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Fresh baked bread, roasted potatoes, seared steak, toasted marshmallows, chocolate, a fresh cup of coffee. What do these foods have in common?
Their characteristic tastes and aromas are a result of the Maillard reaction.
Though technically a series of reactions, the Maillard reaction (pronounced “my-ar”) happens when protein and sugar react, transforming these nutrients into golden brown, aromatic chemical compounds.
Chances are you manipulate the Maillard reaction often if you like to cook, whether you understand the chemistry of what’s happening or not. But don’t worry, even food scientists don’t fully understand it!
The following article is a simple introduction to the Maillard reaction and how to manipulate it in the kitchen. In it, we’ll cover the ingredients and basic chemistry of the reaction, its by-products and their nutritional value, and how cooking techniques control the outcome to achieve desired culinary results.
What is the Maillard Reaction?
Named after the French chemist, Louis Camille Maillard, who first documented the process in 1912, the Maillard reaction is the process of non-enzymatic browning of foods. (Imagine a sliced apple exposed to air for a while to get a picture of enzymatic browning.)
To get it going, the Maillard reaction requires a few basic ingredients:
- Reducing sugar
- Amino acids (aka protein)
- Heat (not required, though greatly speeds up the process)
A reducing sugar is any sugar that can act as a reducing agent. In case you aren’t reading this blog for an organic chemistry lecture, just know this: a reducing sugar is the participant in the Maillard reaction that loses electrons, which means that it becomes oxidized.
What is important to know is that not all carbohydrates are able to do this. The ones that can are mostly monosaccharides, which are single sugar molecules, such as glucose, fructose, or galactose. Some disaccharides (lactose and maltose) and some more complex carbohydrates (like those in coffee beans) can participate in the Maillard reaction because their chemical structures, like monosaccharides, can provide the necessary reaction site to donate electrons to the other participant in the Maillard reaction: protein.
Proteins are complex molecules made of many amino acids linked together by peptide bonds. The amino group (-NH2) is the important feature here, which acts as an oxidizing agent because it accepts electrons from the sugar molecule and becomes reduced.
The reaction between the sugar and the amino acid links the two molecules together, forming a larger, more complex chemical compound. As cooking proceeds, more of these linkages occur, and the resulting chemical compounds rearrange and participate in other reactions that produce unique flavor molecules.
Glucose plus the simplest amino acid, glycine, can produce over 20 different byproducts. Considering the many varieties and combinations of reducing sugars and amino acids in foods, the possibilities of Maillard reaction products is staggering. Talk about complexity!
Maillard Reaction Products and their Nutritional Value
Maillard reaction products influence the organoleptic properties of food, i.e., the aspects of food that impact sensory experience – taste, sight, smell, and touch. They can also have an impact on nutritional value. Two categories of byproducts include melanoidins and advanced glycation end products (AGEs).
Melanoidins are complex molecules produced in the late stages of the Maillard reaction. Though their chemical structures vary and are not entirely known, generally they are brown in color, have high molecular weight (that is, they are large), and contain nitrogen.
Like the nutrients of the rainbow, these molecules are not only responsible for color, but offer antioxidant properties as well. In addition, melanoidins have the potential to modulate the microbial activity of the gut, suppress tumor growth, and increase the activity of detoxification enzymes.
Not all Maillard products are beneficial, however. Undesirable consequences of the Maillard reaction include the denaturing of proteins in food, inactivation of enzymes in the digestive tract, and the pro-oxidation or carcinogenic potential of advanced glycation end-products (AGEs), such as acrylamide or heterocyclic amines. Often, AGEs form when starchy foods or meats are cooked too long or at too high heat (i.e., the Maillard reaction gone too far).
As you can see, it’s not a black and white distinction when considering the potential health effects of the Maillard reaction as so much depends on the type of food and how it’s cooked (not to mention the limitations of this sort of research). Regardless of nutritional value, Maillard products are a major factor in the way a food smells, looks, and tastes.
