Stir-frying, a common cooking method in many Asian cuisines, is similar to sautéing. It requires cooking food at a high heat for a short time to maintain food texture.


Many people like to wake up to a fresh cup of roasted coffee. Perhaps they also like toast with their breakfast. For lunch, dropping in at the local Chinese place for a stir-fried cashew chicken may sound good. For many people, the convenience of coming home to the smell of a pot roast with vegetables and flavorful gravy that has been simmering all afternoon provides an easy end to a long day at work. Many others look forward to enjoying a lazy summer afternoon, while cooking some smoked brats with caramelized onions outdoors over the grill.

Cutting across all these examples of meals, cuisines, flavors, foods and methods of cooking runs a common thread...the flavors of cooking. Ever since Prometheus taught man the secret of fire, mankind has been cooking his food. Cooking makes foods easier to digest, makes many nutrients easier to absorb, preserves foods for longer storage and destroys harmful pathogens. Cooking also makes most foods more palatable to downright delectable.

It is hard to believe this vast variety of foods, from coffee to meat to vegetables to nuts, and cooking methods, from roasting to toasting to sautéing and braising to grilling, all owe many of their vast variety of flavors to only two complex chemical reactions--the Maillard reaction (also sometimes called the browning reaction) and caramelization.

Caramelization and Maillard reactions are both non-enzymatic browning reactions that occur in food chemistry. Enzymatic browning reactions, such as the cut surface of an apple turning brown or a bruise on a banana, are generally undesirable, as they are seen as a sign of damage. This is not true with these non-enzymatic browning reactions, as they are desirable signs of quality and enhance the appearance, aroma and taste of foods.  Although these two reactions are distinctly different (as described later in this article), they are often confused, as they sometimes occur simultaneously. Depending on the food, their intermediates can interact, and some of the end products are the same. Add to this complexity the variables of temperature and pH, and it becomes clear how “only” two reactions can lead to a variety of flavors across so many different foods and cooking methods.

Caramelization and Maillard Reactions

Caramelization is a complex reaction involving sugars upon the application of heat (pyrolysis). To distinguish it from Maillard browning, it does not involve amino acids, and it cannot occur at room temperature. The reaction generally does not begin with most sugars until 320°F (160°C) is reached.

As heat is applied, disaccharides decompose to monosaccharides. These monosaccharides begin to react with each other in dehydration reactions, then isomerize from an aldose to ketose, followed by additional dehydration reactions. The final steps include fragmentation, producing flavor compounds and polymerization, leading to the variety of colors associated with caramel. The greater the heat applied, the greater the polymerization, resulting in deeper colors, but eventually less flavor. With greater heat, carbonization (burning or charring) begins.

How many times has a chef on TV demonstrated how to properly sear a steak and referred to it as “caramelizing” the meat?  It is enough to make a food lover cringe! It also is a disservice to French scientist Louis Camille Maillard (1878-1936), who characterized the reaction in his Ph.D. thesis in 1912. While trying to figure out how proteins are formed from amino acids, he combined sugars with amino acids and heated them. He observed they browned in a fashion similar to food.

The Maillard reaction is initiated when the amine group of amino acids reacts with the carbonyl group of a reducing sugar to form an Amadori compound, which can isomerase into three different structures. Since there are five common reducing sugars in foods and 20 amino acids, the first step results in over 100 possible compounds. It gets more complicated after that.

Several different reaction pathways can occur at this point. The end-products of these reaction pathways result in melanoidins, which contribute the brown color of cooked food, and a complex mixture of over 600 aroma compounds. A few examples are diacetyl (buttery flavor), pyruvaldehyde (caramel-type flavor) and furfural (nutty aromas). 

One difference between Maillard browning and caramelization is that Maillard reactions do not require heat. One of the earliest observed problems with powdered milk was that it slowly turned brown during extended storage. In the absence of water, the milk proteins initiated the Maillard reaction with the lactose and turned brown. This was unacceptable to consumers, but it is the author’s opinion that consumers had not yet been introduced to dulce de leche, a great example of both Maillard and caramelization occurring simultaneously in the same food system.

While heat is not required, it does accelerate the Maillard reaction, from several minutes (in the case of a seared steak) to months (in the case of powdered milk). It is useful to explore how these two reactions relate to several cooking methods. It should be noted that all these processes involve dry heat methods, since both reactions--Maillard and caramelization--occur in the absence of water.

Roasting

Roasting is a dry heat method (no moisture added) that uses relatively higher temperatures and longer times. During this process, excess moisture is driven away, and both Maillard browning and caramelization occurs, depending on the composition of the food. Larger cuts of meat are usually roasted, with the outer layer developing a lot of flavor from Maillard reactions, while the heat penetrates the interior of the meat.  Rotisserie is considered a style of roasting that involves turning the food on a spit to expose all sides evenly to the heat source. Many other foods can be roasted, including potatoes and vegetables. In these instances, there is a greater contribution of flavor from caramelization reactions. Coffee and chocolate also are roasted, while they are still beans.

The classic brown stock owes its flavor to browning reactions. The process begins with bones with some meat, contributing the precursors for the Maillard reaction, and mirepoix, a blend of onions, celery and carrots that provides carbohydrates for caramelization. These chemicals are then extracted into simmering water, and the solids are filtered out and discarded. It may then be concentrated into demi-glace, which may be shelf-stable, depending on the water activity achieved. Further browning reactions can happen in this concentrated mixture, so refrigeration may be necessary to prevent additional flavor changes, not as much for food safety concerns.

