The Science behind a Good Meaty Steak

By Jack Scott

We know from observation and experience, that when you cook food, it changes colour, releases aromas, and transforms the taste. Common sense would say that when exposed to heat, something is clearly happening at a chemical level to change the product. But what exactly? And is the same for all foods? 

Louis-Cammile Maillard

In the early twentieth century, a scientist named Louis-Cammile Maillard noticed that when he heated sugars and amino acids together, the mixture slowly turned brown. What he had discovered was the Maillard effect (What a coincidence!) This reaction gave a scientific explanation behind what everyone intrinsically knew, that as food is cooked, it changes it's colour, taste, and chemistry. It wasn't until 1953 however, when an american chemist published a paper on the subject, that a mechanism for the Maillard reaction became established(1). 

The Maillard reaction is not a single reaction, but a complex series of reactions between amino acids and reducing sugars, usually at increased temperatures. 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(3).

The breakdown of Sugars and Amino Acids which produce the Maillard Reaction

If we take meat as an example, the denatured proteins on the surface of the meat recombine with the sugars present. The combination creates the "meaty" flavour and changes the colour. For this reason, it is also called the browning reaction. When meat is cooked, the outside reaches a higher temperature than the inside, triggering the Maillard reaction and creating the strongest flavours on the surface(1). The Maillard reaction occurs most readily at around 200° C, although in the case of marinating, the acids in the marinade can 'cook' the outer surface of some meats.

The meat has been changed by the Maillard reaction, whilst the onions have been caramelised.

Maillard reactions are (partly) responsible for the flavour of bread, cookies, cakes, beer, chocolate, popcorn, cooked rice. In many cases, such as in coffee, the flavour is a combination of Maillard reactions and caramelisation. Caramelisation is the browning of sugar, a process used extensively in cooking for the resulting nutty flavour and brown colour(2). As the process occurs, volatile chemicals are released, producing the characteristic caramel flavour. Like the Maillard reaction, caramelisation is a type of non-enzymatic browning. However, unlike the Maillard reaction, caramelisation only takes place above 120-150 °C, whereas Maillard reactions could occur at room temperature.

Although studied for nearly one century, the Maillard reactions are so complex that still many reactions and pathways are unknown. Many different factors play a role in the Maillard formation and thus in the final colour and aroma; pH (acidity), types of amino acids and sugars, temperature, time, presence of oxygen, water, water activity (aw) and other food components all are important(4).

1 http://www.exploratorium.edu/cooking/meat/INT-what-makes-flavor.html

2 http://www.exploratorium.edu/cooking/candy/caramels-story.html

3 http://www.food-info.net/uk/colour/maillard.htm

4 http://web.archive.org/web/20041029235215/http://www.agsci.ubc.ca/courses/fnh/410/colour/3_82.htm