Thursday, 19 September 2019 13:55

Keep your dairy spotless

Written by  Staff Reporters

DairyNZ emphasises that the cleanliness of the milking system and the dairy is critical.

The New Zealand Food Safety Authority has strict guidelines about cleaning to maintain milk quality standards.

Correct cleaning maintains milk quality. So devise a process to ensure cleaning is done properly to remove all residues and destroy all bacteria. 

Safety issues must also be considered.

Cleaning must be done properly as bacteria can build up in the plant and contaminate milk. The bacteria affect milk quality by breaking down the components in milk. This reduces the shelf life of milk and milk products, and produces ‘off’ flavours in cheeses and milk powders.

Bacteria can enter the plant from cows (teat skin and infected udders) and the environment (drawn into the cluster). 

The milking environment is ideal for bacterial growth. 

Effective machine cleaning will control the presence of bacteria in the plant. The quality of the water used is very important in achieving a successful clean.

There are four key elements of the cleaning process: thermal, time, kinetic energy and chemical energy.


Water which is not hot enough leads to redepositing of the milk residues removed, and water which is too hot denatures protein, breaks down detergents and damages seals and rubberware.

Aim for a temperature of 80-85°C as water exits the hot water storage cylinder.

Hot water washes should be dumped when wash water temperature falls below 55°C.


Hot water must contact the surface for a minimum of four minutes; this should be extended to seven minutes by re-circulating during an alkali wash. Pre-heating the plant will help achieve at least five minutes of contact time at the recommended temperature.

For the milking plant, 10 litres of hot water per cluster is recommended to achieve sufficient contact time.

For the bulk milk tank, hot water should be a minimum of 2% of the bulk milk capacity or 120 litres for 5700 litre tanks or smaller.

Kinetic energy

Air injectors and a reservoir of water at the end of the milk line can create a slug formation for cleaning the top of the milk line.

Small flushing pulsators used to induce turbulence are largely ineffective. Instead you may need to do regular brushing or use a large flushing pulsator/air injector.

Milk lines generally require turbulence created via an effective flushing pulsator to fill the line and clean the milk line or some alternate effective cleaning system.

Chemical energy

Acid detergents remove mineral deposits. They can be used in hot or cold water but are more effective in hot water. Acid sanitisers commonly incorporate chemicals which also kill bacteria. These sanitisers are intended to stay in the plant after washing to provide extended protection. Acid sanitisers should always be added to the final wash.

Alkaline detergents remove fat and protein. If left in the plant, they can cause damage to rubberware so they must be followed with an acid wash to neutralise the alkali and leave the plant sanitised. The alkaline detergent is almost always chlorinated, or chlorine added.

Plant cleaning routines

As a minimum the following steps are necessary:

• Cold water rinse after every milking

• An acid wash after every milking

• An alkali wash at least twice weekly

• An acid rinse after every alkali wash.

An ideal cleaning sequence

Cold water rinse

The post-milking rinse needs to be done immediately after milking or milk collection. It rinses most of the residual milk from the milking system and bulk milk tank.

Hot water alkaline / acid wash

The milking system should be hot washed at least once a day and twice a day during high risk periods (eg when grading, calving). The bulk milk tank should be hot washed after every collection. The purpose of the hot detergent wash is to remove any adhered non-rinsing milk residue. This process should alternate between acid and alkaline in some systematic way to ensure all residues are removed on a routine basis.

Alkaline detergent wash

A hot water alkaline wash should be done at least twice weekly on the milking system and bulk milk tank. The wash water should be recycled for five-seven minutes once water discharging the plant/tank is hot.

Cold water acid wash

The cold water acid wash is normally done at night and hot alkaline washes done after the morning milking.

Acid sanitiser detergent wash

This should always be the final wash through the milking system and bulk milk tank. Acid sanitiser washes can be used hot or cold.

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