Zwieback originates from East Prussia. Somewhat later, it was introduced in Russia from where it was brought to North America during the Russian Revolution. Today, zwieback is available in a number of varieties and is often given to patients with stomach troubles as a solid meal since it is easy to digest. The name zwie (twice) -back” (baked) refers to the way zwieback is made.
From Wikipedia: “Zwieback is a form of rusk eaten in Scandinavia, Germany, Austria, France, Switzerland, Italy, Slovenia, and Greece. It is a type of crisp, sweetened bread, made with eggs and baked twice. ...
Zwieback is commonly used to feed teething children and as the first solid food for patients with an upset stomach.
The name comes from German zwei ("two") or zwie ("twi-"), and backen, meaning "to bake". Zwieback hence literally translates to "twice-baked". The French and Italian names, respectively, biscotte and fette biscottate have the same origin, biscotto (biscuit), which also means twʼice ("bis-") baked (-"cotto").”
“First, a sweet bread similar to white bread is prepared and baked. This is called the “Einback” (once baked). The dough contains high gluten flour (for example, type 550), milk, butter or margarine, sugar, eggs, yeast, and salt. Zwieback sold in stores for children and other household members contains about 6 parts fat and 10 parts sugar for every 100 parts flour. In addition, other types of flour such as spelt flour and whole grain flour (for whole grain zwieback) and other ingredients for special types of zwieback are used. See the section ʽTypes.ʼ
After baking, the “Einback” is cut into slices and roasted in the oven on low heat. It takes on color, dries out, and becomes crispy — the result is zwieback. When zwieback is sold fresh, a relatively high moisture level is permitted and the center may still be soft. If it is to be stored for a longer period of time, it has to be dried in the oven or drying chamber for an additional period of time in order to reduce the water content to 10% or lower. The crumbs immediately become crisp. Before roasting, the “Einback,” can be spread with a mixture such as a chestnut spread or frosted. Other coatings (e.g., couverture) are added after roasting.*”
Note about packaging requirements:
“Zwieback usually has a long shelf life, but it does easily absorb moisture and can then lose its crispness and spoil more easily. There is also the danger that the fat content will become rancid from exposure to air and light. It is therefore essential that the packaging protect zwieback from water vapors, air, and light.*”
“There have always been a number of types of zwieback to choose from. Here are a few examples:
Note (italics): * = Translation from a German Wikipedia entry