A mixing apparatus (1) for mixing slaughter offal with a preservative agent, the apparatus comprising an offal collection tank (3) with a bottom (4) provided with a discharge opening (5) connectable to a closable discharge, an agitator (8) extending into the offal collection tank, and a pump unit (9) operatively connectable to the discharge, wherein the apparatus further comprises a preservative reservoir (7) mounted on top of the collection tank (3). A collection and preservation system is provided, wherein the addition of preservation agent can be strictly controlled, can easily and quickly be installed and connected when it is to be used. After use, the system is easily removed and cleaned.