Can water reach a state that’s hotter than hell? Check out this article, where we’ll unravel the Leidenfrost spell.
What exactly is boiling?
The technical definition is when a liquid’s vapor pressure is greater than or equal to atmospheric pressure.
Basically, even though liquid water molecules tend to like each other and stick together, when enough energy is given to them (in the form of heat), they get so hyperactive that an attempt is made to jump up and off into the atmosphere. At the same time, molecules of air (mostly nitrogen and oxygen) are bumped down onto the surface of the water, trying to keep them in line. At reasonable temperatures, a pretty good job is done by the air in keeping the water in check, allowing only a few molecules to jump up and away. But, with enough heat, the outward pressure of the water vapor trying to escape will exceed that of the air pressing it down. The floodgates are opened, and water molecules are rapidly transitioned from a liquid state to a gas.
This conversion of liquid water to water vapor (steam) is what is observed when a pot of boiling water is looked at.
As is known, for pure water at standard pressure (the air pressure that exists at sea level), the temperature at which this occurs is 212°F / 100°C. But what kind of things can affect this temperature, and what does it all mean for our cooking?
Quiver, Bubble, Simmer and Boiling
In recipes, terms such as “simmer,” “quiver,” and “boil” are frequently used without providing a comprehensive technical definition. Here’s a brief overview of what occurs when a pot of water is brought to a boil:
- 140 to 170°F / 60 to 77°C
The “quiver” phase begins. During this stage, small water vapor bubbles start forming at nucleation sites (more on those later) along the bottom and sides of the pan. While these bubbles are not large enough to rise to the water’s surface, their formation causes a slight vibration on the top surface, resulting in the “quiver” effect. This temperature is perfect for gently poaching meats, fish, and eggs (around 160°F or 71°C is the standard temperature if we don’t want to wait hours for proteins to cook).
- 170 to 195°F / 77 to 90°C
This is the sub-simmer phase. Bubbles from the sides and bottom of the pot begin rising to the surface. We can observe a couple of streams of tiny, champagne-like bubbles ascending from the pot’s bottom. However, the liquid remains relatively calm for the most part. This temperature range is ideal for tasks like making stock or slow-cooking gentle braises and stews. Lower temperatures would prolong cooking times, while higher temperatures could risk drying out the meat.
- 195 to 212°F / 90 to 100°C
Now, we reach the full simmer stage. Bubbles consistently break the surface of the pot, emerging from various points rather than just a few individual streams as seen during sub-simmer. This temperature is suitable for using a steamer basket above the water, melting chocolate, or preparing items like hollandaise in a double boiler.
- 212°F / 100°C
The full rolling boil stage is attained. This is the familiar scenario where water is vigorously boiling. It’s used for blanching vegetables, cooking pasta (using the traditional method), and various other applications.
Altitude and Boiling Point
The altitude or more precisely the pressure that comes from altitude changes disrupts various recipes.
- Beans don’t cook properly
- Pasta remains stubbornly firm
- Stews demand more time for braising
- Pancakes can over-inflate and deflate
If one ascends far enough, even cooking vegetables, which must be heated to at least 183°F / 83°C to break down, becomes unfeasible.
For certain problems like stews, dry beans, and root vegetables, a pressure cooker can be a lifesaver. It operates by creating a vapor-tight seal around the food. As the water inside heats up and turns into steam, the pressure inside the pot increases (since steam occupies more space than water). This heightened pressure prevents the water from boiling, enabling us to attain much higher temperatures than we could in the open air. Most pressure cookers permit cooking at temperatures between 240 and 250°F / 122°C, regardless of elevation.
Regarding the other altitude-related effects (poached eggs, pancakes, etc.), unfortunately, there are no universal solutions to apply across the board.
Cold Taps, Previously Frozen Water, and Other Myths
- Cold water is boiled faster than hot water
This assertion lacks any logical basis and is entirely untrue. It’s remarkably easy to demonstrate its falseness. Nevertheless, it’s somewhat surprising that this misconception endures. Nonetheless, there is a valid reason to opt for cold water over hot when cooking: hot water may contain a higher concentration of dissolved minerals from the water pipes, potentially imparting an undesirable taste to our food, especially if we reduce the water significantly.
- Water that has been frozen or previously boiled boils faster
This myth possesses some scientific underpinning. Boiling or freezing water eliminates dissolved gases, primarily oxygen, which can marginally affect the boiling point. However, the effect is so minimal that neither any observable difference nor any distinction could be detected using a timer or thermometer.
- Salt elevates the boiling point of water
True… to an extent.
Dissolved solids such as salt and sugar do, in fact, raise the boiling point of water, causing it to reach a boil more slowly. Nevertheless, the impact is negligible (the typical quantities used in cooking result in less than a 1-degree change). To make any noteworthy difference, one would need to incorporate it in exceedingly large quantities. Thus, for the most part, this notion can be disregarded.
