How to boil water correctly and what temperature is needed to brew tea. How to properly heat water for tea When boiling, what degree is the water

Ordinary water boils at 100 degrees - we do not doubt the validity of this statement, and the thermometer easily confirms this. However, there are people who can smile skeptically, because they know - water does not always and everywhere boil at exactly 100 degrees.

Is this possible? Yes, it is possible, but only under certain conditions.

It must be said right away that water can boil at temperatures both below and above +100 ° C. So do not be surprised by the expression "Water boiled at + 73 ° C" or "Water began to boil at + 130 ° C" - both of these situations are not only possible, but also relatively easy to implement.

But in order to understand how to achieve the effects just described, it is necessary to understand the mechanism of boiling water and any other liquids.

When the liquid is heated near the bottom and on the walls of the vessel, bubbles filled with steam and air begin to form. However, the temperature surrounding water is too small, which is why the vapor in the bubbles condenses and contracts, and under the pressure of water, these bubbles burst. This process continues until the entire volume of the liquid does not warm up to the boiling point- at this moment, the pressure of steam and air inside the bubbles is compared with the pressure of water. Such bubbles are already able to rise to the surface of the liquid, releasing steam into the atmosphere there - this is boiling. During boiling, the temperature of the liquid no longer rises, since thermodynamic equilibrium sets in: how much heat is spent on heating, the same amount of heat is removed by steam from the surface of the liquid.

The key point in boiling water and any other liquid is the equality of the vapor pressure in the bubbles and the water pressure in the vessel. A simple conclusion can be drawn from this rule - a liquid can boil at completely different temperatures, and this can be achieved by changing the pressure of the liquid. As you know, the pressure in liquids consists of two components - its own weight and air pressure above it. It turns out that it is possible to lower or raise the boiling point of water change in atmospheric pressure or pressure inside a vessel with a heated liquid.

In fact, this is what happens. For example, in the mountains, boiling water is not at all as hot as on the plains - at an altitude of 3 km, where the air pressure drops to 0.7 atmospheres, the water boils already at +89.5 degrees. And on Everest (height - 8.8 km, pressure - 0.3 atmospheres), water boils at a temperature of slightly more than +68 degrees. Yes, cooking at such temperatures is a very difficult task, and if it were not for special means, then at such heights it would be completely impossible.

To increase the boiling point, it is necessary to increase the pressure of the atmosphere, or at least tightly close the vessel with water. This effect is used in the so-called pressure cookers- a tightly closed lid does not allow steam to escape, due to which the pressure in it rises, which means that the boiling point also rises. In particular, at a pressure of 2 atmospheres, water boils only at +120 degrees. And in steam turbines, where a pressure of tens of atmospheres is maintained, water does not boil even at + 300-400 ° C!

However, there is another possibility of heating water up to high temperatures without boiling. It has been observed that the formation of the first bubbles begins at the roughness of the vessel, as well as around more or less large particles of contaminants present in the liquid. Therefore, if you heat an absolutely pure liquid in perfectly polished vessel, then at normal atmospheric pressure it is possible to make this liquid not boil at very high temperatures. The so-called superheated liquid, characterized by extreme instability - a minimal push or a speck of dust is enough for the liquid to instantly boil (and in fact, literally explode) immediately in its entire volume.

Ordinary water, with some effort, can be heated to +130 ° C and it will not boil. To obtain high temperatures, it is already necessary to use special equipment, but the limit occurs at +300 ° C - superheated water at this temperature can exist for a fraction of a second, after which it occurs explosive effervescence.

Interestingly, a superheated liquid can also be obtained in another way - by heating it to a relatively low temperatures(slightly below +100 °C) and sharply reduce the pressure in the vessel (for example, by a piston). In this case, a superheated liquid is also formed, capable of boiling with minimal impact. This method used in bubble chambers registering charged elementary particles. When flying through a superheated liquid, a particle causes its local boiling up, and externally this is displayed as the appearance of a track (trace, thin line) from microscopic bubbles. However, it is not water that is used in bubble chambers, but various liquefied gases.

So, water does not always boil at +100 ° C - it all depends on pressure. external environment or inside a vessel. Therefore, in the mountains special means it is impossible to get "normal" boiling water, and in the boilers of thermal power plants, water does not boil even at +300 °C.

To prepare various delicious food, water is often needed, and if it is heated, it will boil sooner or later. Everyone educated person at the same time, he knows that water begins to boil at a temperature equal to one hundred degrees Celsius, and with further heating its temperature does not change. It is this property of water that is used in cooking. However, not everyone knows that this is not always the case. Water may boil at different temperature depending on the conditions in which it is located. Let's try to figure out what the boiling point of water depends on, and how to use it.

