A warm place溫暖的地方
The yeast works fast. White dots of gas stream into the bubbles, and the dough is nearly twice as big in an hour.
酵母做得很快。白色的氣體小點不斷飄進氣泡，一個小時麵糰就快要兩倍大。
How Things Work · Unit 5 · Lesson 18 · 萬物原理 單元五 第十八課
Why Does Bread Rise?麵包為什麼會膨脹？
The holes in bread and steamed buns are made by yeast, a tiny living thing that eats sugar and gives off gas. Cut a ball of dough in half in 3D, watch the bubbles grow, try it warm, cold, and without yeast, then bake it.
麵包和饅頭裡的小洞是酵母做出來的。酵母是活的小生物，吃糖、吐出氣體。在 3D 裡把麵糰切開一半，看氣泡長大；試試溫暖的地方、冰箱裡、沒有酵母，最後送去烤。
Big idea · 一句話看懂
Yeast is a tiny living thing. In dough it eats sugar and gives off carbon dioxide gas. Stretchy gluten in the dough traps the gas in thousands of little bubbles, and the growing bubbles push the dough up. Baking or steaming makes the gas swell once more and then sets the dough, so the holes stay.
酵母是活的小生物。它在麵糰裡吃糖，吐出二氧化碳。麵糰裡有彈性的麵筋把氣體包成成千上萬個小氣泡，氣泡越長越大，就把麵糰撐高。烤或蒸的時候，氣體受熱再脹大一次，接著麵糰定型，小洞就留了下來。
3D Model · 3D 模型
Inside a Ball of Dough 麵糰的裡面
Drag to turn the view, and scroll or pinch to zoom. The dough is cut in half so you can see inside. Orange specks are yeast, white dots are gas, and the round holes are bubbles. Let the time run, or drag the time slider. Make it warmer or colder, switch the yeast off, and press “Bake it” when the dough is ready.
拖曳可以旋轉視角，滾輪或雙指可以縮放。麵糰被切開一半，讓你看到裡面。橘色的小點是酵母，白色小點是氣體，圓圓的洞是氣泡。讓時間自己走，或拉時間滑桿；把溫度調高調低、把酵母關掉，等麵糰發好了再按「送去烤」。
A ball of dough cut in half; yeast and bubbles drawn far bigger and far fewer than real · 切開一半的麵糰；酵母和氣泡畫得比真的大非常多、也少非常多
Drag to turn · 拖曳旋轉 Scroll or pinch to zoom · 滾輪／雙指縮放
This 3D model needs WebGL, which this browser does not support. The reading and the cards below still explain everything.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的課文與卡片一樣能看懂。
- Orange specks: yeast
橘色小點：酵母 - White dots: carbon dioxide gas on its way to a bubble
白色小點：正要飄進氣泡的二氧化碳 - Round holes: gas bubbles
圓圓的洞：氣泡 - Cream color: the dough, held together by stretchy gluten
米白色：麵糰，靠有彈性的麵筋連在一起
A teaching model, not a recipe. The speeds and sizes come from a simple formula chosen to show the pattern (warm is fast, cold is slow, no yeast means no rise); real dough depends on the flour, the yeast, and the recipe. One second here stands for about six minutes. Real yeast cells are far too small to see without a microscope, and real dough holds more of them than anyone could count.
這是教學用的模型，不是食譜。速度和大小來自一條簡單的算式，只是為了呈現趨勢（溫暖就快、冷就慢、沒有酵母就不會發）；真正的麵糰要看麵粉、酵母和做法。這裡的 1 秒大約代表 6 分鐘。真正的酵母小到要用顯微鏡才看得見，麵糰裡的酵母多到數不清。
Model drawn by My Culture Connect as a teaching diagram. What yeast does in dough follows Wikipedia, “Baker's yeast”. · 模型由人師教育協會自繪示意；酵母在麵糰裡做的事，依維基百科「Baker's yeast」條目。
Reading · 英文閱讀
18
Unit 18: Why Does Bread Rise?
Tear open a steamed bun or a slice of toast and look closely. It is full of tiny holes, like a sponge. A dumpling wrapper is made from flour and water too, but it is flat and thin, with no holes at all. So who put the holes in the bread?
把一顆饅頭或一片吐司撕開，仔細看。裡面滿滿都是小洞，像海綿一樣。水餃皮也是麵粉和水做的，卻又扁又薄，一個洞也沒有。那麼，麵包裡的洞是誰做的？
The answer is yeast. Yeast is not a chemical. It is a tiny living thing, a kind of fungus, and each one is a single cell far too small to see. The dry yeast in a packet looks like sand because the yeast is asleep. Give it warm water and a little food, and it wakes up.
