The “boiling” phenomenon in formic acid preserved poultry by-products

Summary

In Norway, poultry by-products (viscera, heads, feet) used as ingredient in fur animal feed are preserved with formic acid at pH 3.5-3.8 to prevent bacterial growth.. The preserved product is semi-liquid (app. 25 C) and is transported in tank trucks to the fur animal feed producers. Occasionally, the mass expands and runs over the tanks during transport and may continue running over after being loaded to storage tanks. Typical signs of this so called “boiling” phenomena, are bubbles and foaming similar to boiling, indicating the occurrence of gas production the mass. The over-running may last for 1-3 days and it appears to terminate by it self. Similar problems with overrunning have been reported with fish silage preserved with formic acid. The economic cost of this phenomenon is related to extra clean-up work and in some cases loss due to destruction of the product. The main objective of the present experiment was to identify causes for the so-called “boiling” cases, i.e. gas –production during storage and transport of acid stabilised poultry by-products. This was obtained by carrying out small scale laboratory storage trials on freshly preserved raw material in combination with volumetric measurements of gas production, chemical gas analysis and microbial analysis. In addition trials were carried out to test the inhibitory effect of gas-production by a sodium bisulphite, which in earlier studies has shown to have a possible inhibitory effect on gas-production.