September 20

What is the Maillard Reaction? The Delicious Facts

Written by: Michael

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Being an avid foodie and food scientist, I can’t help but obsess over things like the Maillard reaction. Can you imagine steak without that juicy, flavor-packed sear? Can you imagine coffee without its unmistakable roasted notes? The Maillard reaction is the prime culprit for creating the irresistible flavors we crave in cooked foods.

With this in mind, why do we spend such little time trying to manipulate it? Wouldn't it make sense to take the reaction responsible for some of the most sought after and mysterious flavors in the world, and bend it to our liking?

Of course we would. The problem is....

it's too complex.

But I believe it's possible to use the little we know to alter our dishes and create flavors that truly change the kitchen game. 

So how do we manipulate this reaction for our benefit? 

Well, it depends on what you're cooking. Experimentation will be a critical aspect of harnessing this reaction to the benefit of taste (or nutrition). My hope is to shed some light on this mysterious reaction and to provide you the necessary knowledge to control it to your liking. First, let's go over the basics so you can get a solid understanding of what is needed to make this reaction happen.   

***This article goes relatively deep into the Maillard reaction. I made it this way to accommodate people of all interest levels. Most of the information below is unnecessary for learning the ways to control the maillard reaction. If you're simply looking for the backbone knowledge to increasing or decreasing the rate of the Maillard reaction in your cooking regime, look for the blue highlighted sections***

burger-maillard-reaction

-What is the Maillard Reaction?


The Maillard reaction is a non-enzymatic chemical reaction between an amine group (usually protein or amino acid) and a reducing sugar, resulting in a diverse set of brown pigmented, and non-pigmented, flavor and odor molecules. 

Although understanding the Maillard reaction for reasons of curiosity is fantastic, taking this knowledge and implementing it into the kitchen is the real goal here. 

It should be noted, the Maillard reaction is one of the most mysterious reactions in food science. It is by far one of the most taken-for-granted, least understood reactions in the world.   

Food Browning (A General Guide)


Let's put this reaction into context. There are generally 2 types of food browning; enzymatic browning and non-enzymatic browning. These are not the only definitive ways food turns brown, but are the major contributors to the browning reactions we are accustomed to.

1) Enzymatic Browning

In order for enzymatic browning to occur, you essentially need 3 variables: 1) A present enzyme capable of catalyzing the browning reaction, 2) substrates the enzyme is capable of reacting to, and 3) an environment suitable for the reaction to take place.

Let’s take the browning of apples for example. Apples contain the enzyme polyphenol oxidase and its corresponding substrate, polyphenols. The third variable needed for this reaction to take place is oxygen.  

browning-apple-enzymatic-browning

So the reaction only takes place when the inside of the apple is exposed to oxygen (or another suitable oxidizing agent). Hence, when you cut an apple open and leave it out long enough, the brown pigment on the inside becomes apparent relatively quickly.  

Browning, in this sense, usually evokes a negative response due to the taste and appearance of the brown compounds created.

2) Non-Enzymatic Browning


The two most well known cases of non-enzymatic browning are the Maillard reaction and Caramelization. Let’s go over what each one entails.

-Maillard Reaction Vs Caramelization

a) Caramelization: Caramelization requires 2 variables; sugar (reducing or nonreducing) and very high temperatures. No sugar behaves the same, but for all intents and purposes, let’s focus on cane sugar (sucrose).

When placed under conditions over approximately 320 degrees Fahrenheit, the high input of kinetic energy (temperature) allows the sugar molecules to engage in reactions it otherwise would not. 

creme-brulee-caramelization

Exposed to this heat, sucrose molecules hydrolyze into their constituent glucose and fructose molecules with the help of nearby water. These molecules then participate in a long chain of highly complex reactions eventually leading to the very sweet candy caramel we so love and cherish. 

Don’t be misled by how simple it is to make caramel. The reactions involved have been studied for decades and are still highly unidentified.

b) The Maillard Reaction requires 4 variables to take part at a noticeable rate: an amine group (Protein or amino acid usually), a reducing sugar, sufficient heat, and a suitable chemical environment (more info on these below). If you’re ever curious to know if something can take part in the Maillard reaction, ask yourself:

1) Does it have protein?

