Salt is the key here. Water will move from an area of less salt to more salt (more water to less water), and so when the potato is placed in the saltwater, all the water that is inside the potato (yes, plants have a lot of water inside of them, that's what gives a plant it's structure) moves out by osmosis.
The potato in the salt water shrinks because water moves from the potato into the more concentrated salt water. In contrast, water moves from the less concentrated distilled water into the potato causing it to expand.
Place one potato half into each dish with the cut/flat side down – watch what happens after about 30 minutes. The salt water draws the water out of the potato, causing it to shrivel. Like the potato, salty food and drinks make people thirsty.
If keeping potatoes in water for more than an hour, refrigerate. However, don't soak them any longer than overnight—after that, the potatoes start to lose their structure and flavor.
We usually recommend no more than 24 hours. You can keep the potatoes from absorbing the water by making sure the water is not salted, and is chilled (you can even add ice to the water). To keep the potatoes from turning black from oxidation, add 1 teaspoon of lemon juice or white wine vinegar to a gallon of water.
McGee says that salt can help tenderize and soften vegetables by dissolving the vegetable's natural pectins, which may explain the minor textural differences between the beans with and without salt.
This turgor is caused by water within the cell pressing against the cell walls. If a potato dries out and loses moisture you will notice it turning soft, it's losing its turgor. Both the cells themselves and the cell walls play an important role in the texture and structure of a potato.
In the cooking process, the salty water forms a crust on the potato's skin and seals it which helps to prevent salt potatoes from tasting waterlogged as ordinary boiled potatoes sometimes do. As a result, salt potatoes have a unique texture that is similar to that of a baked potato.
Q: Why is it common to salt the exterior of a baked potato? A: Chefs started doing this years ago to allow the salt to absorb or draw out the moisture of the potato while baking, which results in a dry, fluffy potato.
Soaking potatoes in water helps remove excess starch. Excess starch can inhibit the potatoes from cooking evenly as well as creating a gummy or sticky texture on the outside of your potatoes. Cold water is used because hot water would react with the starch activating it, making it harder to separate from the potatoes.
As the potato is cooked its texture becomes softer and 'squishier'. The reason for the change in texture is the rupturing of the cell walls. When they are intact they hold the potato in a rigid shape. They are strong and hard to break just by gently pressing on the potato.
So, if a carrot is placed in very salty water, it will be less salty than the water around it. This causes the water in the carrot to move out of the carrot and into the salt water. The result is that the carrot becomes limp and tastes saltier than before.
Sometimes salt actually affects the cooking process, not just the flavor. It can help draw moisture out of sweating vegetables, softening them faster.
Salt Changes Things
How? The salt creates a higher ion concentration at the surface of the vegetable. Over time water travels from within the vegetables to the surface to create equilibrium. It's a process called osmosis.
A saltwater solution is hypertonic compared to the aqueous solution inside the cells. Therefore when the celery is placed in the saltwater solution water flows out of the celery, causing it to shrivel.
Takeaway. Saltwater is heavier than freshwater, so very light things will float in both. Heavy things will sink in both.
Salinity Affects Density
When salt is dissolved in fresh water, the density of the water increases because the mass of the water increases.
Because waxy potatoes are relatively low in starch and high in moisture, their cells stay intact when they're cooked, meaning that slices or cubes hold up when boiled or baked. Waxy potatoes will hold their shape when boiled—and dressed with a ton of cheese and pepper.
If you cook potatoes in water, it's likely they will become mushy after a while. To fix this and keep your potatoes intact, pour a little bit of vinegar (white, wine or cider) in cooking water. It works like magic! Don't forget to rinse your potatoes afterward.
Removing the starch reduces the carbohydrate content, which is helpful when you're following a low-carb diet. In addition, cooking high-starch potatoes makes them soft and crumbly. Remove the starch when you want to cook crispy potato dishes, such as chips, French fries or hash browns.
If the salt concentration in the cup is higher than inside the potato cells, water moves out of the potato into the cup. This leads to shrinkage of the potato cells, which explains why the potato strips get smaller in length and diameter.
The yolk emulsifies the water content and fat in the mashed potatoes to create a smooth and cohesive dish. As an added bonus, this addition of egg yolk makes your potatoes taste incredibly rich.
“The same boiling water that softens the potato, hardens the egg. It's what you're made of. Not the circumstances.” The message of this quote is that when a potato is boiled, it becomes soft but when an egg is boiled, the opposite happens!
Should potatoes be soaked before roasting? Yes! Soak the potatoes in cold water to remove the excess starch from the outside of the potato.