Chemically, why does water make hard foods soft?

Answer 1

I think water makes foods "soft" due to the effects of hydrogen bonding. Water is a polar molecule with hydrogens and oxygens. Because oxygen is electronegative, it hogs all the electrons from the hydrogen, making the oxygen more negative and the hydrogens more positive.

This in turn leads the oxygen to want to bond to positive things and hydrogen to negative things. When you put foods in water, the polarity of the water molecule will cause bonding with the molecules of the foods and cause them to break apart.

Hope that helps.

Answer 2

Water doesn't "chemically" make hard foods soft. This is a physical phenomena. The food nor the water are reacting, and you could dehydrate the food and have exactly the same water you with which you started.

You are in reality disolving starches, sugars in water. If you have enough water and a little agitation, you'll disolve the food completely as opposed to "softening" it. In reality you're solvating into solution.

Answer 3

The chains of starch molecules in foods like rice and pasta have little gaps between them like the holes in a sponge and water can get into these gaps. Just like a sponge softens when it holds water so do the chains of starch molecules in food.
Eventually the chains of starch themselves will break down and the starch will go into solution. That's why you don't want to overcook your pasta or rice.