2) Does it have reducing sugars? (explained below)

When an amine group comes into contact with a reducing sugar, the Maillard reaction can take place. This results in sweet, predominantly brown pigmented flavors we find in cooked/roasted foods. There are hundreds of these brown compounds that all contribute their own distinct flavor. When tasting products of the Maillard reaction, you’re usually not just tasting a few compounds, but the flavor contribution of hundreds of reactions! COOL RIGHT?!

Barbecue-meat-Maillard-reaction

Maillard Reaction Criteria


So why isn’t the Maillard reaction happening with our steak sitting in the refrigerator? It contains both reducing sugars and proteins, right?

Well yes, but without the right heat and water activity, the Maillard reaction is an extremely slow moving process. So slow in fact, the browning effect would be nearly impossible to distinguish. 

Maillard Reaction and Temperature

The sweet spot for Maillard reactions tends to be between 280-300 degrees Fahrenheit (not universal at all). This is the temp where proteins tend to denature (unfold) sufficiently to better expose the amino groups responsible for the Maillard reaction (see below). This temperature range will vary depending on which proteins and reducing sugars are participating, amongst other factors, but for the sake of cooking this is where the reaction tends to take off.

Roughly every 10 degree Celsius increase in cooking temperature (after the Maillard temp threshold is met, which is different depending on what you're cooking) doubles the rate of the Maillard reaction (Brady, 103). So the hotter you cook, the more rapidly the Maillard reaction takes place. Be careful, if you go too hot, you’ll head towards caramelization and the irreversible pyrolysis reaction (burning). 

These aren't necessarily bad reactions. In some cases they can actually accentuate the umami flavors of the maillard products. 

Maillard Reaction and Water Activity

In order for the Maillard reaction to occur at a noticeable rate, the water activity in the food must be relatively low. Not zero, but low. Water creates mobility and allows sugar and amines to collide. But too much water and the forces of the reaction’s equilibrium and water’s evaporation temperature (212°F or 100°C) will withhold the reaction from carrying forward swiftly. Here’s how…

a) Equilibrium: Water is an end product of the first reaction involved in the Maillard reaction. Due to Le Chatelier’s Principle of equilibrium shifts, if too much water (product) is present, the reaction will tend to go in the reverse direction (towards reactants).

b) Water’s boiling point: If the food has a high water activity, much of the food is taken up by water. If the food is mostly water and water’s boiling point is 212°F, that’s roughly 60° below where the maillard reaction tends to take off. In other words, water is taking up much of the heat being added, but will not reach above 212°F. Also, as water evaporates, it has to overcome the heat of vaporization energy barrier which, when it occurs, creates cool spots on the food. 

What is Water Activity? The water activity level is the proportion of free (untethered) water in a food item. Untethered means the water is not engaged in some kind of intermolecular forces that could withhold it from reacting or phase changing. Moisture content is the amount of total (tethered and untethered) water in a food item. There is usually never a huge difference between the two, but the distinction is important.

If you're still unclear, don’t worry too much about water activity. The important takeaway is understanding the trend between moisture level and the rate of the Maillard reaction.   

Water activity Vs moisture content

Summary: The water level in the food needs to be low in order for the Maillard reaction to noticeably take place. So if you want to speed up the reaction, dry out the food. If you wish to slow down the reaction, increase the moisture level, but don't go too dry. Excessively low moisture will cause less molecular mobility, and decrease the chance of reducing sugar and amine groups colliding. 

The Maillard Reaction and pH


The Maillard can take place at many pHs. There are some trends worth mentioning. 

Alkaline environments have proven to speed up the Maillard reaction(1). This is thought to be due to the imine product formation illustrated below (Reaction 2 mechanism). A base is responsible for stealing the hydronium ion (H+) from the former amine-group's nitrogen, which allows the imine to form. The imine is a critical molecule in creating the Maillard reaction products.  

Acidic Environments have proven to slow the Maillard reaction down(1).  As detailed above, a lower pH implies a lower/nonexistent level of base. A base is needed to form the imine product essential for the Maillard reaction to carry forward. 

Alkaline environments increase the rate of the Maillard reaction and acidic environments slow them down. To increase the Maillard browning rate, add food safe bases to your dish (baking soda). To decrease the rate of Maillard browning, add food safe acids to your dish (food safe wines and vinegars).

