A great explanation about molecular cuisine and the mystery of Coleslaw by Richard David Feinman PhD

Coleslaw
A salad of finely shredded raw cabbage and sometimes shredded carrots, dressed with mayonnaise (white slaw) or a vinaigrette (red slaw).

The problem:

Here's a culinary thermodynamics question. In chemistry, we want to know whether a chemical reaction is spontaneous, that is, goes by itself without addition of energy. It used to be thought that if a reaction gives off heat it will be spontaneous. This is obviously true of many reactions. In particular, combustion reactions, in the furnace or in the body, generate a lot of heat and generate energy for work as well. It isn't always true, however.

Now, the key steps in making coleslaw are first to finely shred the cabbage and then to salt it until it begins to lose water. Then squeeze out as much water as possible so that when you add mayonnaise, it doesn't become soggy. If you do this -- for the experiment, use a cabbage that is at room temperature -- you will find that when you go to squeeze out the water, the cabbage is palpably very cold but the reaction goes by itself. 

Why? And why, if you don't do this, does the water come out when you add the mayonnaise and become soggy?

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   FB user Is it something to do with the way you use rock salt to make ice cream?

  
  
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  Richard David Feinman First, there are two variables in thermo: energy (heat and work) and entropy (structure or organization or "probability"). Chemical reactions will go by themselves if the energy decreases (heat given off) or if the entropy increases (looser structure, higher probability arrangement) or, more precisely, if a combination of the energy and entropy (the Free Energy) goes down.
  
  Now, vegetables have a large amount of water. It is part of the cellular and extracellular structure. Water forms associations with the stuff in the cell, the cell membranes which have cellulose and other carbohydrates. So, internally, vegetables have a lot of organization held together, in part, by the chemical association (hydrogen bonds) between water and the cellular and fibre components of the vegetable (hydrophilic force). if you add salt to the vegetable, it will draw some of the water out of the vegetable. Now there are two forces: water-vegetable, water-salt. Which wins? Neither really wins. The entropy wins. Salt water has much greater entropy (less structure) than the plant material. The reaction is driven in the direction of breakdown and release of water. The system will extract whatever heat is needed to break enough bonds to get the right water-vegetable equilibrium. Both energy and entropy are involved but, in this case, the reaction is substantially entropically driven.
  
  If you don't do this, when you add mayonnaise, the system may stay together as a mixture -- not my favorite kind of Cole slaw but some prefer the crunch of cabbage -- but not always. There is another force called the hyrophobic force (really the lack of hydrophilic force) which is what makes water and oil not mix. Now, the hydrophobic mayonnaise comes in contact with the structured cabbage and the incompatibility plus the entropy will allow the water to separate and the Cole slaw becomes soggy -- nobody's favorite kind of Cole slaw.

  
  
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  Richard David Feinman In the case of rock salt for ice cream, it is that the ice-salt mixture is stable at a lower temperature, so good for keeping the ice cream cold. Same reason you salt the ice on your sidewalk (takes less heat to melt the ice mixture).

So when you salt a raw veggie, for instance, fennel, radish, kale, water goes out and the temperature of the veggie decreases as you increase the entropy of the system so it uses whatever energy to increase entropy and the temperature of the veggie decreases.