Crisp bread (Swedish: knäckebröd, spisbröd or hårdbröd, Finnish: näkkileipä) is a very flat and dry Nordic type of bread, containing mostly rye flour.
According to some sources, crisp bread is more than a thousand years old and was a staple of the Vikings on their raids, and as ship biscuit would keep for several months. Traditional crisp bread was invented about 500 years ago and consists of wholemeal rye flour, salt and water. Today, however, much crisp bread contains wheat flour, spices and grains, and is often leavened with yeast or sourdough.
Crisp bread contains a large amount of air. In the case of unleavened crisp bread, bubbles are introduced into the dough mechanically. Traditionally, this was done by mixing crushed ice into the dough, which then evaporated during baking. Today, the dough, which must contain a large amount of water, is cooled and mixed until bubbly. Another method is to knead the dough under pressure in an extruder. The sudden drop in pressure then causes water to evaporate, creating bubbles in the dough.
Crisp bread is only baked for a few minutes, at temperatures usually not exceeding 100 °C.