Potatoes become soft when cooked in salted water because the salt can penetrate the cells of the potatoes, causing a diffusion of water out of the cells, which softens them.
The cells of potatoes are surrounded by a fairly fragile membrane, whose mission is to maintain the balance between the inside and the outside. When salt is added to the cooking water, it changes the game by modifying this membrane. The salt draws water out of the cells through osmosis (a natural phenomenon where water prefers to move towards the saltier areas). As a result, the cells lose their initial firmness and become soft, as the protective barrier allows water and nutrients to pass through more easily. The cells deflate and weaken, in short, we end up with a potato that is more tender than it was at the start.
When you plunge a potato into salty water, a phenomenon occurs that we call osmosis. Basically, water moves from the potato cells (less salty) to the cooking water (more salty) to balance the concentrations. As a result, the cells lose their internal water, gradually emptying and becoming soft. The result: the potato gradually softens during cooking, and that's how you end up with the tender texture that mashed potato lovers adore.
When you cook a potato in salted water, the salt penetrates to the heart of the vegetable and directly attacks its reserve of starch. Normally, starch is organized into small, tightly packed granules. But in the presence of salt and under the effect of heat, these granules begin to absorb the salty water, swell, and become disorganized. This results in a sort of soft and less structured mass. The starch then loses its firmness and initial consistency. In other words, your good solid and firm potatoes become soft because the starch has diluted by absorbing salty water. The salt accelerates and intensifies this phenomenon, further promoting the softening of the vegetable.
Heat plays a key role in cooking potatoes, as it directly alters their internal structure. When the temperature rises, the cell walls become less resistant and eventually yield. At the same time, the starch granules, usually well compacted, swell by absorbing water, making the texture softer and more melting. That's why a slowly heated potato often remains a bit firm: it never really reaches the temperature needed to break all those internal bonds. In contrast, a high flame speeds up this phenomenon, quickly giving a tender and soft consistency to the whole. This is why precisely managing the temperature during cooking entirely determines the final texture of your potatoes.
It is not recommended to cook potatoes in heavily salted water if you want to make mashed potatoes: their starch is released more into the water, resulting in a sticky and unpleasant consistency.
Adding vinegar or a few drops of lemon juice to the cooking water helps to maintain the firmness of the potato by slightly reducing the degradation of the pectin present in their cell walls.
Salting the water before boiling slightly speeds up its arrival at the boiling point. However, this temperature increase is minimal (about 0.17 °C per tablespoon of salt per liter of water), thus having a negligible effect on the total cooking time.
Firm potatoes, such as Charlotte or Amandine, contain little starch and hold up better during prolonged cooking in salted water, thus maintaining their shape and texture more effectively.
Sure! Potatoes can definitely be cooked without salt. However, salt enhances their flavor and generally helps to tenderize them during cooking.
To cook potatoes in salted water while preserving their integrity, choose firm-fleshed varieties such as Charlotte or Ratte. In contrast, for a creamier or fluffier result, starchy varieties like Bintje are more suitable.
If your potatoes crumble easily during cooking, it may be due to a variety that is too starchy, prolonged overcooking, or an excessive amount of salt in the water, which greatly increases osmosis and breaks down the starch.
Yes, it is possible to use alternatives such as sea salt or flavored broths for cooking potatoes in order to enhance flavor without necessarily significantly increasing osmosis.
No, it mainly depends on the desired outcome. Adding salt at the beginning increases cellular permeability and promotes the softening of the potato. If you want to preserve more firmness, it is better to salt towards the end of cooking.
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