Milk is an excellent growth medium for bacteria and unless the machine washing routine is correct you can increase the rate of bacteria growth.Bacteria live in soil, silage, faeces, skin, etc, and with inadequate cleaning, deposits build up on milking machine surfaces. The best farmers achieve thermoduric counts less than 200/ml and total bacteria counts (TBC) less than 20 on a regular basis. Results greater than both these figures often indicate the wash routine is inadequate.