The Maillard Reaction
Of all the reactions discussed so far,
the Maillard reaction is perhaps the
godfather of all browning reactions.
Though the reaction is typically
associated with food, its true origin is
actually deeply rooted in the medical
field. In 1900, Dr. Louis Camille
Maillard embarked on solving one of
life’s most complex questions: how does
the human body create proteins? His
early attempts to solve this involved
combining isolated amino acids in vials
and agitating, with no luck. When he
combined reducing sugars (glucose) and
subjected the same amino acid mixture
to heat, he was stunned. As heat was
applied to the mixture, the solution
slowly changed from a clear liquid to a
brown solution, giving off nutty/bready
aromas—essentially marking the
discovery of the Maillard Reaction. Since
then, hundreds of manufacturers have
tweaked the reaction, and it now serves
as a source for aroma development
within the food industry. But it wasn’t
until after World War II—when soldiers
complained that their powdered eggs
were changing color and producing
off-flavors—that the military seriouslybegan to study the reaction in detail.
Fifty years later, we’re still unlocking the
mystery of this complex reaction. Though
the reaction still plays an important role
in food, in recent years it’s also become a
topic of great interest in the medical field
since it’s believed to be involved in the
aging process.
In essence, the Maillard reaction isthe process whereby available amino
acids and sugars combine in thermally
processed food. We’ll discuss details later,
but it’s essentially the reaction responsible
for producing the aroma and flavor in
products such as toasted bread, steak
and coffee. Its been estimated that in
steak and coffee alone, more than 600compounds combine to create their complex aroma. And though
extremely complex, what we’ll discuss next is simply a layman’s
introduction to the Maillard reaction, as a comprehensive
explanation would be outside the scope of this article.
In a nutshell, the Maillard reaction can be summarized in
four major steps: In step one, amino acids combine with sugars
to form several N-glucosamine compounds during roasting.
Since these compounds are relatively unstable, they typically
undergo a second set of reactions—Amadori or Heynes—to form
several other intermediates (step two). Up until this point, all
the compounds produced are colorless and lack any detectable
flavor. But it’s not until we reach step three, or the Strecker
degradation, where a handful of N-glucosamine (those with
double bonds created in step one) react with other amino acids
to form compounds we typically associate with coffee aroma.
Pyrazines and pyridines, which typically have maize/nutty/bitter
aromas, and many other compounds are produced in this step.
And finally, in step four, all remaining intermediates combine to
form long chains of brown-colored melanoidins—the compound
responsible for a coffee’s color.
There are a number of factors that affect the Maillard
reaction, including moisture level, pH and temperature. Since
water is produced in the combination of amino acids with sugars,
products with excess water activity actually impede the reaction.
So for those products such as bread, powdered milk or powderedeggs, which already have a low water activity, browning occurs
much more quickly. Also, the reaction accelerates in alkaline
environments (pH greater than 7) and varies with the type of
sugar and amino acid present. Though some of these factors may
be out of our immediate control, the one thing we can control is
temperature. According to empirical data, it’s been shown thatthe Maillard Reaction doubles for every 10-degree increase in
temperature. Interesting, but anyone who has ever taken a roast
past second crack can easily attest to this. Why?