The science behind cooking

  The soul of frying lies in temperature and speed. Cantonese chefs pay attention to wok qi (also written as wok qi), which is simply to make food emit a burnt aroma under high temperature and fierce fire. To fry the vegetables out of the gas, firstly, the stove must be fierce to reach the temperature where the gas appears; secondly, the stir-frying time must be short enough so that the moisture in the ingredients will not be fried out, which will affect the gas. In Cantonese cuisine, the dish that best reflects the gas is dry fried Niuhe. It takes less than 2 minutes for a skilled chef to complete the process from putting the beef into the frying pan to serving the dishes. While the diners are full of praise, they don’t know that the secret of Jiao Xiang’s fullness is not the secret sauce, but the Maillard reaction.
  In 1912, the French chemist Maillard discovered that amino acids and sugars would undergo a series of browning reactions at high temperatures and produce thousands of aromatic molecules. This reaction was named “Maillard reaction”. After Maillard, scientists discovered that when the temperature is 140-170℃ (the temperature range in the pot when making Chinese stir-fry dishes), the efficiency of the Maillard reaction is the highest. With the help of Maillard reaction, the amino acids and reducing sugars in beef, rice noodles, onions and chives react quickly to produce a variety of attractive aromas. In fact, in addition to stir-fried dishes, the scorched aromas of roast chicken, roast duck, fried steak, pancakes, fritters, coffee and chocolate also mainly come from the magical Maillard reaction.
  Oil is another important participant in this cooking method of “stir-frying”. The boiling points of common edible oils are above 200°C, and the boiling points of peanut oil and rapeseed oil even reach 335°C. The oil can quickly heat the food at a higher temperature to avoid oxidation of the food due to long-time cooking, thereby preserving the nutrition and taste of the food. In addition, nutrient elements such as vitamin A need to be dissolved in oil to be absorbed by the body. However, although the working temperature of edible oil is very high, its specific heat capacity is generally less than 1/2 of water, which means that the same volume of oil can store less than 1/2 of water. Too many ingredients will quickly cool the oil in the pot, and it is difficult to maintain the temperature range required for Maillard reaction. Therefore, restaurant chefs use wide oils (many oils) when cooking in order to maintain the oil temperature.


  ”The batter was fried until golden, and the children next door were crying” is a popular sentence in recent years. From deep-fried dough sticks (carbohydrates) to croquettes (proteins), almost any ingredient can be deep-fried. Some businesses in Hokkaido, Japan even sell fried maple leaves as a local specialty tourist food to tourists. If you want to use one word to summarize the charm of fried food, it is mostly “crispy.”
  A piece of breadcrumbs-wrapped chicken wings was placed in a 160°C oil pan. There was a loud noise in the pan, and countless bubbles rose from the surface of the chicken wings with crackling noises. The principle of frying is to quickly dehydrate and heat the ingredients, and the rising bubbles are the result of the rapid expansion, vaporization and escape of the water contained in the bread crumbs and chicken skin at high temperatures. In the process of thermal expansion of water, small cavities are formed on the surface of the food by air bubbles. These cavities harden because of the continuous reduction of water before they can return to their original state. As a result, the outer layer of the fried food becomes an enlarged hard shell composed of many cavities. This is the secret of the crispy taste of the outer layer of the fried food. However, while improving the taste, the cavity also becomes a “small warehouse” for storing grease. When we eat fried food, we also eat a lot of fat together.

  To get a crispy crust, the key is to control the gluten content in the flour. Gluten is the protein in flour. Because the protein network structure easily absorbs water and oil, the more protein in the batter, the wetter and greasy the fried crust. If you want to fry a crispy crust, you must choose low-gluten flour (cake flour), or mix a certain amount of starch (no protein) in all-gluten flour (steamed bun flour, bun flour).


  When it comes to grilling, charcoal grilling is indispensable. Although the burning charcoal does not have an open flame, it can heat the mutton and seafood to “sizzle”, which is the effect of heat radiation. To understand this heating method, think of the sun. There is a distance of 150 million kilometers between the sun and the earth. There is no air that can transfer heat, but we can still feel the heat that the sun radiates to us.
  The heat source for roasting is not necessarily charcoal. The famous “food writer” Liang Shiqiu described the iron pot eggs he had eaten in a Henan restaurant in Beiping called Hou Defu in “Ya She Talks about Eating”: “Hou Defu’s iron pot eggs are grilled. So unique.” To make an iron pot egg, you must first prepare a thick iron pot with a small bottom, a large mouth, and a height. Then mix the whipped egg with the oil and salt seasoning, then mix in a small amount of minced meat and peas, and pour it over to heat. On the iron pan, bake with the simmering tape until the egg rises to the mouth of the pot and is browned, then you can pick it up and serve it on the table. The iron pan used in iron pan eggs is a cast iron pan, and its cooking principle is closer to roasting. Forged woks have a thin body and rapid heat conduction; while cast iron pans are made with a casting process, which is difficult to make thin, so they are generally thicker. However, it is precisely because of its thickness that the cast iron pan can store more heat than the wok pan, so that the food is heated mainly by heat radiation (roasting).
  Zhizi barbecue is one of the Mongolians’ dietary styles, and Zhizi may best play the broiling ability of cast iron. Zhizi is a large round roasting pan made of cast iron. The large Zhizi can cover almost the entire dining table. The broil made of thick cast iron absorbs a lot of heat from the charcoal fire, and the mutton can be cooked in a short time, keeping the tenderness of the mutton to the greatest extent. At the same time, the mutton releases a rich fragrance after experiencing Maillard reaction, which makes the teeth and cheeks fresh.


  On Dongchenggen South Street, near the People’s Park of Chengdu, there is a 爿hoe flower shop. Hoof flower is the Chengdu dialect, referring to stewed trotters. The hoof flowers here are very soft and waxy, but one can be picked up completely with chopsticks. Pig’s feet contain many connective tissues that connect muscle fibers. It is logically one of the strongest parts of a pig’s body. Then, how come the pig’s feet are stewed so softly?
  Stew provides a hot and humid environment for food, which can effectively decompose strong connective tissue (mainly collagen). A single collagen fiber is composed of three strands of gelatin. The gelatin is broken up during the stewing process, which disintegrates the collagen structure and makes the originally difficult-to-chew pig’s feet soft and delicious. During the stewing process, many gelatin molecules dissolve into the soup. After the soup cools, these gelatins reconnect together, allowing the soup to solidify into aspic.
  Unlike many people think, stewing does not increase the moisture in the meat. The quality of the stewed meat will be reduced by 20%-40% due to shrinkage. These lost substances are mainly the water in the meat. The water in the meat is mainly stored in the muscle fibers. During the stewing process, the muscle fibers begin to contract and the water in them escapes. To keep the meat juicy and soft, it is necessary to reduce the water loss of muscle fibers. For this reason, some people came up with a long-term low-temperature slow-cooking method: they sealed the meat and seasonings with a silicone bag, put them in a constant temperature water bath, controlled the temperature at 50~80℃, and the cooking time at 2-48 hours. . The meat cooked in this way not only retains a lot of gravy, but also has a much softer taste than ordinary stewed meat.

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