The Heat Is On: Iron Vs. Boiling Water

Boiling water will always be 100°C, no matter how much extra heat is applied. However, the steam produced by boiling water can be hotter than the water itself, as it has been heated further. This is why steam can burn your hand more than the water itself.

Cast iron pans are known to get much hotter than other pans, even when on the same heat settings. This is because cast iron is excellent at transferring heat, so the entire pan gets heated, not just the bottom. Cast iron pans are also great at retaining heat, so they can stay hot for longer than other pans.

Boiling water will not increase in temperature, but it will accept more heat

The rate of heat transfer between two objects is directly proportional to the temperature difference between them. Therefore, a hotter stove will heat a volume of water to boiling point quicker than a cooler stove. However, once the water is boiling, the temperature difference between the heating surface and the water determines the rate at which the water reaches its boiling point.

If the heating surface is excessively hot, a steam blanket can form between the heating surface and the liquid, which insulates the liquid from the heating surface and greatly reduces heat transfer. This is known as the Leidenfrost effect.

Additionally, the temperature of boiling water can be increased by increasing the pressure inside the container. This is because the boiling point of water is dependent on the pressure of the air surrounding it. For example, at the summit of Mount Everest, water boils at 68°C.

Cast iron pans are excellent at transferring heat

Cast iron pans are also great for baking. You can use them for baking garlic knots or cornbread or the easiest, best pan pizza you'll ever bake. They are also great for a complete chicken dinner with insanely crisp skin and for crispy, creamy pasta bakes.

Cast iron pans are slow to heat up, so they're also slow to cool down. They retain their temperature longer than other materials and won't produce temperature spikes. Cooking with cast iron is more akin to driving a boat than a car: the pan doesn't respond instantly to changes in the applied heat. This behaviour can be disconcerting to the uninitiated.

Cast iron pans are naturally non-stick when seasoned properly. New cast iron is anything but non-stick, and it can easily rust. Seasoning—rubbing oil or fat into the cast iron and subsequently heating it—fixes both problems. Unsaturated fats work best. Nineteenth-century American cooks typically used lard because it was readily available and unsaturated enough to polymerize well, but almost any oil will work. When an unsaturated fat is heated to high temperatures, especially in the presence of a good catalyst like iron, it is broken down and oxidised, after which it polymerises—joins into larger mega molecules the same way plastics do—and mixes with bits of carbon and other impurities. This tough, impermeable surface adheres to the pores and crevices in the cast iron as it is forming. The surface is non-stick because it is hydrophobic – it hates water. Water-soluble proteins make foods stick to their pan; a hydrophobic surface prevents sticking. The bits of carbon in the seasoning may also act as an additional release agent.

Cast iron pans are also great for outdoor cooking. They will transform your gas grill and really help you step up your grilling game! Pop a cast iron skillet or griddle on the grill to prepare small or delicate foods that are difficult to cook directly on the grill grate—think fish, veggies, pizza, and smash burgers. Or use a dutch oven to simmer baked beans while you cook the brats directly on the grill.

Boiling water will not increase in temperature, but the steam it produces will burn you more

Boiling water will always remain at the same temperature, which is 100°C (212°F). However, the steam produced by boiling water will burn you more. This is because steam contains more energy than boiling water.

When water reaches its boiling point, it turns into steam. Steam is made up of superheated water molecules. When these molecules come into contact with your skin, they release their energy, which, along with the heat, contributes to the severity of the burn.

The human perception of hot and cold is not based on temperature but on heat flow (the amount of heat transferred per unit of time). Therefore, when steam condenses on your skin, a large amount of thermal energy is transferred, causing a more severe burn.

Additionally, steam can cause worse burns than hot water due to its ability to escape under pressure in jets or streams. This pressurised steam can cause injury when it comes into contact with your skin or eyes. It can also be easily inhaled, causing burns in the airways and nose, mouth, and throat.

The bottom of a pan of boiling water will be the hottest part

Additionally, the type of heat source can also affect the temperature distribution in the pan. For example, with a gas burner, the flames come into direct contact with the pan, creating a ring of hot spots where the flames touch the pan. In contrast, an electric burner may create a more even heat distribution across the bottom of the pan.

Furthermore, the materials that the pan is made of can also influence the hot and cold spots. Different materials have varying heat conduction properties, which can affect how efficiently heat is transferred to the water.

It is important to note that while the bottom of the pan may be the hottest part, the water temperature will remain constant at the boiling point, which is 100°C at sea level. Increasing the heat will not raise the temperature of the water but will instead increase the rate of evaporation, creating more steam.

Boiling water will not increase in temperature, but it will evaporate faster

When water reaches its boiling point, adding more heat will not increase its temperature. Instead, the extra heat is used to convert the water from a liquid to a gas, through a process called evaporation. This is why boiling water evaporates faster than water at room temperature.

Evaporation is the process by which individual molecules of a liquid gain enough energy to escape from the surface and become a gas. This can occur at any temperature above freezing, and the rate of evaporation depends on factors such as temperature, humidity, and surface area. Boiling, on the other hand, is a much faster process that occurs when the liquid reaches its boiling point.

It's important to note that while the temperature of boiling water remains constant, the temperature of the steam generated can be higher. This is because steam at 100°C contains more heat than liquid water at the same temperature, as energy is required to turn the liquid water into water vapour.

Additionally, the bottom of a pot of boiling water may be slightly hotter than the top due to the heat source being applied unevenly. However, once a rolling boil is achieved, the entire pot of water is at the boiling point, and the temperature remains constant.

Frequently asked questions