答案是酵母。酵母不是化學藥品，而是活的小生物，是一種真菌；每一個都只有一個細胞，小到看不見。小包裝裡的乾酵母看起來像沙子，因為酵母睡著了。給它溫水和一點食物，它就醒過來。
Yeast loves sugar, and there is sugar in dough. As the yeast eats, it gives off a gas called carbon dioxide, the same gas that makes the bubbles in soda. It also makes a little alcohol. Countless yeast cells are doing this all through the dough at the same time.
酵母愛吃糖，而麵糰裡就有糖。酵母一邊吃，一邊吐出一種氣體，叫二氧化碳，就是汽水裡冒泡泡的那種氣體。它也會做出一點點酒精。整塊麵糰裡，數不清的酵母同時都在做這件事。
Why doesn't the gas just float away? When you mix flour with water and knead it, a stretchy net called gluten forms inside the dough. The gluten traps the gas in little bubbles, like thousands of tiny balloons. As the balloons fill, the whole dough swells. In a warm place the yeast works fast. In the refrigerator it works very slowly.
氣體為什麼不會直接飄走？麵粉加水再揉一揉，麵糰裡就會形成一張有彈性的網，叫做麵筋。麵筋把氣體包在小氣泡裡，像成千上萬個小氣球。氣球越吹越大，整塊麵糰就鼓起來。在溫暖的地方，酵母做得快；在冰箱裡，它做得非常慢。
Then comes the heat. In a hot oven or a steamer, the gas in every bubble swells once more, and the dough gets even bigger. Soon the dough sets firm, the heat stops the yeast, and the alcohol evaporates. The bubbles cannot shrink back. They stay as the soft holes you see in bread and steamed buns.
接著是加熱。在很熱的烤箱或蒸籠裡，每個氣泡裡的氣體又脹大一次，麵糰變得更大。很快地，麵糰定型了，高溫讓酵母停下來，酒精也蒸發了。氣泡縮不回去，就留下來變成你在麵包和饅頭裡看到的鬆軟小洞。
People have baked bread for thousands of years without knowing why it rose. In 1680, Anton van Leeuwenhoek saw yeast through a microscope for the first time. Almost two hundred years later, Louis Pasteur showed that living yeast does the work. So the next time you eat a steamed bun, say thank you to all those tiny helpers.
人類做麵包做了幾千年，卻一直不知道它為什麼會膨脹。1680 年，雷文霍克第一次在顯微鏡下看到酵母。將近兩百年後，巴斯德證明這件事是活的酵母做的。下次吃饅頭的時候，記得謝謝那些數不清的小幫手。
Read aloud · 課文朗讀
Questions · 閱讀理解
What is yeast?
A tiny living thing, a kind of fungus. Each one is a single cell, far too small to see.
What does yeast give off when it eats sugar, and what keeps it inside the dough?
It gives off carbon dioxide gas (and a little alcohol). Stretchy gluten traps the gas in little bubbles.
What happens to the bubbles when the dough is baked or steamed?
The gas swells once more, and then the dough sets firm, so the bubbles stay as holes.
Words & Phrases · 生字及片語
yeast(n.)酵母Add a spoonful of yeast to the flour.在麵粉裡加一匙酵母。dough(n.)麵糰Cover the dough and wait for an hour.把麵糰蓋起來，等一個小時。rise(v.)（麵糰）發起來；上升The dough will rise faster in a warm place.麵糰在溫暖的地方發得比較快。bubble(n.)氣泡Soda is full of tiny bubbles.汽水裡有很多小氣泡。knead(v.)揉（麵）Knead the dough until it is smooth.把麵糰揉到光滑。stretchy(adj.)有彈性的A rubber band is stretchy.橡皮筋很有彈性。trap(v.)困住；包住A thick coat traps warm air.厚外套會把暖空氣包住。swell(v.)膨脹The balloon swelled as I blew into it.我一吹，氣球就膨脹起來。
Quick Check · 小測驗
1. What is yeast?
2. What gas does yeast give off in dough?
3. What traps the gas inside the dough?
4. Where does dough rise fastest?
5. Why are there holes in baked bread?
Try It in the Model · 在模型裡試試
Four balls of dough 四塊麵糰
Try baking the dough with no yeast, too. With no gas inside, the heat has nothing to swell.
也試試把沒有酵母的麵糰拿去烤：裡面沒有氣體，加熱也沒有東西可以脹大。
In the refrigerator冰箱裡
The same dough, kept cold. The yeast is still alive, but it works so slowly that the dough has hardly grown.
同樣的麵糰，放在冷的地方。酵母還活著，但是做得很慢，麵糰幾乎沒長大。
No yeast沒有酵母
Flour and water alone. Nothing makes gas, so no bubbles grow, however long you wait.
