High fat dairy products, such as butter, can be contaminated with a residue called Trichloromethane (TCM). Formation of TCM can occur during the milking process if chlorine-containing detergents are used to clean the milking machine and bulk tank. Residues of these detergents can combine with fat in the milk to form TCM and this can be concentrated in products such as cream and butter. The current limit in milk is <0.00124mg/kg; this is easily achieved when chlorine-free detergents are used for milking plant cleaning, which is now required by most milk processors.

The key points to achieving a low TCM score are:

• use chlorine-free products to clean milking machine equipment
• do not stock pile chemicals
• store chemicals correctly out of direct sunlight
• use adequate rinse levels for all rinses (14l/unit)
• ensure adequate drainage of the milking system between milkings
• ensure detergents are in date
• read the label
• ensure automatic wash systems are calibrated correctly
• avoid teat disinfectants that contain chlorine dioxide/chloride or iodine

Peracetic acid should be used as a replacement for chlorine for disinfection of wells or to sterilise a milking plant or bulk milk tank before the next milking if water quality is an issue on farms. It can also be used to disinfect clusters between individual cow milkings if transfer of mastitis-causing bacteria is an issue on farm.