Which Proteins React in the Maillard Reaction?


Let's bring it back to the basics.

Proteins are chains of amino acids. Amino acids are amine containing groups that differ from one another based upon their constituent R group.   

Amino-acids-and-polypeptide-example

Illustration made possible by Marvin Sketch

- Any free (non-protein bound) amino acid has a primary amine group, and therefore, can take part in the Maillard reaction. (This is why protein powders can be subject to unwanted Maillard reactions if exposed to enough moisture. They are full of free amino acids and can easily take part, given the right environment).

Primary-secondary-tertiary amines

Illustration made possible by Marvin Sketch

But...

if the amino acid is still connected to a protein via polypeptide bond, there are only a few recorded amino acids that can react while attached. This research is ongoing, and this list may have expanded by the time you read this. But for now, here is what we know:  

-Lysine is the most notorious reactor because it is a primary amine and therefore, the reacting nitrogen is very exposed and capable of engaging in the Maillard reaction. 

-Proline is a secondary amine but can still engage in the Maillard reaction, just at a much slower rate.

-Arginine can engage in the Maillard reactions but slower than the rate of lysine and proline. 

-Tryptophan is not very reactive, but can, under the right conditions take part in the Maillard reaction.  

-Ammonia is not an amino acid in the accepted sense of the word, but has a primary amine group and therefore can easily take part in the Maillard reaction. 

You can begin to decipher the Maillard flavor patterns as they relate to the amino acid/protein composition of the food being cooked. Yes, In many cases, this is a HUGE maybe! This reaction is highly complex and can turn your 20 amino acids into hundreds, if not thousands, of flavor compounds. But patterns can still definitely be uncovered.  

Free Tryptophan, for example, can take part in the maillard reaction and create some familiar flavors. Soy sauce is filled with free tryptophan, and the maillard products are thought to give soy sauce its' distinctive umami flavor (Brady 210).  

Which Sugars React in the Maillard Reaction?


As stated above, only reducing sugars can engage in the maillard reaction. 

So what is a reducing sugar?

A reducing sugar is a sugar molecule capable of being reduced or oxidized. Sucrose and Trehalose cannot be reduced or oxidized because they do not contain free aldehyde or ketone groups. Hence sucrose and Trehalose do not engage in the Maillard reaction. They can although, in the right conditions, be broken down into their constituent monosaccharides which can engage in the Maillard reaction. 

Disaccharides like lactose and maltose do contain free aldehyde and/or ketone groups in their chemical structure, and therefore are reducing sugars and can engage in the Maillard reaction.

Reducing sugars are the only sugars that engage in the Maillard reaction.

Examples of Non-Reducing sugars (No Maillard): Sucrose, Trehalose

Examples of Reducing Sugars (Maillard): Glucose, Fructose, Ribose, Xylose, Lactose, Galactose 


Maillard Reaction Chemistry

It should be noted that understanding the mechanics of the chemistry is not super important. The main takeaway is to identify where acids, bases, and water catalyze reactions. You can use this knowledge to manipulate the speed and duration of the reaction. I'll explain more as we carry on.  

Here are the basics of what we know regarding the chemistry of the maillard reaction. 

Reaction 1:

Cyclic to Linear Reducing Sugar isomerization reaction 

Maillard-reaction-chemistry

Illustration made possible by Marvin Sketch, Reactions extracted from Brady, J Introductory Food Chemistry

Glucose is constantly going through an isomerization reaction between its cyclic and linear form. As the arrows imply, the equilibrium is high favored towards the cyclic form. Weird as it may be, the linear form of the sugars are the only ones participating in the Maillard reaction. But as these few molecules react, the equilibrium continually shifts forward, providing a constant supply of linear sugars. 

Takeaway from Reaction 1: Heating the sugar creates an unstable chemical environment and allows for the creation of more linear sugar. Linear sugar is the only sugar taking part in the Maillard reaction. So again, to increase the rate of the Maillard reaction, increase the heat.   


Reaction 2: 

Amine and Reducing sugar React to form an Imine 

Maillard-reaction-chemistry

Illustration made possible by Marvin Sketch, Reactions extracted from Brady, J Introductory Food Chemistry

When the reducing sugar and amine collide they eventually form an imine and give up a water molecule in the process. 

