That grill master may be a master of chemistry

Editor’s Note:

Barbecue is nature's gift to mankind. Chemical reactions are what make this barbecue perfect.

The night when our ancestors said goodbye to eating raw meat and drinking blood must have been because of an unexpected lightning. The lightning struck the dense pine needles in the pine forest, igniting a raging fire. A slightly fat antelope under the tree was trapped by the fire before it could run away, and the distance between it and the fire was just right - if it was a little closer to the fire, it would explode, and if it was a little closer, it would melt... When the fire faded but there was still some residual heat, our ancestors picked up the crispy lamb leg and took a bite. The texture and freshness burst out in their mouths and froze in the beautiful moment, and from then on, they decided to encode in their genes the crazy admiration for barbecue.

Even in modern society, people's diet has been rich and colorful beyond our imagination, and barbecue is still an important choice for business banquets, friends' gatherings, relatives bragging, and couples' dates. Barbecue is so addictive that it even triggered a human migration to Shandong in 2023. The small brazier and small burrito are special, but for the essence of barbecue, the more addictive thing must be the cooked meat itself.

What is a perfect barbecue? A slightly golden, charred skin, rich and juicy meat fibers inside, full of aroma and fat... It is a wonderful feast of chemical reactions, a culinary synthesis of heat, taste and flavor created by protein, fat, charcoal and seasoning. So how to get a perfect barbecue? This may be a cooking problem or a marketing problem, but more fundamentally, it should be a chemical problem.

Now, let's cook.

Part 1

Origin: Maillard reaction, the beginning of flavor and taste

Whenever we talk about chemistry and cooking, we will inevitably mention Maillard. Although it is a bit cliché, the academic community has not yet fully understood what the Maillard reaction is. The Maillard reaction is named after French physicist and chemist Louis-Camille Maillard (1878-1936). Maillard published an article in 1912 discussing the phenomenon of brown pigmentation on the surface of meat between 140℃-165℃[1]. Although Maillard took the naming rights, the chemical reaction mechanism of the Maillard reaction was first proposed by American chemist John Edward Hodge (1914-1996) in 1953[2]. This article, titled "Dehydrated Foods, Chemistry of Browning Reactions in Model Systems", was later selected by SCI as a Citation Classic. Hodge explained the process based on a series of reactions between sugars and amino acids, which eventually converted into melanoidins (or Maillard bodies).

Melanoids are a series of nitrogen-containing polymers that have a caramelized taste and texture. Melanoids will break down during continuous heating to produce hundreds of small molecules with different aromas. These substances, which contain nitrogen or aromatic rings, will become the most attractive components of the barbecue flavor.

Even if we do not intend to delve into the details of the chemical transformation in this article, we can keenly feel from the transformation route shown in Figure 1 that temperature, dehydration rate, pH value, type of sugar, etc. are the key to regulating the Maillard reaction path and degree of progress.

Figure 1 The Maillard reaction mechanism proposed by Hodge. Image source: Reference [3]

There are many types of Maillard reactions, which compete with each other. Therefore, the practical process of barbecue requires temperature control, which regulates the path of the Maillard reaction and obtains different melanoidins and subsequent barbecue flavors. The temperature cannot be too high, which will cause surface carbonization (no one wants to eat meat skewers that have turned into inorganic substances); the temperature cannot be too low, which will cause the Maillard reaction to proceed smoothly and the flavor to be poor [4]. Dehydration reaction also affects the final melanoidin substance. Dehydration can be controlled by temperature control on the one hand, and by brushing oil to prevent rapid water loss and obtain a different taste. In addition to oil, different seasonings are often brushed on the skewers. These seasonings will change the pH value of the surface of the skewers, thereby affecting the chemical composition of the Maillard products and controlling the final taste details of the skewers.

In some regions, barbecue chefs sprinkle sugar on the skewers. Fresh meat is of course the best gift from nature, but the addition of extra sugar can control the direction of the Maillard reaction, and the caramelization of sugar itself (the fried sugar color in the braised pork) can also bring some extra flavor. This is an unconscious application of chemical knowledge by many barbecue stall owners.

Figure 2 Perfect grilling, charred skin and juicy internal meat fibers (Source: "A String of Life" Season 3)

Part 2

Continuation: Heat transfer and water retention, the moment of warmth between teeth

The Maillard reaction gives meat its initial flavor, but it is far from enough to make a perfect barbecue. In fact, although the charred skin of the skewer makes the barbecue burst with flavor the moment it enters the mouth, the moment when the teeth actually chew is the beginning of people's calorie intake.

