In 2015, an average U.S. dairy fluid milk plant processed 109.5 million pounds of milk. On average that same plant encountered an average product loss of 2.5%.
Product loss can happen throughout the entire process. Milk is left in the tanker or the lines during receiving. Losses occur during water-to-product and product-to-water interfaces during pasteurizing. Overfills contribute to produce lost in the filling area. Additional cost savings can be realized in wastewater reduction when this milk stops going down the drain.
Reducing losses in the receiving area is accomplished by water flushing raw milk lines from the receiving bays to raw storage silos with water given that an appropriate block and bleed valve arrangement controlled by optic sensors is in place. Per the Pasteurized Milk Ordinance (PMO), except when flushing lines with water, there needs to be sufficient separation between water piping and unpasteurized dairy products or lines used to transfer unpasteurized dairy products to prevent the accidental addition of water. A physical break, such as a swing elbow to a pipe connection or an arrangement of valves and piping in a block and bleed type configuration can be used. When challenged, the arrangement must demonstrate that it prevents the accidental addition of water when one or more of the valves fail.
Losses are reduced in pasteurization by water flushing milk source transfer lines in a similar manner. Optic sensors are also used on the discharge lines of the pasteurizer to determine water to product, product to water, and product to product transitions. Another important piece of instrumentation is the balance tank level sensor. It is important to lower the water level of the balance tank to a minimum level during transitions to reduce the amount of interface between water and product.
In the filling area, losses are reduced by water flushing from pasteurized silos to fillers and tankers with pasteurized water or Pasteurized Equivalent Water (PEW). The PMO accepts pushing pasteurized products with water that has undergone a process equivalent to pasteurization that has been found acceptable to FDA and the State Regulatory Authority. Overfills are minimized by maintaining a constant level in the filler bowl allowing for the consistent filling of containers. Statistical Process Control (SPC) software is used to historically track filled containers based on weight.
There is another area of the process where loss is far more subtle. Many fluid milk plants utilize milk standardization systems. These systems are installed after separation of the raw milk into skim and cream and prior to pasteurization and homogenization. These systems allow the operator to produce skim, 1%, 2%, and homogenized milk on-the-fly. Depending on the accuracy and precision of the existing milk standardization system, it is possible that product losses are occurring by producing products that do not meet regulatory and company specifications. This could occur by giving away more butterfat or solids-not-fat (SNF) than is required for a specific product. This also reduces the amount of excess cream, a by-product of standardization that is sold and used to create other products such as ice cream or butter.
Another factor affecting milk standardization systems is its integration with the milk separator, pasteurizer, and other process equipment. A system which is not integrated delays in recovering after a process disturbance such as a separator discharge. This leads to periods of producing product out of specification, while the milk standardization system recovers. An integrated system anticipates these disturbances and freezes control devices prior to, during, and for a period after, and then releases the control devices back to automatic control.
By ensuring the maximum amount of milk entering a plant is processed and sold, and a minimum amount is sent to the drain as wastewater, a facility can expect to minimize their fat loss. While achieving 0% fat loss may seem impossible, based on my experiences, it is possible for them to reduce their fat loss to around 1% when implementing the solutions described in this article. I would be happy to answer any questions you have on these solutions. Leave me a comment below.