When heated, the temperature of the water approaches the boiling point, and numerous bubbles form throughout the volume, inside which there is water vapor. The vapor density is less than the density of water, so the Archimedes force acting on the bubbles lifts them to the surface. At the same time, the volume of bubbles either increases or decreases, so boiling water makes characteristic sounds. Reaching the surface, the bubbles with water vapor burst, for this reason, boiling water gurgles intensely, releasing water vapor.

The boiling point explicitly depends on the pressure exerted on the surface of the water, which is explained by the dependence of the pressure of saturated vapor in the bubbles on temperature. In this case, the amount of vapor inside the bubbles, and with it their volume, increase until the saturation vapor pressure exceeds the water pressure. This pressure is the sum of the hydrostatic pressure of water, due to the gravitational attraction to the Earth, and the external atmospheric pressure. Therefore, the boiling point of water increases with increasing atmospheric pressure and decreases with its decrease. Only in the case of normal atmospheric pressure of 760 mm Hg. (1 atm.) water boils at 100 0 C. The graph of the dependence of the boiling point of water on atmospheric pressure is presented below:

It can be seen from the graph that if we increase Atmosphere pressure up to 1.45 atm, then the water will boil already at 110 0 C. At an air pressure of 2.0 atm. water will boil at 120 0 C and so on. Increasing the boiling point of water can be used to speed up and improve the cooking process of hot foods. To do this, they invented pressure cookers - pans with a special hermetically sealed lid, equipped with special valves to regulate the boiling temperature. Due to tightness, the pressure in them rises to 2-3 atm., which provides a boiling point of water of 120-130 0 C. However, it must be remembered that the use of pressure cookers is fraught with danger: the steam coming out of them has high pressure and high temperature. Therefore, you need to be as careful as possible so as not to get burned.

The opposite effect is observed if the atmospheric pressure decreases. In this case, the boiling point also decreases, which happens with an increase in altitude above sea level:

On average, when climbing 300 m, the boiling point of water decreases by 1 0 C and quite high in the mountains drops to 80 0 C, which can lead to some difficulties in cooking.

If, however, the pressure is further reduced, for example, by pumping air out of a vessel with water, then at an air pressure of 0.03 atm. water will boil already at room temperature, and this is quite unusual, since the usual boiling point of water is 100 0 C.

Boiling water is required for a variety of purposes, and the ability to boil water is simply necessary in everyday (and not only) life. Are you preparing lunch? Knowing how salt affects the boiling of water and how to cook poached eggs will come in handy. Are you climbing to the top of the mountain? You will probably be interested in why food takes so long to cook in the mountains, and how to make the water from the river you meet safe to drink. After reading this article, you will learn about these and many other interesting things.

Steps

Boiling water while cooking

Take a saucepan with a lid. The lid will keep the heat inside the pot and the water will boil faster. In a large pot, water boils more slowly, but the shape of the pot does not play a significant role.

Pour cold tap water into a saucepan. Hot water from a faucet can absorb lead from water pipes, so it is better not to use it for drinking and cooking. So, fill a pot with cold water. Don't fill the pot to the top so that the water doesn't slosh when it boils, and be sure to leave room for the food you're going to cook in the pot.

Add salt for taste (optional). Salt has almost no effect on the boiling point, even if you pour so much salt that the water turns into sea water! Add some salt to add flavor to your food - for example, pasta absorbs salt along with water when cooked.

Place the saucepan over high heat. Put a pot of water on the stove and turn on a strong fire under it. Cover the pot with a lid to make the water boil a little faster.

Distinguish between boiling stages. Most dishes require simmering or vigorous water to cook. Learn to recognize these boiling stages, as well as a few other clues about water temperature:

• Jittering: small bubbles of gas form at the bottom of the pan, but do not rise to the surface. The surface of the water trembles slightly. It occurs at 60–75ºC (140–170ºF), suitable for poached eggs, fruits, and fish.
• Boiling: a few streams of air bubbles rise to the surface of the water, but in the bulk the water remains calm. The water temperature is around 75-90ºC (170-195ºF), which is good for making stews or stews.
• Slow boil: rises to the surface of the water over the entire area of ​​the pan a large number of small and medium bubbles. The water temperature is 90-100ºC (195-212ºF), which is suitable for steaming vegetables or hot chocolate, depending on your mood and well-being.
• Full, violent boil: steam is released, the water is bubbling, and the bubbling does not stop when stirred. The maximum water temperature is 100ºC (212ºF). It is good to cook pasta in such water.

1. Put food in the water. If you are going to boil any food, place it in water. Being cold, they will lower the temperature of the water, and it may stop boiling. This is in order: just put a large or medium heat under the pan and wait until the water warms up again to the desired temperature.

   Turn off the fire. A strong fire is needed in order to quickly bring the water to a boil. When the water comes to a boil, reduce the heat to medium (for a strong boil) or low (for a slow boil). After the water reaches last stage boiling, a strong fire is not needed, as it will only make the boil more violent.

