Many foods—sauces, soups, desserts a.o.—require thickening. Thickening keeps flavoring ingredients suspended and improves flavor, texture and looks. Some thickening methods are listed below:
Reducing (simmering down): e.g. tomato sauce, cream-based sauces.
Emulsifiers do the same thing for oily foods.
Food gums are added to hot or cold or hot liquid, e.g. gelatin, pectin, agar, guar,….
Blending / pureeing: solid foods are blended into a sauce/soup.
Dry ingredients absorb liquid and thicken the liquid, e.g. bread / pasta / tapioca / chia seeds.
Cooking rice and beans has the same effect.
Stewing: cooking may partially liquefy some solids. (e.g. applesauce)
Eggs / cream:
Emulsions: oils can be emulsified into egg yolks.
Whole eggs, egg yolks and/or egg whites can be used to thicken sauces and soups.
Egg whites and cream can be beaten into a stiff foam that can be used to thicken foods.
Combinations of any of the above.