1. A method for operating one or more bulk product blending and packaging plants in a manner that moves operations of a given plant, or a given collection of plants, toward an optimum for a performance metric during a designated time horizon comprising one or more time intervals under operating constraints and physical and/or economical limitations, each such plant comprising blending equipment, at least one storage tank, packaging equipment, one or more packaged product storage facilities and unloading and discharging facilities, wherein said method comprises the following steps: (I) a computer implemented step of receiving a data set comprising: (a) data identifying a time horizon comprising one or more time intervals; (b) data identifying blending equipment and one or more operational parameters thereof; (c) data identifying at least one storage tank and one or more operational parameters thereof; (d) data identifying packaging equipment and one or more operational parameters thereof; (e) data identifying packaged product storage facilities and one or more operational parameters thereof; (f) data identifying unloading and discharging facilities and one or more operational parameters thereof; (g) data relating to the interconnections between plant equipment; and (h) data relating to historical demand for each packaged product; (II) a computer implemented step of using the data set to populate model parameters of a mixed-integer non-linear mathematical optimization model constructed to mathematically describe the operations of the blending and packaging plant(s); wherein the model comprises model parameters, decision variables, constraints, and an objective function; wherein the decision variables represent quantitative decisions to be made in each interval regarding plant capacity as a function of one or more of the following: number of production equipment, number of workers, production shift structure, overtime, number of product changeovers and setup time required to complete a product changeover; wherein additional decision variables are quantitative decisions to be made in each interval regarding plant production and inventory; wherein the constraints comprise: (a) one or more terms limiting availability and capacity of the blending equipment; (b) one or more terms limiting availability and capacity of the at least one storage tank; (c) one or more terms limiting availability and capacity of the packaging equipment; (d) one or more terms limiting availability and capacity of the packaged product storage facilities; (e) one or more terms limiting availability and capacity of the unloading and discharging facilities; (f) one or more non-linear terms relating number of batches of each packaged product to product batch size; and (g) one or more non-linear terms relating the size of each batch of packaged products to quantity of safety stock required for the product; wherein the objective function is a performance metric: (III) a computer implemented step of running an algorithmic solver to obtain a solution to the mixed-integer non-linear mathematical optimization model; and (IV) operating the plant(s) substantially according to the solution obtained or according to an operating plan made based on the solution obtained.