Baking is similar to roasting, except the term is generally applied to breads and pastries.  These foods are higher in starch and, therefore, owe more flavor to the caramelization reaction.

Sautéing

Sautéing is another dry heat method (again, it requires no water) in which a minimal amount of fat is added. The food quantity is generally much smaller, allowing a greater surface area to develop flavor, while exposing the food to shorter cooking times. Because this is a direct heat method, cooking times generally are much shorter than roasting.  Searing a steak can be considered a type of sautéing, with the steak contributing the fat.

This cooking process still relies on Maillard and caramelization reactions, but the added fat contributes additional flavors from being exposed to this intense heat, as well as undergoing its own complex series of chemical reactions.

Stir-frying, a common cooking method in many Asian cuisines, is similar to sautéing but, generally, the heat is higher and the cooking times shorter to maintain the food’s texture; however, there is less time for flavor development.

Braising and Grilling/broiling

Braising is a blend of dry heat and moist heat methods. The food (generally meat) is first cooked with a dry heat method (broiling, grilling, searing) to develop the cooked flavors, then some water is added and the food is allowed to simmer, extracting those flavors into a sauce that is served with the food. The chef is, essentially, making a brown stock at the same time he is cooking the food. Pot roast is a classic example of a braised entrée, in which the longer cooking times and moist heat improve the texture of the meat, while one can still enjoy the flavors of cooking.

Grilling is another dry heat cooking process in which the food is cooked directly over a flame. Besides the browning reactions that occur, the fat dripping from the food is pyrolyzed and vaporized in its own complex reaction, then absorbed by the food above.  Even vegetables develop this grilled flavor, since they often are coated with fat prior to cooking to prevent sticking. Broiling is similar to grilling, except the heat source is above the food, rather than below. This prevents the flavor development of the dripping fat being added to the foods.

These cooking methods are generally time-consuming and energy- and labor-intensive. They require more highly trained line operators, and it is difficult to apply adequate quality control. The flavor industry has come up with several solutions to assist product developers to mimic the traditional cooking methods described above--without the complexity of incorporating these cooking methods into the manufacturing process.  These flavors generally are referred to as reaction flavors, or process flavors.

The flavor chemist generally starts with familiar ingredients that provide the same chemical composition that would be found in food. For caramelization reactions, all that is required is a sugar. The formula can start with a single sugar, a blend of sugars or even similar sugars from different sources, such as interchanging corn syrup, rice syrup or wheat syrup to produce different profiles. The main process control is the time-temperature profile.

These caramel flavors can be used in a wide variety of savory applications, including stocks, broths and soup bases, and to enhance grilled vegetable notes. More highly reacted caramel flavors can be used to mimic roasted meats, coffee, chocolate and even substitute for molasses.

To create Maillard reaction flavors, sugars such as sucrose, fructose, dextrose or lactose are used and combined with an amino acid source, such as stocks, broths, HVP or soy sauce for vegetarian flavors. Meat could even be a starting material, but it is expensive and often requires a USDA certification in the U.S. Other ingredients may be added to control important factors, such as pH and water activity.

These starting materials are then “reacted” under carefully controlled settings of time, temperature and pressure to achieve the desired flavor. Temperatures range from 230-300°F or higher, with times ranging from a few hours to 18 hours for Maillard reaction flavors. Just as with the cooking methods, a longer time and higher temperature produces stronger, roasted notes.  Reactions with shorter times and lower temperatures will provide notes similar to a braised product. A higher ratio of sugar would imitate caramelization reactions, similar to cooked notes in starchy vegetables, where higher ratios of amino acids allow for more Maillard reactions and more cooked meat flavors.

Once the flavor has been created by following the carefully monitored formula and procedure, it can then be compounded with other ingredients, even other reaction flavors, to create the exact profile needed for a specific application. Some ingredients may include lipolized butter oil (LBO) or diacetyl to enhance the buttery notes to mimic a product sautéed in butter. Flavor enhancers such as salt, MSG, ribotides, yeast extracts, or various seasonings or spices can be added. To mimic an Asian stir-fry, the flavorist may add toasted sesame oil and soy sauce. In some cases, it is important for the product developer to understand how the corporate chef prepared the gold standard. Was the food grilled or broiled? Knowing this information can guide developers in determining if they want to add a grill flavor to the flavoring (if it was grilled) or not (if it was broiled).

One of the great things about these flavors is that they allow the product developer to create foods that could not be created in the kitchen by a chef. For instance, a potato chip cannot really be flame-broiled, but one fast-food company has branded a flame-broiled flavored potato chip. Vegetarian dishes that appeal to meat-eaters in a split household, without using meat, also can be created. Or, how about a kosher bacon-cheddar-flavored potato chip seasoning? (The author developed the recipe during his first job in the food industry.) pf

Website Resources:

PreparedFoods.com -- Type in the words “grilling” and “roasting”
www.food-info.net/uk -- A general website on ingredients, foods, how they are made, food safety and more
www.OnNetworks.com -- Features a short video on YouTube on browning reactions; click on “food science” and then “The Maillard Reaction”
www.cookinglight.com -- Click “Cooking 101” and then type “grilling”
Gisslen, Wayne. Professional Cooking. 6th Edition.  Hoboken, N.J.: John Wiley & Sons, 2007.