Altbacken vs. abgestanden vs. alt
In German, translating the concept of "stale" or "no longer fresh" requires choosing a specific word based on the type of food or drink being described. The words altbacken, abgestanden, and alt all describe things that have lost their freshness, but they apply to entirely different categories, such as baked goods, liquids, or general food items.
Altbacken
The word altbacken specifically translates to "stale" when referring to baked goods that have become dry and hard. It literally means "old-baked" and is used almost exclusively for items like bread, rolls, pastries, and cakes, though it can also be used figuratively to describe old-fashioned ideas or clothing.
Wir können aus dem Brot Paniermehl machen, da es schon ziemlich altbacken ist.
(We can make breadcrumbs out of the bread since it is already quite stale.)
Ich esse nicht gerne altbackene Brötchen zum Frühstück.
(I do not like eating stale rolls for breakfast.)
Der Bäcker verkauft altbackenen Kuchen zu einem günstigeren Preis.
(The baker sells stale cake at a lower price.)
Diese Kekse schmecken etwas altbacken, weil die Packung offen war.
(These cookies taste a bit stale because the package was open.)
Abgestanden
The word abgestanden translates to "stale" or "flat" and is used for liquids and air that have lost their freshness by sitting untouched for too long. You must use this word to describe things like water that has been left out, beer or soda that has lost its carbonation, or the stuffy air in an unventilated room.
Niemand trinkt gerne abgestandenes Bier ohne Schaum.
(No one likes drinking stale beer without a head.)
Das Wasser in dieser Flasche schmeckt völlig abgestanden.
(The water in this bottle tastes completely stale.)
Nach dem langen Urlaub war die Luft in der Wohnung sehr abgestanden.
(After the long vacation, the air in the apartment was very stale.)
Lass den Kaffee nicht ewig auf dem Tisch stehen, sonst wird er kalt und abgestanden.
(Do not leave the coffee sitting on the table forever, otherwise it will become cold and stale.)
Alt
The word alt simply means "old" and is the most general term used to describe food that is no longer fresh, close to spoiling, or past its expiration date. While it can be used for bread as a simpler synonym for altbacken, it applies broadly to all types of groceries, such as aging cheese, old meat, or wilting vegetables.
Wirf das Fleisch besser in den Müll, es ist schon zu alt.
(You had better throw the meat in the trash, it is already too old.)
Meine Großmutter macht einen leckeren Auflauf aus altem Gemüse.
(My grandmother makes a delicious casserole out of old vegetables.)
Dieser alte Käse riecht viel strenger als der frische Käse aus dem Supermarkt.
(This old cheese smells much stronger than the fresh cheese from the supermarket.)
Hast du noch altes Brot für die Enten am See?
(Do you still have old bread for the ducks at the lake?)
Summary
To sound natural in German, categorize your stale items before choosing your word. Use altbacken for bakery items that have gone dry, abgestanden for liquids that have gone flat or air that has become stuffy, and alt as a versatile term for any food that is simply old or past its prime.