   • Watch the pot for a few minutes, making sure the water is boiling the way you want it to.
   • If you are cooking soup or any other dish that requires a long cooking time, open the pot slightly by sliding the lid to one side. In a tightly closed pot, the temperature will be slightly higher than required for cooking these dishes.

   Drinking water purification

   Boil water to kill bacteria and other pathogens it contains. When water is boiled, almost all microorganisms die in it. However, boiling not rid the water of chemical contamination.

   • If the water is cloudy, filter it to remove dirt particles.

2. Bring the water to a vigorous boil. Microorganisms die due to high temperature, not from boiling. However, without a thermometer, it is difficult to determine the temperature of the water until it boils. Wait for the water to boil and release steam. In this case, all dangerous microorganisms will die.

   Boil water for 1-3 minutes (optional). To be sure, let the water boil for 1 minute (slowly count to 60). If you are above 2,000 meters (6,500 feet) above sea level, boil the water for 3 minutes (count slowly to 180).

   • The boiling point of water decreases with height. At lower temperatures, it will take longer to kill microorganisms.

3. Cool the water and pour it into a resealable container. Boiled water drinkable even after cooling. Keep it in a clean, closed container.

   Carry a compact water boiler with you when you travel. If you have access to sources of electricity, stock up on a boiler. Otherwise, take a camping stove or kettle with you, as well as heating fuel or batteries.

   If there are no other options, place a plastic container of water in the sun. If you are unable to boil water, pour it into a clean Plastic container. Place the water container in direct sunlight for at least six hours. This way you will destroy harmful bacteria, but this method is less reliable than boiling.

   Boiling water in the microwave

   Pour water into a microwaveable cup or bowl. If you don't have microwave-safe utensils handy, take a glass or ceramic container, not containing metallic paint. To test, place an empty container in the microwave with a ceramic cup filled with water next to it. Turn on the oven for one minute. If after that the container warms up, it not suitable for microwave oven.

   Place something safe for microwave use in the water. It will also make vaporization easier. Use a wooden spoon, chopstick or ice cream stick. If you don't need pure water without impurities, you can add a spoonful of salt or sugar to it.

   • Do not use plastic containers with a smooth inner surface - this will make it difficult to steam.

4. Place a bowl of water in the microwave. In most microwave ovens, the edges of the turntable heat up faster than the middle of the turntable.

5. Heat the water in short intervals, stirring occasionally. For safety reasons, check your microwave oven's instruction manual for the recommended time to heat water. If you don't have oven instructions, try heating the water in 1-minute intervals. After every minute, gently stir the water and take it out of the oven, checking its temperature. If the container is very hot and the water releases steam, it is ready.

   • If the water remains cold after a few minutes of heating, increase the interval to one and a half to two minutes. The heating time depends on the power of the microwave oven and the amount of water.
   • Don't try to reach the "boiling" stage in the microwave. Although the water will warm up to the required temperature, the boiling process will be less pronounced.

Anton

Gennady  The boiling point of water is 100 degrees.

from 85 to 110 depending on pressure. Alyona.

Artem  depends on pressure. if high above sea level, then water boils at temperatures less than 100 degrees

Boris  100 degrees Celsius at the time of shutdown. If it's boiling water. The temperature is higher - it's already steam.

Sasha  98 degrees

Svetlana  temperature... 99.9 ... karoch about 100 degrees)))

Egor  There is the temperature at which the thermostat is set. Plus or minus error.

Peter  temperature exceeds 100Fyodor

Oksana  100 degrees... and went downhill...

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Tea brewing temperature

How to simply ensure the temperature of tea brewing if the kettle has no temperature controller and no thermometer?
Boil water, and cool, diluted with water at room temperature in a certain proportion.
For example, you need water for brewing at a temperature of 80 degrees.
1. Pour a liter of water into the kettle, bring to a boil.
2. We are waiting for the boiling to stop.
3. After the boiling stops, pour one and a half glasses of water at room temperature into the kettle.
4. Immediately pour into the teapot, and it will be 80 degrees.
What is happening there?
Step by step.
AT normal conditions(I don’t consider mountain) water boils at 100 degrees.
1. Pour a liter of water into the kettle, bring to a boil. This will get the temperature very close to 100 degrees. Boiling takes place at a constant temperature.
2. We are waiting for the boiling to stop. By diluting, we want to lower the temperature of the water in the kettle, and not waste its energy consumption also on stopping boiling.
3. After the boiling stops, pour one and a half glasses of water at room temperature into the kettle. Why one and a half?
How much water to add? Unknown volume = X.
It was: 1000 ml * 100 degrees + X ml * 25 degrees.
Now: 1000 ml * 80 degrees + X ml * 80 degrees.
1000 * 100 + X * 25 = 1000 * 80 + X * 80,
1000 * 100 - 1000 * 80 = X * 80 - X * 25,
X \u003d 20000 / 55 \u003d 364 ml.
It's about a glass and a half.
Given the heat capacity of the teapot and teapot (heavy and unheated teapot), you can pour less.

