Ice is used in cooking to cause one thermal shock, a technique that exploits a rapid and marked change in temperature to control the physical and chemical transformations of foods. Depending on the context it can be used for block unwanted processeswhich can lead to the formation of dark spots, as in the case of whitening of vegetables, where they are first blanched in hot water and then immersed in water and ice for preserve consistency and bright colors. Ice is also used for modular thermal energy, as happens when an ice cube is introduced into a pan during cooking: the ice absorbs part of the heat as latent heat, avoiding excessive overheating of the food.
Why vegetables darken: the reaction
When a vegetable or tuber is cut, peeled or grated, from a microscopic point of view we are damaging and breaking their cells. In this way, components that were previously separated into different compartments find themselves interacting with each other. For example, compounds called polyphenols (organic molecules very present in the plant world) come into contact with both environmental oxygen (OR2) and with specific enzymes, such as i polyphenol oxidase (PPO). This meeting promotes oxidation reactions which transform the polyphenols first into quinones and then, reacting with amino acids and proteins, into dark pigments called melanins. It is precisely these that cause thebrowning of food, that is, that phenomenon in which the surface takes on brown/dark shades, and which is accelerated by the processing of the food in the kitchen.
How to use ice when cooking and what it is used for
We can counteract this natural phenomenon resort to bleaching of vegetables. The technique first involves immersing the food in boiling water: high heat denature (therefore inactivates) the enzymes responsible for the reactions that lead to browning. Immediately after, you have to dip the food in water and ice: cooling will immediately stop cooking and will prevent the heat from ruining the texture (i.e. consistency) and appearance of the food. Let’s think, for example, of spinach or basil leaves: in the final dish do we want a dull color or a nice bright green? Even in the kitchen the eye wants its part, and cold temperatures allow it to maintain a more vivid appearance, maintaining the natural color of the food.
This technique which involves a rapid passage from room temperature to first very high and then very low temperatures, is an example of thermal shockthat is, a rapid and sudden change in temperature.
Ice during cooking
You may have seen some videos or heard some relatives who use ice even while cooking, for example, a pan-fried steak. Although there are no scientific studies dealing with this particular technique, we can use some notion of physics to explain what happens.
Let’s go back to pan-fried steak: good cooking involves the formation of a “layer” around the meat (what we call a crust) which can function a bit like a protective barriercapable of protecting the inside of the food from overcooking. The crust is formed following a series of chemical processes such as Maillard reactionwhich occurs between proteins and sugars on the surface of the meat. However, this barrier that is formed is not a barrier waterproof seal: the heat continues to spread inwards during cooking and this can lead to an excessive release of liquids resulting in drynessin addition to the risk of burning the surface.
This is where it comes into play physics: adding one or two ice cubes to the pan does not ruin the cooking, on the contrary, it helps control the thermal energy of the system ensuring that the heat does not transfer only and exclusively to the meat. In fact, the ice will absorb part of the thermal energy in the form of latent heatthat is, the heat that ice uses to break the bonds that hold its solid structure together, passing into a liquid state. The ice therefore absorbs a large amount of energy which is removed from the cooking environment. In practice, ice works as a kind of thermal shock absorber: it does not cool the meat, but redistributes the available thermal energy, preventing it from being all concentrated on the steak.
Once the ice melts, the water comes into contact with the hot surface of the pan and turns into steam. This could have a further positive effect: Steam can transfer heat to the meat more uniformly and less aggressively, also reducing excessive surface dehydration. You just have to be careful not to overdo it with the amount of ice: the risk is that you get boiled meat once it is transformed into water!