Figure 3 Effect of heating on the particle size of protein assembly structures. a, simulated raw meat; b, after heating at 100℃ for 10 minutes; c, after heating at 100℃ for 30 minutes. Image source: Reference [5]

Fresh, tender and juicy is the highest praise for the internal meat fiber. If the Maillard reaction on the surface of the meat skewer is a chemical change at the small molecule level, then the formation of the taste inside the meat skewer depends more on the change of the three-dimensional structure of the protein and the retention of water. When the protein inside the meat skewer is heated, the original orderly assembled protein fiber structure will be destroyed - the so-called protein denaturation - so that the originally compact protein becomes soft and delicate, while releasing the locked water molecules to form gravy. From the changes in the protein assembly structure shown in Figure 3 [5], it can be seen that as the protein is heated, the large-sized aggregates are gradually disintegrated, and the proportion gradually decreases, and finally a smaller-sized protein assembly system is formed - thus obtaining a protein taste that is easier to chew.

Of course, the denaturation of proteins cannot be too much. As shown in Figure 4, before protein assembly, it is a loose structure without specific direction (a), after assembly, it is very tight (b), and after the assembly structure is partially destroyed, it becomes slightly loose (c). Corresponding to the taste of skewers, the texture of (b) that is not well roasted is hard and difficult to chew; (c) is roasted just right, with a fibrous chewy texture and soft and juicy; (a) often occurs when stewing meat, which is the so-called stewing too much, so that it melts in the mouth - this is not the taste required for barbecue.

Figure 4: Protein assembly and denaturation. a. Unassembled; b. Tightly assembled (raw meat); c. Partially destroyed (cooked meat) Image source: Reference [5]

The griller can of course achieve exquisite control over the taste of the internal meat. First, quickly form a melanin polymer layer of the Maillard reaction on the surface of the skewers, and then slowly heat it to denature the internal protein and produce gravy. Since melanin is a polymer, it can naturally effectively prevent the loss of water from the internal gravy and prevent the internal meat from becoming dry. The skewers are always juicy, with high water content and high specific heat of water, which can effectively prevent excessive denaturation of local meat proteins and ensure the ultimate taste of the skewers. In this process, the control of firepower is crucial, but the griller must also multitask - because when the internal meat produces juice, it is also the key to seasoning the skewers.

Part 3

Still at ease: barbecue and health, control the aroma of fire structure

From a chemical perspective, barbecue produces a lot of nitrogen-containing organic matter or aromatic compounds. They are the focus of barbecue flavor, but these substances are often linked to carcinogenicity. After all, dioxins and tar may be floating on the surface of the skewers. Moreover, in order to increase the flavor, many special barbecues are cooked with charcoal fire/fruit tree branches. The spices or organic matter carried by these natural plants naturally evaporate to the surface of the meat when burned, or directly physically adsorb to provide flavor, or participate in chemical reactions to give fragrance, making the skewers more special, but also bringing new health risks.

Figure 5 Barbecue produces a lot of nitrogen-containing organic matter, which may also be carcinogenic. Image source: Internet

According to scientific reports, a paper published in Nature in 2002 first proposed that acrylamide would appear in the Maillard reaction or in barbecue[6]. Acrylamide is a well-known potential carcinogen, so eating too much barbecue may increase the risk of cancer. But from another perspective, it is absurd to talk about toxicity without considering the dosage. The toxins ingested from an occasional barbecue may be far less than a cigarette of secondhand smoke.

In my mother's eyes, barbecue is a poison that affects health with carbon ash; in my eyes, barbecue is a fragrant antidote to depression and anxiety. Of course, although there is nothing that a barbecue can't solve, it seems more important to listen to my mother and not let her get hurt.

References:

[1] Maillard, LC. Action of amino acids on sugars. Formation of melanoidins in a methodical way. Comptes Rendus (in French). (1912), 154: 66–68.

[2] Hodge, JE. "Dehydrated Foods, Chemistry of Browning Reactions in Model Systems". Journal of Agricultural and Food Chemistry. 1953, 1 (15): 928–43.

[3] https://zh.wikipedia.org/wiki/%E7%BE%8E%E6%8B%89%E5%BE%B7%E5%8F%8D%E5%BA%94

[4] Van Boekel M. Kinetic aspects of the Maillard reaction: a critical review[J]. Food/Nahrung, 2001, 45(3): 150-159.

[5] Promeyrat A, Gatellier P, Lebret B, et al. Evaluation of protein aggregation in cooked meat[J]. Food Chemistry, 2010, 121(2): 412-417.

[6] Stadler RH, Blank I, Varga N, et al. Acrylamide from Maillard reaction products[J]. Nature, 2002, 419(6906): 449-450.

Source: Fanpu

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