只有麵粉和水。沒有東西製造氣體，等再久，氣泡也不會長大。
Into the oven送進烤箱
The risen dough meets the heat. Every bubble swells once more, the crust turns golden, and the holes are fixed in place.
發好的麵糰遇到高溫。每個氣泡再脹大一次，外皮變成金黃色，小洞就固定下來了。
Yeast by the Numbers · 酵母的數字
Small helpers, long history 小小的幫手，長長的歷史
From a steamed cake written about seventeen centuries ago to the yeast in your kitchen.
從一千七百多年前文章裡的蒸餅，到你家廚房裡的酵母。
5–10micrometers · 微米
The width of one yeast cell. A micrometer is one thousandth of a millimeter.一個酵母細胞的大小。1 微米是千分之一毫米。
2things yeast makes · 種產物
Yeast turns sugar into carbon dioxide gas and alcohol. The alcohol evaporates during baking.酵母把糖變成二氧化碳和酒精；酒精在烘烤時就蒸發了。
40–45°Cwarm water · 溫水
Bakers often wake up dry yeast in warm water at about this temperature, with a little sugar.烘焙的人常用大約這個溫度的溫水，加一點糖，把乾酵母叫醒。
About 300CE · 西元 300 年左右
The Chinese writer Shu Xi wrote about steamed cakes, an early relative of today's steamed buns.西晉的束皙在文章裡寫到「蒸餅」，是今天饅頭的老前輩。
1680first seen · 第一次被看見
Anton van Leeuwenhoek saw yeast through a microscope, but did not know it was alive.雷文霍克在顯微鏡下看到酵母，但當時不知道它是活的。
1857alive! · 它是活的！
Louis Pasteur studied yeast and showed that living yeast, not a chemical, does the fermenting.巴斯德研究酵母，證明發酵是活的酵母做的，不是化學藥品。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Dough rises because the flour soaks up water and swells.麵糰變大，是因為麵粉吸了水脹起來。
✓ Fact · 事實Dough rises because yeast fills it with gas. Without yeast, the same flour and water stay flat.麵糰變大是因為酵母讓它充滿氣體。沒有酵母，同樣的麵粉和水還是扁的。
✗ Myth · 迷思Yeast is a chemical powder.酵母是一種化學粉末。
✓ Fact · 事實Yeast is alive. It is a tiny fungus that sleeps when it is dry and wakes up in warm water.酵母是活的。它是很小的真菌，乾的時候睡著，碰到溫水就醒過來。
✗ Myth · 迷思Bread is full of alcohol, because yeast makes alcohol.酵母會做出酒精，所以麵包裡都是酒精。
✓ Fact · 事實Yeast makes only a little alcohol in dough, and it evaporates during baking.酵母在麵糰裡只做出一點點酒精，而且在烘烤時就蒸發了。
✗ Myth · 迷思Everything soft and fluffy is made with yeast.鬆鬆軟軟的東西都是用酵母做的。
✓ Fact · 事實Many cakes and cookies use baking powder or baking soda instead. These make gas by a chemical reaction, with no living thing at all.很多蛋糕和餅乾用的是泡打粉或小蘇打，靠化學反應產生氣體，裡面沒有任何活的東西。
Remember It · 記憶口訣
Bread in a sentence 一句話記住麵包
Yeast is alive酵母是活的
A tiny fungus that eats, makes gas, and can fall asleep.
一種很小的真菌，會吃東西、會吐氣，也會睡著。
Sugar in, gas out吃進糖，吐出氣
Yeast eats sugar and gives off carbon dioxide.
酵母吃糖，吐出二氧化碳。
Gluten is the balloon麵筋是氣球
Stretchy gluten traps the gas so the dough can swell.
有彈性的麵筋把氣體包住，麵糰才鼓得起來。
Warm is fast, heat sets it溫暖發得快，高溫定型
Warmth speeds the yeast up. The heat of baking fixes the holes in place.
