Milking parlours may have become larger and more automated, but the principles of plant cleaning have remained largely unaltered since the development of milking parlours. Effective plant cleaning relies on an adequate volume of water, at the right temperature with the correct concentration of sanitising chemicals.
Poor plant cleaning will often result in a high bacterial count in the milk, although there can be other contributory factors such as the inside and outside of the udder.
A recommended plant cleaning routine
After milking, thoroughly brush clean the outside surfaces of the clusters and attach to clean jetters. Pay particular attention to the contact surfaces between the jetters and clusters. Ensure that any in-line mastitis detectors are clean, as any debris or clots will interfere with the flow of wash solution.
Remove the milk filters and rinse clean prior to re-attaching. Where cotton milk filters are used, replace with new filters. Don’t forget to check if there are any particular problems such as mastitis clots or heavy contamination and act on the information.
Allow a minimum of 14 litres per cluster of cold, but preferably tepid, water for the pre-rinse. The purpose of this pre-rinse is to remove the majority of milk residues from the plant. When assessing how much water is required do not forget to include any reject milk clusters that are included in the wash system. Run the pre-rinse water through the system and discharge to waste.
For the circulated main wash also allow a minimum of 14 litres of hot water (85ºC) per unit – unless stated otherwise by the manufacturer of the detergent disinfectant/sanitiser. To warm up the plant, discharge around 4 litres per unit to waste. The temperature of the final discharge water immediately before returning the delivery pipe to the wash trough should be at least 55ºC.
At this stage add the correct amount of detergent-disinfectant/sanitiser to the wash trough. To add prior to this stage is uneconomic and of doubtful benefit.
Circulate the main wash for 5 – 7 minutes, unless stated otherwise by the manufacturer of the chemical being used. The temperature of the circulated wash solution should be at least 55ºC at the end of the cycle.
Follow with a final rinse of cold water at 14 litres per unit. Consider adding sodium hypochlorite to the final rinse water at the rate of 25ml per 40 litres, or peracetic acid (typically at the rate of 0.01 – 0.02% (4 – 8ml per 40 litres)). There may be a requirement to add these chemicals to the final rinse if water quality is poor.
Although the above applies to manual plant cleaning, the same considerations apply to automatic plant cleaners. Some systems provide two pre-rinses, the first using cold water and the second warm/hot water to heat up the plant. In the latter case no water maybe discharged to waste at the start of the hot circulation wash. There may also be two post-rinses, the first will be clean cold water with sodium hypochlorite or peracetic acid added to the second.
Whether manual or automatic plant cleaning it is important that you regularly check the volumes and temperatures of water and the amount of all chemicals used. However, do take full health and safety precautions when handling or measuring plant sanitising products.
Finally, do periodically observe the main wash. Check that there is adequate distribution of wash water to each cluster and with recorder jar plants that there is a good distribution between the jars and clusters. Also, with jar systems ensure that there is not intermittent flooding and starvation in the recorder jars.
With direct to pipeline milking systems the milk lines are of a much larger diameter to recorder jar plants. To ensure that the whole of the inside of the pipeline is cleaned air injection is required to help create a slug of water that scours the internal surfaces. It is crucial that the slug formed maintains its integrity along the complete length of the pipeline until it enters the receiver vessel.
If the period of the air injection is too short the slug is not correctly formed. Conversely, if it is too long the vacuum level in the plant will fall sharply and the slug of wash water will break down and the solution flow rates will fall. In either case circulation of plant cleaning wash water is compromised
The slug needs to travel at around 8 – 10 metres per second, which broadly translates into one second of air injection for every 10 metres of milkline. There also needs to be an interval without air injection for the milkline to start filling with wash water, and will typically be around 30 seconds. As a rule of thumb there should be at least 15 wash slugs per wash cycle.
Milking machine manufacturers have developed various design features to ensure the correct formation of the slug, but it is important that the duration of the air injection and the interval between slugs are optimised and checked. If wash solution is seen and felt to hit the receiver vessel after the air injection, then the integrity of the slug has been maintained and the milkline correctly scoured. However, if the slug of solution is not correctly formed, the upper surfaces of the milkline will not clean satisfactorily.
Finally, do periodically check if the plant is cleaning properly. Inspect liner mouthpieces, the internal surfaces of the milk meters, the inside of receiver vessels (not always possible), the ball of the sanitary trap and even the long milk tubes.
And of course, with automatic plant cleaning systems, make sure that there is sufficient chemical in the drum!