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Fried Rice
一碗炒飯的奧秘
中國的美食文化一直都是讓歪果仁好奇的存在。在外國生活過的同學一定知道，國外的中餐廳最受歡迎的一個菜色就是炒飯。
“為什麼只有中餐廳才能做出如此入味的炒飯？”
“為什麼他們做出來的炒飯那麼漂亮？”
“傳說中的顛勺動作(Wok tossing)中包含哪些力學知識？”
帶著這些疑問，美國佐治亞理工學院的物理學家Hunting Ko和David Hu通過大量觀察與實驗，揭開了一碗完美炒飯的秘密——這個研究也許會讓你做的炒飯更好吃哦！
Wok tossing has long been suspected of causing the high shoulder injury rate among Chinese chefs.
一直以來，人們都懷疑中國廚師普遍存在的肩膀勞損是由於炒菜時的顛勺動作。
正文閱讀：
Fried rice is a classic dish in pretty much every Chinese restaurant, and the strenuous（adj. 費力的；奮發的） process of tossing the rice in a wok over high heat is key to producing the perfect final product. There's always chemistry involved in cooking, but there's also a fair amount of physics. Scientists at the Georgia Institute of Technology have devised a model for the kinematics（n. 運動學；動力學） of wok-tossing to explain how it produces fried rice that is nicely browned but not burnt. They described their work in a recent paper published in the Journal of the Royal Society: Interface.
中式炒飯幾乎是國外每一家中餐廳的必備經典菜式，而在高溫的鍋中不斷翻炒米飯，才是做出完美炒飯的關鍵。在這個烹飪過程中，大多數都屬於化學反應，不過也有很多物理知識涵蓋在裡面。美國喬治亞理工學院的科學家們最近就設計了一個“翻勺”的運動學模型，研究解釋瞭如何做出一份色澤出眾、不會燒焦的完美炒飯。他們在最近發表於《英國皇家學會雜誌》上的一篇論文中，詳細描述了他們的研究工作。
This work hails from David Hu's lab at Georgia Tech, known for investigating such diverse phenomena as the collective behavior（集體行為；集群行為） of fire ants, water striders, snakes, various climbing insects, mosquitos, the unique properties（屬性，性能）of cat tongues, and animal bodily functions like urination and defecation—including a 2019 Ig Nobel Prize-winning study on why wombats produce cubed poo. Hu and his graduate student, Hungtang Ko—also a co-author on a 2019 paper on the physics of how fire ants band together to build rafts—discovered they shared a common interest in the physics of cooking, particularly Chinese stir-fry.
這項研究來自佐治亞理工學院的大衛胡工作室，這個工作室以研究火螞蟻、水黽、蛇、爬行昆蟲、蚊子等動物的集體行為、貓咪舌頭的獨特屬性以及類似排尿排便系統——還包括獲得2019年搞笑諾貝爾獎的研究“為什麼袋熊會產出立方形的糞便”。胡教授和他的研究生柯同學——他也是2019年的一篇關於火螞蟻如何聚集在一起建造木筏的物理學論文的其中一個作者——他們發現兩人對烹飪中的物理學有共同的興趣，尤其是中式炒飯。
Hu and Ko chose to focus their investigation on fried rice (or "scattered golden rice"), a classic dish dating back some 1,500 years. According to the authors, tossing the ingredients（n. 材料；佐料）in the wok while stir-frying ensures that the dish is browned but not burned. Something about this cooking process creates the so-called "Maillard reaction": the chemical interaction of amino acids and carbohydrates subjected to high heat that is responsible for the browning of meats, for instance.
胡教授和柯同學兩人選擇將他們的研究重點放在炒飯（或稱為黃金蛋炒飯）上，這是一道擁有1500多年曆史的古老經典菜餚。根據研究者的說法，炒菜時不斷翻炒鍋中的材料，這樣可以確保做出來的飯是棕色的卻不會燒焦。這個烹飪過程產生了所謂的“美拉德反應”：氨基酸和碳水化合物在高溫下產生的化學反應，比如肉類變成褐色就是由這個反應導致的。
But woks are heavy, and the constant tossing can take its toll on Chinese chefs, some 64 percent of whom report chronic shoulder pain（慢性肩痛）, among other ailments. Hu and Ko thought that a better understanding of the underlying kinematics of the process might one day lead to fewer wok-related injuries for chefs.
但翻炒的鍋其實很重，不斷的顛勺翻鍋也會讓中國的廚師付出代價，大約有64%的中國廚師稱自己患有慢性肩痛。胡教授和柯同學認為，如果能夠更好地理解在這一過程的存在的潛在運動學，就有可能會在某天減少中國廚師因工作而受傷的情況。
In the summers of 2018 and 2019, Ko and Hu filmed five chefs from stir-fry restaurants in China cooking fried rice and then extracted frequency data from that footage. (They had to explain to patrons that the recording was for science and that they were not making a television show.) It typically takes about two minutes to prepare the dish, including sporadic wok-tossing—some 276 tossing cycles in all, each lasting about one-third of a second.
