Why do bakers knead dough with ice water in summer?
― The water temperature is set by "subtracting" from room temperature
In bakeries, dough is mixed with water that has ice floating in it during summer, and lukewarm water in winter. The target isn't the water's temperature. It's keeping the finished dough at the same temperature all year round, regardless of season. To do that, bakers work backwards from the room temperature and the flour temperature to calculate the right water temperature.
It's a midsummer morning, still dark in a bakery kitchen. A baker measures water into a bowl and scoops in ice from the ice machine, crackling as it falls in.
After kneading, the baker sticks a thermometer into the dough, checks the reading, and nods. They jot the number down in a notebook before carrying the dough off to rest.
Come winter, the same baker is now adding hot water from a kettle instead. They're doing the exact opposite thing depending on the season, yet the thermometer reading is almost identical to summer's.
There are only two reasons
The yeast that makes dough rise is a living organism. Its working speed changes a lot with just a few degrees' difference. If the dough's temperature drifts, how much it rises and how it tastes will vary from day to day.
Dough temperature is decided by "adding up" the flour, the water, and the heat from kneading. Neither the flour's temperature nor the room temperature can be changed quickly. The only dial you can freely turn is the water.
In other words, ice water is a tool for pre-cancelling, with the water's coldness, the rise in temperature caused by summer heat. Let's look at each point in turn.
Yeast behaves completely differently depending on temperature
Bread rises because yeast in the dough breaks down sugar and releases carbon dioxide. This process speeds up as temperature rises. For many living organisms' chemical reactions, the rate is said to roughly double for every 10°C increase.
Faster sounds good, but it isn't. Inside the dough, at the same time as it's rising, the building blocks of flavor and aroma are slowly forming. If the temperature is too high, only the rising gets ahead. The dough stretches to its limit before the aroma has had time to develop, producing a sour smell or causing it to collapse when baked.
Conversely, if it's too low, the dough won't rise no matter how long you wait. So for many breads there's a target for the dough's temperature right after kneading finishes. This is called the "dough temperature after mixing," and for things like white bread, somewhere around 26–28°C is commonly used.
The reason a baker sticks a thermometer into the dough is to check this one number. If the temperature after mixing is consistent, the fermentation time afterward stays nearly the same every day. Keeping the temperature consistent is the shortcut to keeping the taste consistent.
Water is the only ingredient whose temperature is easy to change
So what decides the dough's temperature after mixing? Several things go into the dough, each at a different temperature.
- Flour: Stored in its bag in the kitchen, so it's roughly at room temperature.
- The bowl and surrounding air: Exchange heat with the dough while it's being kneaded.
- Kneading heat: Part of the force used to stretch the dough hundreds of times turns into heat. A mixer is said to raise it by a few degrees up to around 10°C.
- Water: The only ingredient you can freely set to whatever temperature you like, with ice or hot water.
If a summer kitchen is 30°C, then both the flour and the bowl are also 30°C. Add the kneading heat on top, and without any adjustment the dough will clearly exceed 30°C. To bring it back to the target 27°C, the only option is to make the water very cold. Try changing the room temperature with the dial in Figure 1.
Looking at Figure 1, for every 1°C rise in room temperature, the water must be cooled by 2°C. That's because the water alone is cancelling out the combined effect of flour and room temperature. Once the room temperature exceeds 32°C, the calculated water temperature drops below 0°C. That's why bakers in peak summer sometimes even keep the flour in the fridge.
The heat needed to warm the same 1 gram by 1°C is said to be more than double for water compared to wheat flour. That's why water, even in a smaller quantity than flour, can strongly pull the whole dough's temperature. Water makes an excellent dial.
How much the kneading heat raises the temperature depends on the type of machine, the kneading time, and the amount of dough. So bakers record the dough temperature after mixing every day. From the gap against their prediction, they work out the "rise" specific to their own kitchen. That's the number the baker was writing down in the notebook in the opening scene.
