Dairy Hygiene
Domestic and international consumers demand high quality dairy products. This requires dairy farmers to supply high-quality raw milk by adhering to food safety requirements, meeting market access requirements, and accepting incentive payments or penalties based on milk quality.
Milk quality
Dairy hygiene includes all activities, processes and equipment associated with cleaning the milking machine, bulk milk vat and other milk harvesting equipment. Maintaining milking plant and dairy hygiene is critical to guaranteeing high levels of milk quality. The aim of these cleaning programs is to remove all milk residues from the plant between milkings and kill (sanitise) any bacteria.
The quality of milk determines its processing capabilities, the quality of its end products, and in turn impacts milk price and dairy farm profitability.
Poor quality milk can result in:
- Longer and more complex processing procedures.
- Inhibition or destruction of starter cultures and subsequent lower product yields
- Increased wastage and costs.
- Reduced flexibility in the types of dairy products it can produce.
- Off-flavours in dairy products.
- Shorter dairy product shelf life.
- Reduced or restricted access to markets.
- Reduced customer demand.
- Negative customer feedback.
Microbial contamination is a major cause of poor-quality milk. One of the main sources of this type of contamination is associated with poor milking machine hygiene due to an ineffective cleaning program and/or cleaning method. Slow and ineffective cooling of the milk provides conditions conducive to bacteria growth, and so can also be a cause of high bacterial numbers and poor-quality milk.
Bacteria in milk
There are many ways to assess the quality of raw milk from the vat before it is processed. Some are subjective measures, such as the smell or look of the milk and others are objectively measured (e.g. fat and protein percentages, temperature, freezing point, bacteria levels).
When it comes to dairy hygiene, the focus is on minimising bacterial contamination of milk, and prompt investigation when high levels of bacteria are detected. There are various types of bacteria that can contaminate milk, and each impacts milk quality differently.
Sources of bacteria may include:
- Inadequately cleaned and disinfected milking equipment.
- Soiled animals (especially teats and udders).
- Inadequate milk cooling.
- Cows with mastitis (rare).
Every Australian milk company has a system outlining how a dairy farm’s supply of milk is assessed. The measures used, and associated thresholds and penalties differ between companies. If bacterial counts are above premium limits, a systematic investigation should be carried out by an experienced staff member or dairy hygiene advisor. In Australia, several different tests are performed on bulk milk samples to quantify bacteria levels. The most commonly used tests are the Total Plate Count (TPC), Bactoscan and Thermoduric counts.
Total Plate Count
The Total Plate Count (TPC) measures the total number live, viable bacteria that grow and form colonies. Bulk milk samples are incubated on agar plates at 30 degrees Celsius for 72 hours. After incubation, the colonies of bacteria are counted visually or electronically. The typical limit for premium quality is less than 20,000 colony forming units per millilitre (cfu/ml).
Bactoscan
The Bactoscan test detects the total number of alive or dead bacteria, by electronically scanning a sample of milk. The typical limit for premium quality is less than 80,000 individual bacterial count per ml (ibc/ml).
Thermoduric
The Thermoduric test measures the total number of bacteria that have survived pasteurisation and are still able to form colonies. Bulk milk samples are first pasteurised at 63.5°C for 30 minutes, then incubated on agar plates at 30°C for 72 hours. After incubation, the colonies of bacteria are counted visually or electronically. The typical limit for premium quality is less than 2,000cfu/ml.