Proposed Mechanism:

Maillard-reaction-mechanism

Illustration made possible by Marvin Sketch, Reactions extracted from Brady, J Introductory Food Chemistry

Takeaway From Reaction 2: Water is a bi-product of this reaction. Due to Le Chatelier’s Principle of equilibrium shifts and water's low boiling point, less water means faster Maillard reactions. A base is needed in order to create the imine product. This is why putting the food item in contact with something basic will push the reaction forward faster. 


Reaction 3:

Imine Rearrangement to form Amadori and Aminoenol Products

Amadori-Reaction-Maillard-Browning

Illustration made possible by Marvin Sketch, Reactions extracted from Brady, J Introductory Food Chemistry

Proposed Mechanism:

Maillard-reaction-mechanism

Illustration made possible by Marvin Sketch

Takeaways of Reaction 3: As you can see, both acid (H+) and Base play critical roles in perpetuating this reaction forward. It is thought that excess acid composition still slows down the rate of the reaction because the excess H+ ions interfere with the reaction more than they push it forward.   


Reaction 4 (Aminoenol pathway): 

Aminoenol Reacting to Form Brown Pigmented End-products

Maillard-reaction-brown-pigments

Illustration made possible by Marvin Sketch, Reactions extracted from Brady, J Introductory Food Chemistry

Takeaway from Reaction 4: Bisulfite comes in salt forms like sodium bisulfite. You'll see this on the ingredients list of a lot of dried foods with a long shelf-life. This helps to reduce the Maillard reaction in shelf stable food where we typically don't want it happening.  

Reaction 4 (Amadori pathway) 

Aminoenol Reacting to Form Brown Pigmented Endproducts

Maillard-reaction-brown-pigments

Illustration made possible by Marvin Sketch, Reactions extracted from Brady, J Introductory Food Chemistry


Maillard Reaction in Familiar Dishes


Maillard Reaction in Steak:

Steak-Maillard-Reaction

Ahhhh yes, one of my favorite dishes, and yet one that perfecting has been the bane of my existence. Cooking steak is one of the most fun and delicious cooking experiences in the kitchen. 

Here are some Maillard concepts to keep in mind as you cook your steak. 

1) The only part of the steak where the Maillard reaction really takes off is the outside. This is the point where the temperature and moisture level reach an ideal Maillard browning point. So stop trying to "Maillard" the inside of your steak. By the time you pull it off, your steak will be a dry, tasteless slab of meat. 

2) The efficacy of pre-salting your steak is quite the controversy in the BBQ world, but the logic makes sense. Adding salt beforehand pulls moisture out of the steak, drying the outside to allow for a faster sear (faster Maillard Products). Pre-salting, and taking time to allow osmosis to do its work (necessary salt rest-time depends on size of the meat), also pushes the salt farther into the steak making for a more uniformly salted meat. 

3) As far as temperature, the Maillard reaction tends to kick into high gear with the steak around 300°F and caramelization around 400°F. I find the best of both worlds happens right at 350°F. Keep in mind, pan temperature does not equal steak temperature, so an infrared thermometer might do you some good. Caramelization will result in sweeter flavors, whereas the Maillard reaction will make some more complex, yet still sweet umami flavors.  

Maillard Reaction in Coffee

Coffe-Beans-Maillard-Reaction

Ever brewed a pot of un-roasted coffee beans?

Good, never do it!

The roasting of coffee beans is the only reason coffee is a palatable beverage. Roasting enables the Maillard reaction to create sweet, roasted flavors that help balance the overbearing bitterness of the bean. But the Maillard reaction isn't the only player here. Caramelization, and even pyrolysis (burning) play critical roles in providing the sweet and acrid flavors coffee is so well-known for. The processing of coffee beans from tree to brew is a lengthy and complicated process. If you're interested in learning more, check out Coffee Chemistry's extensive coffee science site.   

Maillard Reaction in Bread

It should be relatively obvious, but there is a reason people prefer the taste of a loaf over a slice of bread. Loaves have a larger surface area of crust, and crust is the primary place where the Maillard reaction takes place.    

Bread Loaf

Mailard-Reaction- Bread

Loafs have a larger crust, thus have a larger proportion of Maillard reaction products. 