- Alcohol completely evaporates during cooking
This notion seems logical at first glance. Water boils at 212°F / 100°C, and alcohol boils at approximately 173°F / 78°C, so it might appear that the alcohol will entirely vaporize long before any noticeable impact is made on the water. Unfortunately, that’s not the case. Even after three hours of simmering, approximately 5% of the original alcohol in our stew will remain. If we cook it with the lid on, this figure can increase by up to ten times. While this amount of alcohol is generally inconsequential for most people, it’s worth considering for those who abstain from alcohol.
The addition of a handful of salt to simmering or boiling water indeed gives the impression of causing it to boil rapidly. This occurs because of the presence of minute entities known as nucleation sites, which essentially serve as the birthplaces of bubbles. In order for steam bubbles to form, there must be some form of irregularity within the water volume—microscopic imperfections on the pot’s inner surface will suffice, as will tiny specks of dust or the pores of a wooden spoon. A handful of salt swiftly introduces thousands of nucleation sites, greatly facilitating the formation and release of bubbles.
On a much grander scale, entire galaxies came into existence as matter began to accumulate in gravitational wells initially formed by minuscule nucleation sites in the early universe. #Mindblowing
As is commonly understood, water is comprised of individual molecules, each consisting of two hydrogen atoms and one oxygen atom (H₂O). The swifter the motion of these molecules, the higher the water’s temperature becomes. These molecules possess a magnetic charge, rendering them susceptible to the influence of electromagnetic radiation (which, incidentally, is not as ominous as it may sound—both the light perceivable by our eyes and the heat sensed on our skin are forms of electromagnetic radiation). Microwaves make strategic use of this principle by emitting waves that instigate the rapid back-and-forth oscillation of water molecules. This kinetic activity, in turn, results in the heating of our food.
Due to the minimal dissipation of energy to the external environment (unlike, for instance, a gas burner that warms the room), microwaves exhibit exceptional efficiency in heating water. They prove highly effective for rapidly bringing water to a boil without elevating the temperature of the living space. An electric kettle also excels in this regard.
When water is heated in an immaculate container with minimal disturbance (as in the microwave, for instance), it can actually be heated well beyond its boiling point without undergoing the boiling process due to the absence of nucleation points.
The introduction of even slight turbulence, such as a minor wobble caused by the turntable, triggers the release of bubbles, resulting in hot water dispersing throughout the interior of our microwave. This phenomenon does not occur on the stovetop, as the heating from the bottom of the pot generates numerous convection currents (the motion that arises between regions of liquid or gas with varying temperatures).
Real world applications
Let’s assume we are preparing a stew in the oven. We place our Dutch oven inside, set the temperature to a moderate 275°F / 135°C, and step aside. One might think that the water will eventually reach a boiling point of 212°F / 100°C, correct?
Actually, that’s not the case. Due to the cooling effect resulting from evaporation (it requires a substantial amount of energy for those water molecules to transition from the liquid’s surface—a form of energy they extract from the liquid itself, thus causing it to cool down), an open pot of stew in a 275°F / 135°C oven will reach a maximum temperature of approximately 185°F / 85°C. The good news is that this temperature falls within the optimal sub-simmer stewing temperature range.
However, when we place the lid on the pot, the level of evaporation diminishes. Reduced evaporation leads to a higher maximum temperature. Covering the pot increases the temperature within by nearly 25°F / 14°C!
Two identical pans are in our possession. One is kept at 300°F / 149°C on a burner, and the other is maintained at 400°F / 204°C. We then introduce half an ounce of water into each pan and measure the time it takes for the water to evaporate.
Fascinatingly the water in the 400°F / 204°C pan will actually take longer to evaporate.
The principle was initially observed by Johann Gottlob Leidenfrost, an 18th-century German doctor. It turns out that if we provide a drop of water on a pan with enough energy, the steam it produces will exert such force that it will lift the water droplet entirely off the pan’s surface. No longer in direct contact with the pan and insulated by this layer of steam, the transfer of energy between the pan and the water becomes quite inefficient, resulting in a prolonged evaporation process.
This effect can be rather advantageous in the kitchen.
Drop a bead of water on a pan while heating it. If
- it stays on the surface and evaporates rapidly, our pan is below 350°F / 177°C or so—a sub-optimal temperature for most sautéing and searing.
- the pan is hot enough for the Leidenfrost effect to occur, the water will form distinct drops that glide and skid across the surface of the metal, taking quite a while to evaporate. The pan is hot enough for cooking.
When heating cold milk in a pot slowly, results in a layer of browned proteins stuck to the bottom of the pot, try preheating the pot next time before adding the milk. The Leidenfrost effect will prevent the milk from coming into direct contact with the pan during the initial heating phase, effectively preventing the milk from scorching.
Ever tried searing in a freshly got stainless steel skillet and ended up banning such kitchenware from the kitchen for an eternity? It happened because of the Leidenfrost effect wasn’t at full force. Always heat up stainless steel skillets and make the water droplet test before adding anything to them.
- Boiling is when a liquid’s vapor pressure equals or exceeds atmospheric pressure due to added heat.
- The four boiling stages are quiver, bubble, simmer and boiling each happens at different temperatures hence suitable for different cooking tasks.
- Altitude affects recipes; pressure cookers help.
- Cold water boiling is not faster nor can we cook away alcohol.
- Microwave ovens can heat water higher then boiling point so be careful there!