Where to Find Maillard Products
It is estimated that 8-10 grams of melanoidins are consumed each day in a typical diet, with the majority coming from coffee and baked goods. Other sources of melanoidins include:
- Dark beer
- Balsamic vinegar
- Roasted potatoes
- Roasted pulses or seeds
- Barbequed meat
- Soy Sauce
This list highlights the unique sensory qualities that result when reducing sugars and proteins react as they are roasted, baked, or fermented. Let’s explore at how some cooking techniques enhance, or diminish, the Maillard reaction.
Ways to Manipulate the Maillard Reaction
Heat is the most effective way to control the Maillard reaction, as high heat and/or longer cooking time creates more reaction products. For example, dark roast coffee beans produce a stronger flavor because they are heated at higher temperatures and for longer than light roast coffee beans. When making gumbo, a dark, brown roux generates more flavor by the long, slow cooking of flour and butter.
The ideal temperature for the Maillard reaction to proceed is 230-340°F (110-170°C). Temperatures above these levels might burn foods, creating AGEs and not so appetizing results.
Note that the Maillard reaction proceeds at higher temperatures than water boils (212°F or 100 °C). Therefore, the less water present, the more reaction products. Since foods contain a certain amount of water, the Maillard reaction tends to occur on surfaces, rather than the inside.
Conversely, cooking foods submerged in water prevents Maillard reaction products from forming, as contents can only get as hot as the boiling water. Adding water can also halt the reaction at a desired time, as in deglazing a pan with water, broth, or wine, to mix the browned and flavored mixture from the pan into a sauce or gravy before it turns into a burned mess.
Another way to manipulate the Maillard reaction is to strategically add sugar or protein before or during cooking.
For example, brushing egg wash on breads or baked goods before baking encourages the formation of a browned crust by adding protein to the mostly carbohydrate-based dough.
Another example is glazing a high protein food with sugar, as in brushing spiced honey onto a ham for the last bit of roasting or marinating fish or savory meats in a sweet mixture prior to cooking.
Finally, adjusting pH can either speed up or slow down the Maillard reaction. Adding an acid, which lowers pH, will slow down the Maillard reaction. Adding a base, which increases pH, will speed it up.
One example of a beneficial pH increase in baking is the Bavarian pretzel. It is believed to have been discovered by accident when a German baker brushed his pretzels with a lye solution (a base) used for cleaning instead of sugar water solution. The result was a shiny brown crust with a soft doughy inside – a smashing success that redefined the soft pretzel.
Caramelized Onions Using Baking Soda
Though caramelization and Maillard reactions aren’t the same thing (caramelization occurs between two sugars, and Maillard between a sugar and a protein), often they can occur in the same foods. Nonetheless, the following recipe is a great example of how adjusting pH can affect the speed of non-enzymatic browning reactions.
- 1 large onion, sliced (approx. 1 lb)
- 1-2 tbsp butter (or other cooking oil)
- ⅛ – ¼ tsp baking soda
- Salt to taste
Melt butter in a pan, then add other ingredients. Sauté to desired color and consistency. Use in your favorite recipe that calls for caramelized onions.
The addition of the baking soda speeds along the browning process, so that sweet, soft caramelized onions are achieved in about 10-15 minutes instead of 45. The amount of baking soda can be adjusted slightly, but exceeding ¼ tsp per pound of onions might cause the onions to throw off too much water and become too mushy.
Kitchen as Laboratory
The Maillard reaction is just one example of how food chemistry influences the sensory experience and nutritional value of food. Adjusting ingredients, heat, and pH are ways to control the production of Maillard byproducts to optimize taste and nutritional value.
Want to learn more about how to optimize cooking techniques for a fabulous culinary experience? Consider becoming a Natural Food Chef!
About the author: Karyn Lane is a recent graduate of NTI’s Nutrition Therapist Master Program. She finds her chemistry degree a useful tool in her study of holistic nutrition and loves to treat her kitchen as a laboratory for new recipes and cooking techniques. You can follow her on Instagram @karyn.aka.klaryn.
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