  Vs.

Bread Slice

Bread-Maillard-reaction

Sliced bread has less crust, thus less surface area of Maillard reaction products. 

The Maillard browning of bread happens during the baking stage. As the bread bakes, the outside of the bread dries out and hits the optimal temperature and water activity for the Maillard reaction to take place.   

Maillard Reaction in Beer

Ever wonder how your pilsner pulls of those awesome toasty notes? Or maybe how that robust stout carries those roasty tones? Well, these flavors and aromas primarily come from the malt, which is the result of Maillard products from the baking/roasting of certain grains. 

Malt is essentially the baking of germinated barley seeds to create different variations of Maillard flavors. The barley is steeped in water, allowed to germinate, and then kilned (heated) to the desired color, where it then becomes chalk full of Maillard products ready for extraction. This malt is then distributed to breweries where it is milled and placed into the hot mash tun water. The hot water gelatinizes (solubilizes) the constituents of the malt and the maillard flavors are extracted into the soon-to-be wort (sweet water to be fermented into beer). 

Negative Consequences of the Maillard Reaction


Although it creates some of the flavors we consider to be the most attractive in the world, the negative nutritional outcome of the Maillard reaction shouldn't be neglected. By creating the environment for the Maillard reaction, you are essentially denaturing proteins, allowing them to react and make products that do not have the same nutritional value they once did. You could say the Maillard reaction is an exchange of nutrition for better flavor. 

This is debatable. The act of heating helps to make many of the complex molecules of meat more digestible. 

The upside to this nutritional loss is that the Maillard reaction is usually happening on a very limited scale due to the very specific environmental requirements it has. This only really becomes problematic when we're talking about foods with a lot of exposed surface area. Protein powders, for example, are dry enough to take part in the Maillard reaction if given the right heat and moisture. So keep your dry powders away from the sun to avoid protein degradation. 

Maillard Reaction and Cancer

There has been a lot of speculation on the recent discovery of acrylamide in particular foods subject to heat treatment. Acrylamide is thought to form when arginine, one of the 20 amino acids found in many foods, takes part in the Maillard reaction with nearby reducing sugars (2). Various studies have linked prolonged exposure to acrylamide with cancer and this has provoked a lot of controversy in the food science industry (3). 

The question isn't whether or not this reaction produces acrylamide; we know it does. The question is whether this long term micro-dosing of acrylamide through Maillard foods will have negative consequences on health. Honestly, at this point the research just isn't there. My advice to anyone is to eat these foods in moderation. There are also some precautions you can take in order to decrease the chance of major acrylamide exposure when eating certain foods. 

Foods Known to Have Acrylamide:

1) Fried, baked, roasted potatoes

2) Fried, baked, roasted grain products

3) Fried, baked, roasted meat products 

4) Coffee

Ways to Avoid Excess Acrylamide

1) Keep potatoes out of the fridge. Cooking refrigerated potatoes leads to higher levels of acrylamide. 

2) Steam foods instead of baking, frying or roasting. This keeps temperatures low enough to avoid major Maillard browning.

3) If you must bake, fry or roast, shorten the period of cooking as best you can. The longer the food item is in an environment that fosters Maillard products, the higher potential for Acrylamide build up. 

Conclusion


You're probably wondering why I took the time to write this monster of an article when I could've just given you the tricks of speeding up or slowing down the maillard reaction in a few short paragraphs. 

The thing is, I'm fascinated by this reaction. It is one of those concepts we completely take for granted and yet has a profound impact on the quality of our life.  

Why does the maillard reaction makes things taste so good? Why does the maillard reaction create so many variations of flavor? Couldn't we have just gotten along fine with a few less flavors?

I have my theories, but at this point I just want to experience it from every angle I can.

Hopefully you do as well.

Any which way, thanks for listening.

If you have any thoughts, I WOULD LOVE TO HEAR THEM!! 

Comment Below!

Michael 

Founder of Robust Kitchen

 


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About the author

Michael spends his days eating, drinking and studying the fascinating world of food. He received his Bachelors Degree in Food Science and Technology at the University of California, Davis and spent much of his time at the school brewery. While school proved to be an invaluable experience, his true passion lies in exposing the hidden crannies of food for the cooking laymen.

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