Steaming Water: Degrees Of Heat

Water is always evaporating and creating steam. The temperature at which this steam liquefies back into a mist depends on the air temperature and humidity. When water is heated at atmospheric pressure, its temperature rises until it reaches 212°F (100°C), the highest temperature at which water can exist at this pressure. Additional heat does not raise the temperature but converts the water to steam. This 'phase change' requires a lot of energy. Steam is invisible and always over 100°C.

Boiling point: 100°C/212°F

Water boils and becomes steam at 100°C (212°F). This is known as the 'boiling point'. At this temperature, water exists at its highest temperature under atmospheric pressure.

When water is heated, its molecules vibrate and some escape into the air as water vapour or steam. This process is called evaporation. As water continues to be heated, it will reach its boiling point and can no longer maintain its liquid state. It will then rapidly evaporate and turn into steam.

Steam is invisible and is distinct from vapour, which appears as a mist or fog. Vapour is diffused water molecules that have not yet reached the boiling point. When steam comes into contact with cooler air, it condenses back into tiny droplets of water, which we see as water vapour.

The boiling point of water is the same as its 'phase change' temperature. At this point, additional heat does not raise the temperature of the water but instead converts it into steam. This process requires a large amount of energy.

The temperature of steam can vary depending on the temperature of the burner and the surrounding conditions. However, in general, steam will escape at 100°C and will not reach a significantly higher temperature.

Steam is invisible

Steam is the name given to water when it is in a gaseous state. It is often thought of as a cloud of translucent mist, but this is actually the result of steam condensing in the air to form water vapour. In reality, steam itself is invisible.

When the atmospheric pressure is 1013 mbar (the average pressure at sea level), water will boil and turn into steam at 100°C. This is the boiling point. However, water is always evaporating and creating steam, even at temperatures below 100°C. The temperature at which this steam then turns back into a mist depends on the air temperature and humidity.

The "steam" produced by a hot shower, for example, is not actually steam but mist. Mist is made up of tiny droplets of liquid water. Steam only occurs at the boiling point and is invisible. What we often perceive as steam is actually fog, which is created when warm, moist air comes into contact with cooler air, causing the moisture in the air to condense into small drops. This can happen at a variety of temperatures and is influenced by the relative humidity.

So, while the steam itself is invisible, it can condense in the air to form water vapour, which is visible as a mist or fog.

Steam is water in gas form

Steam is water in its gaseous form. It is invisible and is always above 100 °C.

When water is heated at atmospheric pressure, its temperature rises until it reaches 100 °C (212 °F), the highest temperature at which water can exist at this pressure. At this point, additional heat does not raise the temperature but converts the water to steam. This process, known as a 'phase change', requires a significant amount of energy input. The ability of steam to carry large amounts of thermal energy is what makes it useful as a working fluid in steam engines.

The 'Latent Heat of Vaporization' explains why steam can carry so much thermal energy. Water heated from 32 °F to 212 °F contains 180 BTUs per pound. However, to convert 212 °F water to low-pressure steam, an additional 970 BTUs per pound are required. Increasing the pressure further increases the temperature of the phase change and the amount of energy the water/steam can carry.

Steam is often used for heating food, such as in pressure cookers, where some water turns into steam, and the steam is released through a valve. Steam is also used for sterilisation in autoclaves, where it kills microorganisms like bacteria, viruses, fungi and spores.

While steam itself is invisible, it is sometimes associated with a cloud of translucent mist. This mist is actually the steam condensing in the air, forming water vapour. The temperature at which this steam liquefies back into a mist depends on the air temperature and humidity.

Steam powers steam engines

The first steam-powered devices were invented in the first century AD by Hero of Alexandria, a Hellenistic mathematician and engineer in Roman Egypt. However, it wasn't until the 17th century that steam was harnessed for practical purposes. In 1698, Thomas Savery patented a steam-powered pump to remove water from mines. This was followed in 1712 by Thomas Newcomen's more efficient steam engine with a piston separating the condensing steam from the water.

In 1765, James Watt significantly improved the Newcomen engine by adding a separate condenser, preventing the cylinder from being heated and cooled with each stroke. Watt's engine also rotated a shaft instead of providing an up-and-down motion, making it a practical power plant. Further improvements were made by Richard Trevithick, who developed the use of high-pressure steam, and Matthew Murray, whose twin-cylinder locomotive Salamanca was used by the Middleton Railway.

By the 19th century, stationary steam engines were powering the factories of the Industrial Revolution. Steam engines were also used to propel ships and locomotives. However, by the early 20th century, advances in electric motors and internal combustion engines led to the gradual replacement of steam engines in commercial usage. Today, steam turbines are used to generate large quantities of electric power.

Steam is used for heating food

Steam is invisible and is always over 100 °C. It is water vapour, which can exist entirely below 100 °C. Water vapour is not called steam if it is under the boiling point. Steam's maximum temperature is 212 °F, just like water. However, unlike water, steam can be forced to exceed this temperature by being pressurised. The higher the pressure, the hotter the steam becomes.

Steam can be used to heat a wide variety of foods, from vegetables to proteins, buns, dumplings, and even desserts. Seafood is particularly well-suited for steaming, as the moist environment inside the steamer compartment helps keep the fish tender and juicy.

There are several ways to set up a steamer for heating food:

• A pot (or wok) with a lid and a heat-proof dish: This method requires a pot or wok with a lid, a heat-proof dish that fits inside the pot or wok, and something to prop up the dish above the water, such as a metal steam rack or a clean metal can.
• A stainless steel steamer: This type of steamer has multiple tiers, allowing for the simultaneous steaming of different types of food. It is easy to set up and clean, but condensation can collect on the lid and drip onto the food.
• A bamboo steamer: Bamboo steamers do not collect condensation like stainless steel steamers, so there is no risk of water dripping onto steamed food. However, they require more attention as the water level must be monitored to ensure it does not touch the bottom of the steamer or evaporate completely.

Frequently asked questions