Bulk Milk Tank wash program assessment
Almost all new bulk milk tanks sold since the mid-1990s have automatic cleaning systems. The degree of flexibility to adjust the wash program varies enormously between brands and between models within a brand. Often the wash programs are coded (similar to that on automatic wash controllers for milking machines) and may require a service technician to make adjustments.
The wash program for a bulk milk tank should follow the same principles as for cleaning milking machines. The program must include a pre-rinse, a wash, and a final rinse. The same requirements for water quality apply, although greater attention is required to ensure the water is free of suspended solids as these can block filters/strainers and spray heads.
There are two factors specific to cleaning bulk milk tanks that will influence the wash program. These are:
- Rinse requirements: After the milk has been emptied the milk contact surface inside the vat is cold. The milk residues are also cold and they will require greater effort to remove (compared to when they are at body temperature). Milk foam may be present and will also need removing. To minimise the risk of damage to the evaporator plates (on the other side of the milk contact surface) sudden changes in temperature are discouraged by vat manufacturers. To accommodate these conditions, the rinsing procedure is often different to that used for milking machines. There often are two rinses; the first is cold and its role is predominantly to remove the milk foam as well as the milk residue. The quantity of water used may be greater for this cycle. A second rinse is usually warm, it further removes milk residues and helps to raise the temperature of the milk contact surfaces in preparation for the subsequent hot wash. Some wash programs may combine the two rinse actions into one; i.e. the first part of the rinse uses water at ambient temperature which progressively becomes warmer.
- Temperature limitations: Again, to minimise risks of damage to evaporator plates, manufacturers place a maximum water temperature of 70 oC for cleaning inside the vat. This can affect the approach to sanitisation and the types of detergents used. Most vats source their hot water from a dedicated domestic main pressure hot water service (HWS). These typically have a maximum heating temperature of 70oC. Operating at lower temperatures may require higher dose rates of chemicals to be used.
Experience from the field has found that the wash programs (number of cycles, temperature of each cycle, cycle volume, and contact time) vary considerably among bulk milk tanks. The Table below provides an example of the type of wash program that may be encountered. It is important to note that wash programs for bulk milk tanks do vary (e.g. some may perform three cycles, or four cycles).
|1st cycle – pre-rinse||Cold rinse, single pass||The temperature of the water may be gradually increased to ~35-40°C. Cycle volume ~2% of tank capacity. This is sometimes increased when excessive milk foam is present|
|2nd cycle – wash||Hot wash. Alernating alkali/acid (pick-up/pick-up), 60-65°C (starting temp), recirculate for 5-10 mins then discarded||Some systems may only perform a hot alkali wash. The acid function is incorporated into the sanitising cycle. The number of chemical dosing pumps may indicate the wash programs possible. For example, three dosing pumps may indicate alternating alkali/acid wash and a chemical sanitising rinse. Cycle volume ~1-2% of vat capacity|
|3rd cycle – intermediate rinse||Cold rinse, single pass||Cycle volume ~1% of vat capacity|
|4th cycle – sanitising rince||Sanitising/acid sanitising rinse. Recirculate 4-6 mins then discard||Temperature may be adjustable on some systems. Cycle volume ~1-2% of vat capacity|
|5th cycle – final rinse||Cold rinse, single pass||Cycle volume ~1% of vat capacity|
Although the wash program characteristics for bulk milk tanks can be different to the wash programs for milking machines the six principles of cleaning still apply.
Complete the details for each cycle to determine whether all the essential steps are being covered. Use this assessment to uncover and then correct the discrepancies.