Summary
Bakers use ice water in summer not because they want to cool the water itself. It's because they want the finished dough's temperature to be the same every day. Since neither the flour nor the room temperature can be changed, they use the water temperature, which can be changed, to cancel out the seasonal difference all at once.
What the baker is matching isn't the water's temperature.
It's the temperature of the finished dough.
For how bread rising actually works, see "Why does bread rise?"; for how kneading force turns into heat, see "Why does rubbing your hands together make them warm?". For how ice absorbs heat as it melts, also see "Why does ice cool so much better than 0°C water?"
- Prepare 100 grams of flour and 70 grams of water, and measure each one's temperature with a cooking thermometer.
- Using the "temperature after mixing" formula in the collapsible section below, predict the mixed temperature and write it down on paper.
- Mix quickly in a bowl for about a minute, then immediately measure the temperature at the center of the dough and compare it with your prediction. Knead for another 5 minutes, then measure again.
The temperature should be a little higher after kneading. That rise is the "kneading heat" from your hands. Don't eat the flour raw.
Want to go deeper? ― Terms, formulas, and how they connect to the textbooksWe clearly mark which level each part belongs to, from junior-high science to university specialist courses
- Junior highCovered in junior-high science
- High schoolCovered in high-school "Basic Physics" / "Basic Biology"
- High school+High-school advanced content, or textbook sidebar material
- UniversityNot covered in high school — university specialist subjects (thermodynamics, food engineering, microbiology)
- ResearchNot yet taught as settled fact even at university — something researchers are still investigating
Junior highTerms: this phenomenon has names
- Dough temperature after mixing: The dough's temperature right after kneading finishes. One of the most important benchmarks in breadmaking.
- Mixing water: The water added to the dough. Adjusting its temperature is how you hit the target dough temperature after mixing.
- Specific heat: The amount of heat needed to raise 1 gram of a substance by 1°C. Water is known for being especially high among everyday substances.
Junior highHigh schoolCheck with the formula: what temperature is the mixing water in deep summer and deep winter?
There's a formula widely used on the breadmaking floor for deciding the mixing water's temperature. Let's calculate it for a deep-summer and a deep-winter kitchen.
| In symbols | T_water = 3 × (T_target − ΔT) − (T_room + T_flour) |
| In words | Water temperature = 3 × (target dough temperature after mixing − rise from kneading heat) − room temperature − flour temperature |
| Where it comes from | It's an empirical formula, solved for water, based on the idea that "the average of the three temperatures — water, flour, and surroundings (room) — becomes the dough's temperature before kneading." It's a simplified, floor-friendly version of the balance of heat exchange (conservation of heat). |
| Target dough temperature after mixing | 27℃ |
| Rise from machine kneading heat (example) | 6℃ |
| Deep-summer kitchen (room and flour both) | 30℃ |
| Deep-winter kitchen (room, flour) | Room 15℃, flour 12℃ |
| Specific heat of water | About 4.2 J/(g·℃) |
| Specific heat of wheat flour | Said to be about 1.7 J/(g·℃) |
| Required temperature before kneading | 27 − 6 ＝ 21 ℃ |
| Multiply by 3 | 21 × 3 ＝ 63 |
| Deep summer: room + flour | 30 ＋ 30 ＝ 60 |
| Deep-summer mixing water | 63 − 60 ＝ 3 ℃ |
| Deep winter: room + flour | 15 ＋ 12 ＝ 27 |
| Deep-winter mixing water | 63 − 27 ＝ 36 ℃ |
| Heat held per 1℃ in 70 g of water | 70 × 4.2 ＝ 294 J |
| Heat held per 1℃ in 100 g of flour | 100 × 1.7 ＝ 170 J |
| How many times more pull water has than flour | 294 ÷ 170 ≒ 1.7 times |
To make the same 27°C dough, summer needs 3°C ice water, while winter needs 36°C lukewarm water. The water temperature swings by more than 30°C with the season. This adjustment works because water, even in a smaller quantity than flour, can pull the temperature about 1.7 times as strongly as flour.
