7 replies to this topic

[Anca86]

I’ve recently started working as a supplier quality technician at a frozen raw dog food manufacturer, and I’m encountering issues with one of our raw materials. The product arrives as large frozen blocks (40 × 60 × 15 cm). At intake, we carry out a visual inspection for colour changes or off‑odours, check the temperature, then temper the blocks and run them through a metal detector. This step is not a CCP, as our CCP metal detection is performed on the finished product. The detector sensitivity is set to ferrous 6 mm, non‑ferrous 6.5 mm, and stainless steel 8 mm, and the machine was calibrated specifically for this raw material by metal detector engineers.

 

Because the material is beef or lamb tripe, it naturally contains traces of hay and other environmental debris. Recently, we’ve been experiencing a high number of metal detector rejections. When the quality team defrosts and inspects some of these rejected blocks, they occasionally find small wires, grit, or bolus. However, most rejected blocks are not inspected — they are simply returned to the supplier. This has created tension, as we are rejecting product without physical evidence and relying solely on metal detector alarms. The supplier maintains that their tripe is thoroughly cleaned and metal‑detected three times, and they argue that the high iron content of tripe can lead to false positives.

 

I recognise that we need to implement visual verification on our side and provide evidence with each rejection. The difficulty is that the quality team is pushing back, as defrosting every rejected block is time‑consuming and sometimes involves 30 or more blocks in a single run. If no foreign body is found, the rejection is likely a false positive.

I’m looking for ideas on how to reduce false positives with this type of raw material and how to improve our metal rejection process so we can maintain a good working relationship with the supplier. Any suggestions would be greatly appreciated.

 

[SHQuality]

Because the material is beef or lamb tripe, it naturally contains traces of hay and other environmental debris. Recently, we’ve been experiencing a high number of metal detector rejections. When the quality team defrosts and inspects some of these rejected blocks, they occasionally find small wires, grit, or bolus. However, most rejected blocks are not inspected — they are simply returned to the supplier. This has created tension, as we are rejecting product without physical evidence and relying solely on metal detector alarms. The supplier maintains that their tripe is thoroughly cleaned and metal‑detected three times, and they argue that the high iron content of tripe can lead to false positives.

If you sometimes find small wires, your supplier's metal detector either isn't working as intended, or the wires are too small to be detected with the required sensitivity. Are they using the same limits you are? 

 

Since you're also finding grit and bolus, I question their cleaning methods. Have you (or anyone else from your company) seen their procedures or visited for an in-person audit?

[MDaleDDF]

"When the quality team defrosts and inspects some of these rejected blocks, they occasionally find small wires, grit, or bolus"

I guess I'd be curious how often they find foreign material in defrosted blocks.   "Some" and "Occasionally" doesn't sound like a lot, so it would be interesting to see how many.   Although I know that it can be difficult at times to locate whatever caused a kickout as well.

I agree with SHQ that a meeting and visit may be in order, and this may be an issue that can be rectified together with your supplier with some discussion and overview of the processes of each location, and just tell them you don't want to accuse them of anything, but just work together to get to the bottom of it.   It's a pita for both parties no doubt, so working together to figure out root cause would benefit you both, make safer food, and save money.

[Anca86]

If you sometimes find small wires, your supplier's metal detector either isn't working as intended, or the wires are too small to be detected with the required sensitivity. Are they using the same limits you are? 

 

Since you're also finding grit and bolus, I question their cleaning methods. Have you (or anyone else from your company) seen their procedures or visited for an in-person audit? 

The supplier’s detector sensitivity settings differ from ours; they are currently set to 4 mm for ferrous and 5 mm for both non‑ferrous and stainless steel. I am planning a site visit, subject to the supplier’s agreement, so that we can resolve the issue. It will also be useful to understand how they manage false positives, as we currently have no procedure in place for this. Clarifying their approach should help us reduce the quantity of material being unnecessarily rejected, although this may be a little tricky to address

[Anca86]

"When the quality team defrosts and inspects some of these rejected blocks, they occasionally find small wires, grit, or bolus"

I guess I'd be curious how often they find foreign material in defrosted blocks.   "Some" and "Occasionally" doesn't sound like a lot, so it would be interesting to see how many.   Although I know that it can be difficult at times to locate whatever caused a kickout as well.

I agree with SHQ that a meeting and visit may be in order, and this may be an issue that can be rectified together with your supplier with some discussion and overview of the processes of each location, and just tell them you don't want to accuse them of anything, but just work together to get to the bottom of it.   It's a pita for both parties no doubt, so working together to figure out root cause would benefit you both, make safer food, and save money.

I am new to the company, and I understand that the quality team previously carried out a short trial in which frozen blocks of tripe from two different suppliers were defrosted and assessed. The findings were presented to the suppliers. However, no further tripe has been defrosted since, meaning we are now rejecting blocks without any physical evidence, which the suppliers are understandably unhappy about. One of my objectives is to gain a better understanding of each supplier’s process and to reduce unnecessary tripe rejections. I also need to encourage the quality team to resume defrosting and checking for evidence, as well as recording their findings and any false positives.

[SHQuality]

I would first try to quantify how often "some" and "occasionally" was back then. Are there any people who were around at the time you can ask about that? Did your predecessor leave any documentation?

 

I find the situation strange. Your supplier has a lower limit for their metal detection, yet YOU are the one having a system that triggers even though they are supposedly less sensitive.

 

I agree with MDaleDDF. Focus on working together. They argue that the high iron content of tripe can lead to false positives. How are they dealing with that in their own system? Do they have other systems in place to prevent metal contamination earlier in their system than the metal detector? Is there a chance of post detection contamination in their setup?

[Anca86]

I would first try to quantify how often "some" and "occasionally" was back then. Are there any people who were around at the time you can ask about that? Did your predecessor leave any documentation?

 

I find the situation strange. Your supplier has a lower limit for their metal detection, yet YOU are the one having a system that triggers even though they are supposedly less sensitive.

 

I agree with MDaleDDF. Focus on working together. They argue that the high iron content of tripe can lead to false positives. How are they dealing with that in their own system? Do they have other systems in place to prevent metal contamination earlier in their system than the metal detector? Is there a chance of post detection contamination in their setup?

Unfortunately, all I have are photographs of the foreign body that was found. No other information was recorded, such as how many blocks were defrosted or whether each block was contaminated (referring to the rejected one). There’s nothing that gives me a solid background to identify the root cause.

At this stage, the only option is to start from scratch: review and update the existing metal‑detector rejection procedure, gather proper information, and visit the supplier so we can work together on this.

Thank you all for your input — I’m hopeful we’ll get to the bottom of the issue.

[Scampi]

I'm going to play devil's advocate here

 

As tripe would be quite difficult to process, and you've stated you have metal detection as your CCP in the final product...................is your company making a mountain out of a molehill?

 

Get your MD engineer back in, something may have changed on your unit   and Was it calibrated on thawed or frozen material?