Trouble-shooting high LPCs


By Noelia Silva-del-Rio, UC Davis Dairy Specialist

Carol Collar, UCD Kings County Dairy Advisor

High Laboratory Pasteurization Count (LPC) values indicate bacteria resistant to high temperature (thermoduric) are present in bulk tank milk. These bacteria survive pasteurization and decrease milk shelf life.

Thermoduric bacteria are found in soil and manure. They reach the milk through dirty udders and can grow rapidly in the milking equipment either during long milking shifts or when the milking equipment is not properly cleaned.

If you have high LPC, it may be worth your time to check the following areas:

Thermoduric bacteria grow exponentially on in-line filters if milkings last more than 4 hours. Change out filters as appropriate if your milking time exceeds this.

1) Temperature, chemical concentration, and duration of the wash cycles.

Follow the chemical label recommendations and check:

a) Water temperature at the wash sink (use a thermometer). 

Remember, temperatures above or below the recommended range may have a negative effect on your wash system.

b) Alkalinity or acidity of the washing solutions (use pH strips: 1-14 pH).

Remember, the concentration of cleaning chemicals should be adjusted according to water hardness. Make sure your water is not contaminated with bacteria.

c) Timing of the different cleaning cycles (use a stop-watch). Your equipment manufacturer will provide the calculated water volume and length of your washing cycles. Recommended guidelines:

Pre-wash Rinse – Temperature: 100-120° F.; Time: Until the discharge is clear.

Detergent Wash – Temperature 140-165° F (never below 120° F); pH 11-13; Time: 10 minutes.

Acid Rinse – Temperature 90-110° F (some chemicals cold); pH: <4.

2) Sanitation and wear of liners, milk hoses, jetters and gaskets.

Replace those as often as recommended. Check the pieces that you are replacing for wear and sanitation. If you see cracks or wrinkles you need to replace those sooner.

Remember: 1) Cracks can harbor bacteria; and 2) high concentration of cleaning chemicals increases wear of rubber parts.

Use pH strips to check the alkalinity or acidity of the washing solutions.

3) Drainage.

The pipeline should be properly sloped with the appropriate secondary drains. Check for pipes, hoses, fittings and equipment that do not drain when the system is shut off.

4) Duration of milking shifts.

Thermoduric bacteria grow exponentially on in-line filters if milkings last more than 4 hours. Change out filters as appropriate if your milking time exceeds this.

5) Air injectors.

Air injectors should be placed properly for a good “scrubbing” action and they should be kept clean. Signs related to air injector problems include:

1) The water level in the receiver does not change during cleaning.

2) The milk pump never shuts off.

3) The ball valve in the sanitary trap shuts off the vacuum.

4) There are large volumes of water in the distribution tank.

5) Air is entering the system at the wash tank.

Remember: Air can carry bacteria from the environment to the milk equipment surfaces. It is important to maintain the cleanliness of your air lines and the sanitary trap.

6) Other problems. 

1) Pipe bends and pipe dead ends that are difficult to clean.

2) Small components that are tough to reach (milk meters, take off sensors, etc.)

3) Milk level in the receiver can raise up on occasion and leave a milk film. Hours may pass before it is cleaned.

• To contact Noelia Silva-del-Rio, e-mail her at To contact Carol Collar, e-mail her at