Kitchen Science
Discover why bread rises, onions make you cry, and small cooking choices make a big difference.
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Questions with solutions-
1. Velg riktig svar.
What makes the dough expand?
Bread dough containing yeast grows larger while it rests in a warm place.
- Yeast pulls air into the dough from the room.
- Yeast releases gas that becomes trapped in the dough.
- Yeast heats the water in the dough until it becomes steam.
Think about what forms the small holes inside baked bread.
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- Yeast releases gas that becomes trapped in the dough.
Yeast feeds on sugars and produces carbon dioxide. The dough stretches around the growing gas bubbles.
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2. Velg riktig svar.
What causes the kernel to burst?
A popcorn kernel contains a little water inside a hard outer shell. When heated, it suddenly pops.
- The shell shrinks and squeezes the dry starch outward.
- The starch melts and slowly leaks through the shell.
- Steam builds pressure until the shell breaks.
The hard shell prevents something inside from escaping.
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- Steam builds pressure until the shell breaks.
When the shell breaks, the pressure drops suddenly, allowing the hot, softened starch to expand rapidly.
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3. Velg riktig svar.
What usually causes this reaction?
Your eyes begin to water while someone across the counter chops a fresh onion.
- An irritating substance travels through the air to your eyes.
- Solid onion particles fly directly into your eyes.
- The onion's smell removes moisture from your eyes.
You do not need to touch the onion for your eyes to react.
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- An irritating substance travels through the air to your eyes.
Cutting brings chemicals and enzymes from damaged cells together, creating a substance that irritates the eyes.
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4. Velg riktig svar.
Why does the oil sit on top?
You pour olive oil and water into a glass. After they settle, the oil forms the upper layer.
- Oil is thicker, so it cannot sink through water.
- Oil is less dense than water.
- Water always pushes oil upward, regardless of its density.
Compare the mass of equal amounts of the two liquids.
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- Oil is less dense than water.
Density means mass for a given volume. A spoonful of oil has less mass than an equal volume of water.
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5. Velg riktig svar.
How do these drops form?
You lift a metal lid from a pot of hot soup. Water drops cover the cooler underside of the lid.
- Water vapor cools and turns back into liquid.
- Liquid water passes through tiny holes in the metal.
- Water vapor gathers into drops but remains a gas.
Consider what happens when warm water vapor meets a cooler surface.
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- Water vapor cools and turns back into liquid.
This change is called condensation. It also explains the drops that form outside a cold drinking glass.
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6. Velg riktig svar.
What mainly causes this change?
An egg white changes from clear and runny to white and firm as it cooks.
- Nearly all the water evaporates from the egg white.
- Unchanged proteins are simply pressed closer together.
- Heat changes the proteins, allowing them to form a network.
The important change happens to the egg's proteins, not just its water.
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- Heat changes the proteins, allowing them to form a network.
The protein changes are not easily reversed, so cooling a cooked egg does not make it raw again.
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7. Velg riktig svar.
What does turning the heat up mainly do?
Pasta is cooking in an uncovered pot, and the water is already boiling.
- It raises the water temperature far above its boiling point.
- It produces more steam, with little change in water temperature.
- It lowers the water temperature by producing more bubbles.
More bubbling does not necessarily mean hotter water.
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- It produces more steam, with little change in water temperature.
Once water boils, extra heat mainly turns more water into steam. A steady boil is usually enough to cook pasta.
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8. Velg riktig svar.
How does the egg yolk help?
Oil and water normally separate. In mayonnaise, egg yolk helps them remain mixed after whisking.
- It helps small oil droplets stay spread through the water.
- It changes the oil into water, creating a single liquid.
- It makes the oil heavy enough to settle at the bottom.
The oil remains oil, even when the mixture looks smooth.
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- It helps small oil droplets stay spread through the water.
Egg yolk contains emulsifiers, substances that help stop separate oil droplets from joining back together.
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9. Velg riktig svar.
Why does the sauce thicken?
You stir a mixture of cornstarch and cold water into a hot sauce. The sauce soon becomes thicker.
- Most of the water must boil away before thickening begins.
- The starch turns into sugar, making the sauce sticky.
- Starch particles absorb water and swell as they heat.
The sauce can thicken before much water has evaporated.
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- Starch particles absorb water and swell as they heat.
Mixing cornstarch with cold water first separates the particles and helps prevent lumps when they enter the hot sauce.
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10. Velg riktig svar.
Which property of lemon juice helps slow browning?
A cut apple gradually turns brown as enzymes react with oxygen. A little lemon juice can slow this process.
- Its sugar content.
- Its acidity.
- Its cloudy appearance.
Think about the conditions in which the enzymes work.
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- Its acidity.
Many browning enzymes work less effectively in acidic conditions. Lemon juice slows the process rather than stopping it forever.
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11. Velg riktig svar.
Why does leaving space help them brown?
Mushrooms release water as they cook. In the same oven, a crowded tray often gives paler results than a tray with space between the mushrooms.
- Extra space stops the mushrooms from releasing water.
- Extra space lowers the temperature at which water boils.
- Moisture escapes more easily, allowing the surfaces to dry.
A wet surface and a dry surface respond differently to heat.
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- Moisture escapes more easily, allowing the surfaces to dry.
Evaporating water keeps a wet surface relatively cool. A drier surface can get hot enough for faster browning.
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12. Velg riktig svar.
Why can the center keep getting warmer?
You remove a large roast from a hot oven. Although it is now on the counter, its center temperature continues rising briefly.
- Heat moves inward from the hotter outer layers.
- Cooking reactions create most of the heat inside the meat.
- The meat absorbs extra heat from the cooler kitchen air.
Different parts of the roast may still have different temperatures.
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- Heat moves inward from the hotter outer layers.
This is called carryover cooking. It tends to be more noticeable in larger cuts, so it matters when deciding when to remove a roast.