 The recovered beef material is extruded through long tubes that are thinner than a pencil , during which time at the Beef Products , Inc . ( BPI ) processing plant , the meat is exposed to gaseous ammonia . At Cargill Meat Solutions , citric acid is used to kill bacteria such as E. coli and Salmonella . Gaseous ammonia in contact with the water in the meat produces ammonium hydroxide . The ammonia sharply increases the pH and damages microscopic organisms , the freezing causes ice crystals to form and puncture the organisms ' weakened cell walls , and the mechanical stress destroys the organisms altogether . The product is finely ground , compressed into pellets or blocks , flash frozen and then shipped for use as an additive . 
