Re: Why are some foods stickier than others?

Since the mother is directing the question, I'll answer to her instead of 
the child:

Foods are sticky which stick to your fingers or to tableware materials 
(steel, china, glass). 

Most sticky foods have stickiness based on their desire to attach to 
water. This means that sugars and proteins are sticky once they get water 
mixed in with them the right way.

Some sugars are sticky because they are very soluble in water and are 
hungry for more. This include table sugar and corn syrup sugars.

Some proteins like water and some don't. The ones that like water are 
sticky; the ones that like fats instead are not.

Starches and gums are polymers of sugars and typically also love to mix 
with water. Starch and gum solutions are also quite sticky.

Oil and water don't mix, so fats are generally not called sticky, although 
solid fats are greasy and hard to get off surfaces, since they flow easily 
to coat them under force. 

Most glues are made from water and proteins, which can be made very 
sticky. Others are made from starch or sugar pastes or from solutions of 
gums.

Peanut butter seems very sticky for two reasons. The first is that it's 50% fat, 
which is greasy and hard to remove. Secondly there is a lot of protein and 
sugar in peanut butter with very little water.

Some materials are also called sticky which stick to themselves. The is 
the case with peanut butter.

An interesting experiment is to mix some water and flour to make a stiff 
dough. If you use more water, it gets very sticky. If you then mix in a 
lot of fat (oil), it becomes no longer sticky. This shows very clearly the 
relation between water and stickiness. Flour proteins generally prefer to 
interact with fat than with water.