At what temperature does water boil? | Q&A | Around...

31 Mar 2007 ... It would seem that the answer to this question is obvious - water boils at 100°C and freezes at 0°C (strictly adhering to physical...

If you are asked at what temperature water boils, you will most likely answer that at 100 ° C. And your answer will be correct, but this value is only true at normal atmospheric pressure - 760 mm Hg. Art. In fact, water can boil at both 80°C and 130°C. In order to explain the reason for such discrepancies, it is first necessary to clarify what boiling is.

To figure out how many degrees are needed for the water to boil, studying the mechanism of this will help. physical phenomenon. Boiling is the process of converting liquid into vapor and takes place in several stages:

1. When the liquid is heated, bubbles with air and water vapor come out of the microcracks in the walls of the vessel.
2. The bubbles expand a little, but the liquid in the vessel is so cold that the vapor in the bubbles condenses.
3. The bubbles begin to burst until the entire thickness of the liquid becomes hot enough.
4. After some time, the pressure of water and steam in the bubbles equalize. At this stage, individual bubbles can rise to the surface and release steam.
5. The bubbles begin to rise intensively, seething begins with a characteristic sound. Starting from this stage, the temperature in the vessel does not change.
6. The boiling process will continue until all the liquid passes into a gaseous state.

Steam temperature

The temperature of the steam when water boils is the same as that of the water itself. This value will not change until all the liquid in the vessel has evaporated. During the boiling process, wet steam is formed. It is saturated with liquid particles uniformly distributed throughout the entire gas volume. Further, highly dispersed liquid particles condense, and saturated steam turns dry.

There is also superheated steam, which is much hotter than boiling water. But it can only be obtained with the help of special equipment.

Pressure influence

We have already found out that for a liquid to boil, it is necessary to equalize the pressure of a liquid substance and vapor. Since water pressure is the sum of atmospheric pressure and the pressure of the liquid itself, there are two ways to change the boiling time:

• change in atmospheric pressure;
• change in pressure in the vessel itself.

The first case we can observe in the territories located on different height above sea level. On the coasts, the boiling point will be 100 ° C, and at the top of Everest - only 68 ° C. The researchers calculated that when climbing mountains, the boiling point of water drops by 1 °C every 300 meters.

These values ​​may vary depending on chemical composition water and the presence of impurities (salts, metal ions, soluble gases).

Kettles are most often used to get boiling water. The boiling point of water in a kettle also depends on where you live. Residents highlands it is recommended to use autoclaves and pressure cookers, which help to make boiling water hotter and speed up the cooking process.

Boiling salt water

The temperature at which water boils determines the presence of impurities in it. As part of sea ​​water sodium and chloride ions are present. They are located between the H2O molecules and attract them. This process is known as hydration.

The bond between water and salt ions is much stronger than between water molecules. It takes more energy to boil salt water so that these bonds can be broken. This energy is temperature.

Also, salty liquid differs from fresh water by a low concentration of H2O molecules. In this case, when heated, they begin to move faster, but they cannot form a sufficiently large vapor bubble, since they collide less often. The pressure of small bubbles is not enough to bring them to the surface.

To equalize water and atmospheric pressure, you need to increase the temperature. Therefore, salt water takes much longer to boil than fresh water, and the boiling point will depend on the salt concentration. It is known that adding 60 g of NaCl to 1 liter of liquid increases the boiling point by 10 °C.

How to change the boiling point

In the mountains it is very difficult to cook food, it takes too much time. The reason is not enough hot boiling water. For a very high altitudes it is almost impossible to boil an egg, let alone cook meat that needs a good heat treatment.

Changing the temperature at which the liquid boils is important for residents not only of mountainous areas.

For sterilization of products and equipment, it is desirable to use a temperature higher than 100 °C, as some microorganisms are heat resistant.

This is important information not only for housewives, but also for professionals working in laboratories. Also, increasing the boiling point can significantly save time spent on cooking, which is important in our time.

To increase this figure, you need to use a tightly closed container. Pressure cookers are best suited for this, in which the lid does not allow steam to pass through, increasing the pressure inside the vessel. During heating, steam is released, but since it cannot escape, it condenses on inside covers. This leads to a significant increase in internal pressure. In autoclaves, the pressure is 1–2 atmospheres, so the liquid in them boils at a temperature of 120–130 °C.

The maximum boiling point of water is still unknown, since this figure can increase as long as atmospheric pressure increases. It is known that water cannot boil in steam turbines even at 400 °C and a pressure of several tens of atmospheres. The same data was obtained from great depths ocean.

Boiling Water Under Reduced Pressure: Video