Staling, or "going stale", is a chemical and physical process in bread

Bread

Bread is a staple food prepared by cooking a dough of flour and water and often additional ingredients. Doughs are usually baked, but in some cuisines breads are steamed , fried , or baked on an unoiled frying pan . It may be leavened or unleavened...

 and other foods that reduces their palatability. Stale bread is dry and leathery.

Mechanism and effects

Staling is not, as is commonly believed, simply a drying-out

Desiccation

Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

 process due to evaporation

Evaporation

Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

. Bread will stale even in a moist environment, and stales most rapidly at temperatures just above freezing. Bread stored in the refrigerator will have increased staling rates and should therefore be kept at room temperature. However, refrigeration delays the growth of mold and extends the shelf life of bread.

Although the precise mechanism of staling is still unknown, one important mechanism appears to be migration of moisture from the starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 granules into the interstitial spaces, degelatinizing

Retrogradation (starch)

Retrogradation is a reaction that takes place in gelatinized starch when the amylose and amylopectin chains realign themselves, causing the liquid to gel....

 the starch. The starch amylose

Amylose

Amylose is a linear polymer made up of D-glucose units.This polysaccharide is one of the two components of starch, making up approximately 2-30% of the structure...

 and amylopectine molecules realign themselves causing recrystalisation. This results in stale bread's leathery, hard texture.
Additionally, pleasant "fresh" flavor is lost to the air, and often unpleasant flavor is absorbed from it as well, especially in a confined space with other food such as a refrigerator

Refrigerator

A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...

.

Countermeasures

Anti-staling agents used in bread are fatty acid

Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

s as monoglyceride

Monoglyceride

A monoglyceride, more correctly known as a monoacylglycerol, is a glyceride consisting of one fatty acid chain covalently bonded to a glycerol molecule through an ester linkage....

 and diglyceride

Diglyceride

A diglyceride, or a diacylglycerol , is a glyceride consisting of two fatty acid chains covalently bonded to a glycerol molecule through ester linkages....

 and wheat gluten

Wheat gluten

Wheat gluten can refer to:* The gluten found in wheat, a sticky substance composed of the proteins gliadin and glutenin* Wheat gluten , a food prepared from these proteins, such as seitan or wheatmeat...

.

Culinary uses

Specifically stale bread is an important ingredient

Ingredient

An ingredient is a substance that forms part of a mixture . For example, in cooking, recipes specify which ingredients are used to prepare a specific dish. Many commercial products contain a secret ingredient that is purported to make them better than competing products...

 in many dish

Cooking

Cooking is the process of preparing food by use of heat. Cooking techniques and ingredients vary widely across the world, reflecting unique environmental, economic, and cultural traditions. Cooks themselves also vary widely in skill and training...

es, some of which were invented for the express purpose of using up otherwise unpalatable stale bread. Examples include bread pudding

Bread pudding

Bread pudding is a bread-based dessert popular in many countries' cuisine, including that of Great Britain, France, Belgium, Puerto Rico, Mexico, Malta, Argentina, Louisiana Creole, and the southern United States...

, bread sauce

Bread sauce

A bread sauce is a warm or cold sauce thickened with bread. It is a savoury sauce served with a main meal.The sole survivor of the medieval bread-thickened sauces, the traditional British bread sauce is made with milk, butter or cream, and bread crumbs, flavoured with onion, salt, cloves, mace,...

, skordalia

Skordalia

Skordalia or skordhalia/skorthalia is a thick puree in Greek cuisine made by combining crushed garlic with a bulky base—which may be a purée of potatoes, walnuts, almonds, or liquid-soaked stale bread—and then beating in olive oil to make a smooth emulsion. Vinegar is often added...

, garbure

Garbure

Garbure is a thick French soup or stew of ham with cabbage and other vegetables, usually with cheese and stale bread added. The name derives from the use of the term garb to describe sheaves of grain depicted on a heraldic shield or coat of arms. Thus the name of garbure, which is eaten with a...

, fondue

Fondue

Fondue is a Swiss dish of melted cheese served in a communal pot over a spirit lamp , and eaten by dipping long-stemmed forks with bread into the cheese...

, crouton

Crouton

A crouton is a small piece of sautéed or rebaked bread, often cubed and seasoned, that is used to add texture and flavor to salads, notably the Caesar salad, as an accompaniment to soups, or eaten as a snack food. The word crouton is derived from the French croûton, itself derived from croûte,...

s, haslet

Haslet

Haslet, also spelt 'Acelet', is a pork meatloaf with herbs originally from Lincolnshire, England. The name is derived from the Old French hastilles meaning entrails ....

, gazpacho

Gazpacho

Gazpacho is a cold Spanish/Portuguese tomato-based raw vegetable soup, originating in the southern region of Andalucía. Gazpacho is widely consumed throughout Spain, neighboring Portugal and parts of Latin America...

, wodzionka

Wodzionka

Wodzionka or brołtzupa is the Silesian bread or water soup made from stale bread, fat, and water. Traditionally, wodzionka is prepared by soaking two- to three-day old stale bread in water or broth and adding garlic, bay leaves, pepper and other seasonings, fried bacon, and lard or butter...

, french toast

French toast

French toast or Eggy Bread, is a food made with bread and eggs. It is a Christmas time dessert in Portugal and Brazil.Where French toast is served as a sweet dish, milk, sugar, or cinnamon are also commonly added before frying, and it may be then topped with sugar, butter, fruit, syrup, or other...

, bread dumplings and flummadiddle

Flummadiddle

Flummadiddle is a baked main course pudding consisting of stale bread, pork fat, molasses, and spices including cinnamon, allspice, and cloves. It was a part of early American cuisine, especially of New England fishermen.- References :...

.

In medieval cuisine

Medieval cuisine

Medieval cuisine includes the foods, eating habits, and cooking methods of various European cultures during the Middle Ages, a period roughly dating from the 5th to the 16th century...

, slices of stale bread, called trencher

Trencher (tableware)

A trencher is a type of tableware, commonly used in medieval cuisine. A trencher was originally a piece of stale bread, cut into a square shape by a carver, and used as a plate, upon which the food could be placed before being eaten. At the end of the meal, the trencher could be eaten with sauce,...

s, were used instead of plates.

Destaling

Stale bread can be partially destaled by heating to 60 °C (140 °F) in a conventional oven or microwave oven

Microwave oven

A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...

. This re-gelatinizes

Starch gelatinization

Starch gelatinization is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites to engage more water. This irreversibly dissolves the starch granule...

the starch granules. However if not eaten before it cools or dries, the bread is even worse than before due to the moisture loss.