°C, and this isn’t hot enough. This is why boiled meat looks grey rather than brown – not particularly appetising! It’s true that if you simmer a chicken in stock for a day or two, you eventually obtain a rich brown gravy. This is an example of the Maillard reaction. But few of us have that much time to spare, and even fewer want to boil our steaks!

Chefs prefer quicker methods such as grilling, frying and roasting, cooking methods that take no more than a couple of hours and often just a few minutes. For these faster methods, you need to drive off as much water from the food as possible to break through the 100°C temperature so that the Maillard reaction occurs quickly.

That’s why chefs pre-heat the skillet before cooking a steak. The surface of the meat dehydrates as it comes into contact with the hot metal and the surface temperature rises rapidly to above 149°C. At this point, the Maillard reaction kicks in and creates delicious new aromas, flavours and the brown colouration that gives the reaction the name we see in cookbooks – “browning”.

This is the reason that chefs allow meat to dry in the refrigerator for a few hours before cooking or pat it dry with paper towels. Salting meat also draws out water via osmosis, so you should do this either 45 minutes before cooking or just before putting the meat in a pre-heated pan so that osmosis doesn’t have a chance to occur. Dry brining combines these two techniques. With this method, chefs salt the meat thoroughly, then place it in a refrigerator to air dry for several hours or overnight. You finish up with a steak that’s well-seasoned yet has a dry surface, so it’s in an optimum condition for the Maillard reaction to take place as soon as it hits the skillet.

 

 

Sugars and proteins

The Maillard reaction requires heat, time and the correct moisture level to get going, but it also needs sugars and proteins. Some types of protein are susceptible to the Maillard reaction and will bond readily with sugars. But not with complex sugars: their molecular are too big. Reducing or simple sugars are needed to attract the chains of amino acids at specific levels of temperature and moisture.

The Maillard reaction needs a somewhat limited set of sugar and protein molecules to start with. As they mingle and bond over time, new molecules are formed and join the reaction, creating delicious new aromas and flavours.

 

The Maillard reaction: the scientific process

First, the sugar’s carbonyl group reacts with the amino acid’s amino group, producing water plus N-substituted glycosylamine.

The glycosylamine then undergoes the Amadori rearrangement to form ketosamines

The ketosamines can react further in various ways:

  • Water and reductones may be produced.
  • Aspirin, diacetyl, pyruvaldehyde and various other products of hydrolytic fission may be formed.
  • Brown nitrogenous polymers and melanoidins can be produced – the Maillard reaction.

Key points:

  • Pentose sugars are more reactive than hexoses, which are more reactive than disaccharides.
  • Different levels of browning are produced by different amino acids.

 

Why do we love the Maillard reaction so much?

It’s all about our evolution. Cooking is science; grilling, barbecuing and roasting allow us to digest foods that our bodies wouldn’t otherwise be able to process. This has given us an evolutionary edge – and the Maillard process lets us know when we have something good on our plates.

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