This is quite easy and straight forward, but takes some extra work. The first batch received is documented with a batch or parcel number and a receipt date. The quality of the product is also documented. If the tank is not empty and the next batch is received on top of the remains of the previous one, then the whole contents is considered a new batch, since both batches mix in the tank and a new quality specification is "born" due to the mixing of the two tanks. For the whole of the new tank contents the quality is recalculated and documented in a Tank Composition List. This recalculation of the quality of the new batch created is confirmed by taking a sample after tank homogenisation and an analysis of the quality parameters. This process is repeatedly done for each new batch received. This way one keeps track of each batch received, new new quality in the tank after receipt of each batch and a chronological traceability of each batch received. Other companies operate a procedure that a tank is considered "empty" if the volume of the product inside is less than 2% of the tank capacity, this way one can start with a "fresh" tank composition list. Also, a a tank requires regular maintenance and inspection, the interior wall and bottom thickness is also verified with certain intervals, the tank has then to be empty. Also this is a moment to re-start the tank composition. The only disadvantage is that once in the tank, the combined batches form one new batch once these are stored together in one tank, this increases the size of a product recall should one of the batches be out of spec or not meeting food safety requirements. However, this is only an issue if there is a product safety issue with one of the batches. Hope this all helps.