High schoolHigh school+The real heat balance, and what the "×3" means
High schoolWhen you mix things at different temperatures, the heat lost by the hotter side equals the heat gained by the colder side. This is called conservation of heat. With just water and flour, "mass of water × specific heat of water × (water temperature − mixed temperature) = mass of flour × specific heat of flour × (mixed temperature − flour temperature)" holds. The mixed temperature becomes an average weighted by heat capacity (mass × specific heat).
High school+The floor formula treats all three weights as equal, counting the bowl and surrounding air as one more "share." The real weights differ between flour and water, so it isn't a strictly theoretical formula. It's thought to persist because the amount by which the dough approaches room temperature while being kneaded gets absorbed into the "rise" figure through daily record-keeping. It's a formula that chose being correctable with the same daily procedure over strict accuracy.
UniversityKneading work and fermentation speed
Kneading heat is the work the mixer does on the dough, converted into heat through internal friction. In food engineering, there's an approach to managing dough condition based on the amount of work put into kneading. Meanwhile, how fermentation speed changes with temperature is expressed through the Arrhenius equation, which links reaction rate and temperature, and the temperature coefficient (Q10), which expresses the rate ratio per 10°C. The fact that shifting the dough temperature after mixing by just 1–2°C visibly changes fermentation time is due to this exponential dependence.
📖 For the derivation of the formula and further reading: Arrhenius equation (Wikipedia, Japanese) ／ Heat capacity (Wikipedia, Japanese)
ResearchWhat isn't fully understood yet
- Can kneading heat be predicted accurately in advance? How heat is generated varies greatly with the dough's moisture, the type of flour, and the kneading method. Research continues into predicting dough temperature rise from a mixer's power consumption.
- Why does fermenting at a low temperature for a long time improve aroma? Overnight fermentation in the fridge is a popular method. Which aroma compounds increase through which reactions isn't fully known yet.
- How much does yeast's response to temperature vary by strain? Yeasts with different traits, such as strains that are robust in cold dough, are being selected. Where in the genes that difference comes from is still being researched.
In other words, the content of this article too is "the explanation as currently understood." The floor formula arose from experience before the science did, with theory catching up afterward.
Connections to the textbooks (by level)
| Level | Subject/unit | Where in this article |
|---|---|---|
| Junior high | Science (how heat travels, energy conversion) | Kneading force turning into heat, flour and water temperatures mixing |
| High school | Basic Physics (conservation of heat, specific heat), Basic Biology (enzymes and respiration) | The heat-balance formula, how yeast activity relates to temperature |
| High school+ | Physics (weighted average via heat capacity) | Why the floor's "×3" formula is a simplification |
| University | Thermodynamics, food engineering, microbiology | Kneading work and temperature rise, the Arrhenius equation and temperature coefficient |
| Research | Breadmaking science, fermentation science | Predicting kneading heat, aroma from low-temperature fermentation, differences between yeast strains |
| ― | Connection to daily life | Why water temperature is changed with the season when baking bread at home |
- Koji Taketani, Atarashii Seipan Kiso Chishiki (New Basic Knowledge of Breadmaking), Pan News Sha (パンニュース社)
- Seiichi Yoshino, Pan "Kotsu" no Kagaku (The Science of Bread "Tricks"), Shibata Shoten (柴田書店)
- National Astronomical Observatory of Japan (ed.), Rika Nenpyo (Chronological Scientific Tables), Maruzen Publishing (丸善出版) (specific heat of water)
- Specific heat capacity (Wikipedia, Japanese)
- Fermentation (Wikipedia, Japanese)
※This article is a general-audience science explainer. The figures given are rough estimates meant to help illustrate the mechanism. The dough temperature after mixing and the rise from kneading will vary by type of bread, machine, and recipe.