在2018年至2019年的夏天，胡教授和柯同學拍攝了五位中國餐館廚師的炒飯畫面，然後從視頻中提取頻率數據（他們必須向這些餐館老闆解釋，錄這些視頻是為了科學研究，並不是製作電視節目）。一般情況下，準備這道菜只需要兩分鐘左右的時間，包括偶爾的翻勺——總共約276次翻勺週期，每次只有大約三分之一秒。
拋接球的數學模型示意圖
Photo by Hungtang Ko and David Hu/Georgia Tech
Ko and Hu presented preliminary results of their experiments at a 2018 meeting of the American Physical Society's Division of Fluid Dynamics, publishing the complete analysis in this latest paper. They were able to model the wok's motion with just two variables, akin to a two-link pendulum, since chefs typically don't lift the wok off the stove, maintaining "a single sliding point of contact," they wrote. Their model predicted the trajectory of the rice based on projectile motion, using three metrics: the proportion of the rice being tossed, how high it was tossed, and its angular displacement.
胡教授和柯同學在2018年美國物理學會流體動力學分會的一次會議上展示了他們實驗的初步結果，並在最新的這篇論文中發表了完整的分析研究。他們寫道，他們能夠用兩個變量來模擬炒鍋的運動，就類似於一個雙擺，因為廚師通常不會把炒鍋直接從爐子上端起來，而是利用爐邊維持一個“滑動的接觸點”。他們的模型基於三個基礎指標：大米被拋擲的比例、被拋擲的高度和它的角位移。
The authors found two distinct（adj. 獨特的，截然不同的） stages of wok-tossing: pushing the wok forward and rotating it clockwise to catch rice as it falls; and pulling the wok back while rotating it counter-clockwise to toss the rice. Essentially, the wok executes two independent motions: side to side, and a see-sawing（蹺蹺板） motion where the left end moves in a clockwise circle and the right moves counterclockwise. "The key is using the stove rim as the fulcrum of the seesaw motion," the authors wrote. Also key: the two motions share the same frequency but are slightly out of phase.
研究人員發現，翻勺（此處指的是大翻勺，也就是將整個鍋裡的菜翻過去）有兩個不同的過程：將炒鍋向前推，順時針旋轉，以便在米飯落下時接住；然後把鍋拉回來，逆時針旋轉，把米飯翻過來。本質上，鍋是執行了兩個獨立的運動，從一邊到另一邊，一個蹺蹺板運動，其中左端以順時針方向運動，而右端以逆時針方向運動。在報告中研究人員這樣寫道：“關鍵是將爐邊作為蹺蹺板運動的支點。”而同樣關鍵的是，這兩個運動有相同的頻率，但又有輕微的不一致。
翻勺時的物理槓桿運動
Photo by Hungtang Ko and David Hu/Georgia Tech
Hu compared the effect to "flipping pancakes or juggling（n. 雜耍，手技雜耍） with rice." The trick is to ensure that the rice constantly leaves the wok, allowing it to cool a little, since the wok temperature can reach up to 1,200 degrees Celsius. That produces fried rice that is perfectly browned but not burned. Based on their analysis, Hu and Ko recommend that chefs increase both the frequency of motion when tossing fried rice in a wok and the "phase lag" （相位滯後）between the two distinct motions. This "may enable rice to jump further, and promote cooling and mixing."
胡教授將這種效應比作“翻煎餅或者翻炒飯”。這個過程的關鍵就是要確保米飯不斷地離開鍋，讓它在空中稍微冷卻一下，因為鍋裡的溫度甚至可以高達1200攝氏度。這種方法做出的炒飯是完美的褐色，但不會燒焦。根據他們的分析，胡教授和柯同學建議廚師在炒鍋裡翻炒時要增加動作的頻率，並且在兩種不同的動作之間增加“相位滯後”，這樣可能“使大米進一步翻滾，促進冷卻和混合。”
The mathematical model Hu and Ko developed isn't just a fun curiosity; it should also prove useful for industrial robotic designs. One goal for the authors is to develop a wearable exoskeleton（n. [昆] 外骨骼）or similar device to reduce the rate of shoulder injury among Chinese chefs. But there has been interest in automating cooking since the 1950s to perform such basic functions as cutting, boiling, frying, and pancake flipping—the latter task usually relying on reinforcement learning algorithms（n. [計][數] 算法；算法式）.
胡教授和柯同學建立的數學模型不僅僅是滿足了一個有趣的好奇心；這個模型也會對之後的工業機器人設計有所幫助。作者的一個目標是開發一種可穿戴的外骨骼或類似的設備，以減少中國廚師的肩膀勞損。不過早在20世紀50年代，人們就開始對自動化烹飪產生興趣了，自動化烹飪可以完成諸如切、煮、炸和翻炒等基本功能，而翻炒這一任務通常依賴於強化機器算法。
There have also been attempts to automate stir-frying fried rice in large batches, with limited success. Prior robotic designs have included a rotating drum（轉筒）to mix ingredients, and a see-sawing wok to flip ingredients, augmented with an automated spatula（n. 抹刀，小鏟）. These could mix ingredients via rotation or shaking but could not toss the rice and, thus, could not produce the ideal carbonated grains. "If there was an automated way of doing this, it could be very useful [for chefs]," said Hu.
當然，之前也有人嘗試過批量自動化地製作炒飯，但成效非常有限。之前的機器人設計包括一個旋轉滾筒來混合食材，一個蹺蹺板來翻轉食材，再加上一個自動的小鏟子。這些設備可以通過旋轉或者搖動來混合食材，卻不能攪拌大米，因此不能做出理想的美食。“如果有一種自動化的方式來做這件事，它（對廚師們）會非常有用，”胡教授這樣說。
實際上，這個研究並沒有那麼“無聊”
這些科學家們將研究目光
放在了一道平凡的菜色、一群普通的中國廚師身上
目標是解決廚師的肩膀勞損問題
和製作更長遠的人工智能美食
這樣潛心研究的科研精神
是不是可愛又可敬呢？
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