An improved process for tanning edible collagen food casings wherein the coagulated and washed collagen casing is exposed to a tanning bath which is free of aluminum chelating reagents and contains a mixture of aluminum ammonium sulfate, as A1NH4(SO4)2. 12H2O and monobasic aluminum sulfate (A10HSO4), the concentration of the aluminum ammonium sulfate in the bath being less than 3% by weight and the molar ratio of aluminum ammonium sulfate to monobasic aluminum sulfate being in the range of 1:2 to 2:1.
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