Physical Changes in Food

Unlike chemical changes, physical changes in foods do not result in the formation of new compounds. A few of the common physical changes occurring in foods as they spoil are evaporation, drip loss, and separation. Water evaporates out of improperly stored foods, creating an unattractive, dried-out appearance and possible undesirable flavor changes. Water can also be lost (syneresis) out of foods such as gelatins, yoghurt, and sour cream as they age. Separation of water and oil occurs in such foods as non-homogenized milk, mayonnaise, salad dressings, and high-moisture cheeses when they are stored too long or are frozen and then thawed. This separation is the reason why sandwiches spread with mayonnaise or made with high-moisture cheeses do not freeze well.