Silage is fish, or parts of fish, that are mixed with a preservative to improve the durability. Normally the acid is used to lower the pH levels to a level where germ growth stops. Most used acid is formic acid.

When the temperature is above 5º C and the pH levels are between 3,5 and 4,5, the fish mass starts to tear down and this happens faster if the temperature is higher, up to 40º C. This is also called autolysis, because of the automatic continuation with two enzymes that naturally are a part of the fish mass. The enzymes tear down the muscular tissue and the fish mass becomes a liquid.