7.2 Water: boiling points and dispersions

Water carries heat to food on the range top. Two things about it are worth seeing for yourself: what water looks like at different temperatures, and how things mixed into water change it.

Temperature words

Start by checking your thermometer in boiling water. Then heat a pan of water and watch it change. These terms name what you see:

• Lukewarm: 30 to 37°C.
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• Simmering: 85 to 99°C. Look at the surface of the water to learn what a simmer looks like.
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• Boiling: 100°C. A slow boil and a rapid boil (also called a rolling or fast boil) look different on the surface.
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To change between the two scales, use these formulas: °C = (°F − 32) ÷ 1.8, and °F = (°C × 1.8) + 32.

Hotter or cooler than a boiling pan

Some pans hold water below boiling, and some push it above.

• Double boiler. Water in the top pan sits over boiling water in the bottom pan, and the bottom water should not touch the top pan. The top water reaches 190 to 198°F at most. Think about whether the top water would boil if the bottom water touched it, and what jobs suit this gentle heat.
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• Steamer. A thermometer in a cup of water set in the top of a steamer reaches 91°C. Compare how fast food cooks in a steamer and in a saucepan.
• Pressure saucepan. Pressure raises the boiling point: water boils at 109°C at 5 pounds of pressure, 240°F at 10 pounds, and 121°C at 15 pounds. Think about how this changes cooking time compared with a normal saucepan.
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Dispersions

The questions to answer from your results:

• What kind of dispersion does each added substance make, and how does it change the boiling point?
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• Why might two substances in the same kind of dispersion change the boiling point by different amounts?
• What would each one do to the freezing point?
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