溫暖讓酵母變快；烘烤的高溫把小洞固定下來。
Safety First · 安全提醒
Before you try anything 動手之前先讀
- Ovens, steamers, and hot water are for adults to handle. Stand back when the oven door or the steamer lid is opened.烤箱、蒸籠和熱水要由大人操作。打開烤箱門或蒸籠蓋的時候要站遠一點。
- Do not eat raw dough. Uncooked flour can carry germs that make you sick.不要吃生的麵糰。沒煮過的麵粉可能帶有讓人生病的病菌。
- Wash your hands with soap before and after you touch dough.碰麵糰之前和之後，都要用肥皂洗手。
- If you are allergic to wheat or cannot eat gluten, do not touch the flour. Help by timing and writing notes instead.對小麥過敏或不能吃麩質（麵筋）的同學不要碰麵粉，可以改當計時和記錄的人。
- In the balloon activity, never screw a cap onto the bottle. The gas needs somewhere to go.做氣球活動時，絕對不要把瓶蓋鎖上，氣體要有地方去。
Classroom Activity 1 · 課堂活動一
Blow Up a Balloon with Yeast 讓酵母吹氣球
You need · 準備材料
- Two small plastic bottles and two balloons兩個小寶特瓶和兩個氣球
- Dry yeast, sugar, warm water, and cold water乾酵母、糖、溫水和冷水
Steps · 步驟
- Put a spoonful of yeast and a spoonful of sugar into each bottle.每個瓶子各放一匙酵母和一匙糖。
- Ask an adult to add warm water to one bottle and cold water to the other, about a quarter full.請大人在一個瓶子裡加溫水、另一個加冷水，大約四分之一滿。
- Stretch a balloon over the mouth of each bottle and swirl gently.在兩個瓶口各套上一個氣球，輕輕搖一搖。
- Check every ten minutes for half an hour. Which balloon grows faster? What is filling it?每十分鐘看一次，看半小時。哪個氣球長得快？是什麼把它撐起來的？
The water should feel warm on your wrist, not hot. The gas in the balloon is the same gas that makes holes in bread.
水滴在手腕上要覺得溫溫的，不能燙。氣球裡的氣體，就是在麵包裡做出小洞的那種氣體。
Classroom Activity 2 · 課堂活動二
Bread Detective 麵包小偵探
You need · 準備材料
- A steamed bun, a slice of bread, and a cooked dumpling wrapper or a flour tortilla一顆饅頭、一片吐司，和一張煮熟的水餃皮或蛋餅皮
- A magnifying glass, a notebook, and a pencil放大鏡、筆記本和鉛筆
Steps · 步驟
- Tear each one open and look at the inside with the magnifying glass.把每一樣都撕開或掰開，用放大鏡看裡面。
- Draw what you see. Which one has the biggest holes? Which has none?把看到的畫下來。哪一個的洞最大？哪一個沒有洞？
- Press each one gently with a finger. Which springs back?用手指輕輕壓一壓。哪一個會彈回來？
- Read the ingredients on the packages. Which ones list yeast?讀一讀包裝上的成分。哪幾樣有寫酵母？
The holes are the bubbles that the yeast blew up, fixed in place by the heat.
那些洞就是酵母吹大的氣泡，被高溫固定下來了。
Sources · 資料出處
Facts and numbers on this page were checked against these sources (October 2026). · 本頁的事實與數字依下列資料查證（2026 年 10 月）。
- Baker's yeast makes bread rise by turning the sugars in dough into carbon dioxide and ethanol麵包酵母把麵糰裡的糖變成二氧化碳和乙醇，讓麵包膨脹Wikipedia, “Baker's yeast” ↗
- Baker's yeast is a single-celled fungus; its cells are 5–10 micrometers across麵包酵母是單細胞的真菌，細胞大小 5–10 微米Wikipedia, “Saccharomyces cerevisiae” ↗
- Gluten is the elastic network of wheat proteins that gives dough its stretch and helps it rise and keep its shape麵筋是小麥蛋白質形成的彈性網，讓麵糰有彈性、發得起來並保持形狀Wikipedia, “Gluten” ↗
- Warm temperatures speed the yeast up and cold slows it down; dry yeast is woken in warm water (about 40–45°C) with a little sugar; a well-risen dough swells again in the oven溫暖讓酵母變快、低溫讓它變慢；乾酵母用溫水（約 40–45°C）加一點糖叫醒；發得好的麵糰進烤箱會再脹大Wikipedia, “Proofing (baking technique)” ↗
- Leeuwenhoek first saw yeast under a microscope in 1680; Pasteur showed that living yeast carries out fermentation; the ethanol evaporates during baking雷文霍克 1680 年第一次在顯微鏡下看到酵母；巴斯德證明發酵是活的酵母進行的；乙醇在烘烤時蒸發Wikipedia, “Yeast” ↗
- Shu Xi wrote about steamed cakes (蒸餅) around 300 CE束皙約在西元 300 年的〈湯餅賦〉寫到蒸餅Wikipedia, “Mantou” ↗
- Chemical leaveners such as baking powder and baking soda release gas by reaction, used where a long fermentation is not wanted泡打粉、小蘇打等化學膨鬆劑靠反應放出氣體，用在不適合長時間發酵的地方Wikipedia, “Leavening agent” ↗
- Do not eat raw dough: uncooked flour can contain germs不要吃生麵糰：沒煮過的麵粉可能帶有病菌U.S. Centers for Disease Control and Prevention ↗