Preventing Milk Freezing and Chilling Problems

Cooling milk too hard can be as costly as cooling it too slowly. Frozen or partly frozen milk can cause quality problems, and the causes are usually simple equipment or setup issues you can fix.

Key points

Milk freezes when cooling surfaces are too cold for the volume of milk covering them.
Check for ice, odd thermostat readings and flagged freezing point results.
Make sure the agitator starts at the right time.
Review tank size and pre-cooler changes.
Record changes and fix one thing at a time.

How freezing happens

Milk freezes in a bulk tank when the cooling surface gets colder than the milk can handle, especially when only a small amount of milk covers the cooling area. This often occurs at the start of a milking, when a small volume sits against the cold walls and the agitator has not yet started to mix it.

Ice crystals can form along the cooling surface, and as they melt back into the milk they can carry changes that harm quality. Frozen milk can also show up in your tests as a freezing point result that looks like added water.

Warning signs

Look for ice on the tank walls or small flakes in the milk, especially after the first milking in a batch. Compare the thermostat reading to the actual milk temperature to see if they match. Frequent compressor cycling or very cold readings at the start of a fill are also clues.

Your milk buyer may also tell you that your freezing point result is off or that quality tests have changed. Treat that as a reason to inspect the tank.

Ice or slush on the inside walls
Flakes or crystals in the milk
Thermostat readings that do not match the milk temperature
Compressor running hard on small volumes
Freezing point results flagged by the buyer

Check the agitator and thermostat

The agitator should start as soon as milk touches the sensor or at the point the manufacturer specifies. If it starts late, the first milk sits against the cold surface and can freeze. Test the agitator control and confirm that it runs at the right time.

The thermostat or controller also needs to be set correctly and kept in working order. A faulty sensor can let the compressor run too long. Have your dealer or a technician check the control settings against the manufacturer's directions.

Small volumes and tank size

A tank that is too large for the herd, or a dry period in a small herd, can leave very little milk covering the cooling surface. Ask your dealer whether your tank settings are right for low volumes, and whether any adjustment is possible for your system.

If your herd size changed, review whether your tank still fits.

Pre-coolers and incoming milk temperature

Pre-cooling can change how cold the milk is when it enters the tank, which changes how hard the tank needs to work. Adjustments to a plate cooler or other pre-cooling equipment can lead to milk entering colder than the system was set for. If you recently made a change, check whether tank behavior changed too.

Keep notes of any equipment change and the date, so cause and effect are easier to trace.

Chilling and freezing point tests

Your milk buyer may test freezing point to look for added water. Milk that has been partly frozen or handled in ways that change its makeup can affect that result. If you receive a flagged result, do not assume the cause. Look at water use in the milking system, washing procedures, leaks and tank behavior.

Ask your field representative for the test method and what they expect you to check first.

Common mistakes and next steps

Common mistakes include leaving agitator timing unchecked, ignoring ice on the walls and assuming the thermostat is correct without verifying. Another is making several equipment changes at once without noting them.

Fix one thing at a time, record the change and watch the next few milkings.

Check the agitator timing
Verify the thermostat and sensor
Review tank size and low volume settings
Walk through wash and water use for leaks
Call your dealer or technician for service

When to get help: Call your tank dealer or a refrigeration technician for agitator, thermostat or low-volume problems, and ask your milk buyer's field representative how freezing point results are handled. Follow manufacturer and OSHA guidance for electrical and mechanical work.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

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