Animal by-product processors: how to carry out a processing test

Find out how to carry out a processing test, which is part of validation for continuous animal by-product processing facilities.

All animal by-product (ABP) processing facilities must be validated by the Animal and Plant Health Agency (APHA) before they can operate. Find out how to get your ABP processor validated.

If you operate a continuous processor, you will need to carry out a processing test as part of validation. A continuous processor is one where you continuously feed material into the cooker (the machine where material is heat-treated), instead of processing material in separate batches.

The test involves sending an insoluble marker (generally manganese dioxide) through the cooker to check that you are meeting the time and temperature requirements of your processing method.

Contact APHA’s laboratory in Newcastle, which is the only laboratory in the UK able to test validation samples:

APHA Newcastle
Whitley Road
Newcastle upon Tyne
NE12 9SE
Telephone 0300 303 8269

The laboratory will send you manganese oxide briquettes and explain how you need to feed them into your cooker. You will also need to agree when you will carry out the test, so the laboratory is prepared to receive samples.

APHA will send a veterinary officer to observe your test.

How to carry out the test

To make sure the test accurately reflects how long material stays in the cooker:

  • add the marker to the material that is being processed as close as possible to the entrance to the cooker
  • take samples of greaves (material exiting the cooker) as soon as possible after material exits the cooker

If, for safety or practical reasons, you have to add the material or take greaves samples at a point that is more than 1 minute before material enters or exits the cooker, factor this into your timings.

The test will last for 3 hours after you add the marker to the processor, unless the APHA veterinary officer has agreed you can end the test earlier (this will only happen if you use a processing method that doesn’t require material to stay in the cooker for a long period of time).

How to take samples during the test

You need to take 500g samples of the greaves exiting the cooker as follows:

  • take the first sample 30 minutes before you add the marker to the cooker
  • then take a sample every 6 minutes until 3 hours after you added the marker to the cooker

You should have a total of 40 samples.

Take the samples with a stainless steel sampling scoop, and wipe the scoop with paper cloths between each sample to ensure none of the marker is carried over between samples.

If you believe you see a fragment of the briquettes of the marker in the greaves, you should try and include it in a sample. If the fragment appears in the greaves between sampling times, you should take an additional sample, and note the time it was taken. You don’t need to do this more than twice if you spot several fragments of the marker.

Where and how to send samples for testing

Place the samples in pots, and label each pot to indicate when the sample was taken.

The first sample you took, 30 minutes before you added the marker to the cooker, should be labelled -30. The next sample should be labelled -24, the next -18 and so on until the final sample that you took (3 hours or 180 minutes after the marker was added), which should be labelled ‘180’.

Secure a lid to each pot with white PVC tape and seal each pot in a polythene bag.

Send the pots to the to the APHA laboratory in Newcastle in a box marked with the words ‘RENDERING VALIDATION ASHING’.

Include a completed laboratory submission form (which the laboratory will provide).

Information you need to record during the test

You also need to record the following data during the test (starting 30 minutes before you add the marker to the cooker, and ending 3 hours after you added it):

  • the temperature at every point in the cooker where you have a thermocouple - take a measurement every 12 minutes
  • the size of particle exiting the cooker - take a measurement every 30 minutes
  • the rate at which you are feeding raw material into the cooker - take a measurement every 12 minutes
  • the level of fat in the cooker or the fat recycling rate if you add fat to your cooker - take a measurement every 18 minutes

How to calculate if you met the time requirements for your processing method

The laboratory results will tell you the concentration of the marker in each of the samples that you sent for testing.

Plot the marker concentration over time, starting at -30 minutes (the first sample) and ending at 180 (the last sample) and draw a trendline between all the points.

Calculate a ‘background level’ of concentration of the marker. This is the average concentration level in the first 5 samples you took (samples ‘-30’ to ‘-6’ that were taken before you added the marker to the cooker).

Draw a straight line across the graph, at a level that is 50% higher than the background level.

The point where your trendline of marker concentration crosses consistently above this straight line is the point when the marker is considered to have exited the cooker. If your trendline spikes above the straight line for 1 sample, but then falls back below, disregard that sample.

Note the time the trendline crosses above the straight line. This is the time taken for material to pass through your cooker. It must be higher than the minimum time required for your processing method, or you won’t pass the test.

You need to supply this graph and your workings to APHA.

How to calculate if you met the temperature requirements for your processing method

Now go back to the temperature measurements you took every 12 minutes from your thermocouples during the test. For each 12 minute data point, chose either:

  • the average of all of the temperatures you recorded at your thermocouples at that time
  • the lowest temperature you recorded at any individual thermocouple at that time

The average temperature will give you a higher temperature reading, making it more likely that you pass the validation test. But if APHA approve your facility, you will be set a minimum temperature to maintain at the exit point of your cooker. This temperature will be higher if you used average temperatures in your validation test.

Plot the average or minimum temperature at every point that you recorded it between time 0 (when the marker was put into the processor) until the time you noted in the previous section (when the marker exited the cooker). Draw a temperature trendline on the graph.

Now draw straight lines across your graph at each of the temperatures specified in your processing method. For example, approved method 2 requires material to be processed at:

  • 120°C for 13 minutes
  • 110°C for 55 minutes
  • 100°C for 95 minutes

You need to draw straight lines at 120°C, 110°C and 100°C.

Note the time the temperature trendline moves above each of those lines, and when it moves back below them.

For each of the specified temperatures, calculate the maximum time the trendline is above the specified temperature. This is the time between when the trendline climbs above the temperature and when it next drops below the temperature. For each of the specified temperatures it must be longer than the minimum required time or you won’t pass the test.

You need to supply this graph and your workings to APHA as part of the validation process.