5 replies to this topic

[Baohan88]

Hello everyone, I would like to ask for advice on how your companies quantitatively assess metal fines collected on magnets during post‑production cleaning.

 

In our process (sweetened condensed milk), during cleaning the magnet trap in the production process, we use water to rinse it and hands to wipe away the metal pieces in the water, then collect any metal fines. Then we filtered it through a 0.5-micron filter paper and see by microscope. Under the microscope, the metal particles we observe are usually in the range of 0.09–0.4 mm and was a lot of it. So far, our QC release method is very basic, if the amount of metal fines is visibly high by the naked eye, we reject the lot.

 

However, I’m looking for a more objective and quantitative method, could you give me some advice:

1. How do you measure the amount of metal fines on magnets?
2. Do you use weight, particle count, or another standardized method?
3. Are there any guidelines, standards, or acceptance criteria that could help me determine when the level of metal dust is considered excessive and requires rejecting the batch?

Any reference, method, or industry practice would be very helpful. Thank you in advance!

 

[GMO]

There are several approaches I'd take to this.

 

Firstly you ask how to measure what is there. I think this could be relatively simple and I wouldn't wash it off. When you wash metal filings, they tend to sink to the bottom of whatever they are rinsed onto and resist further rinsing away. I would take a damp cloth and wipe the magnet, then, if necessary, photograph it.

 

I don't think I can answer on "what is acceptable" because my question which follows is, for milk, why are you getting any? It's an interesting thing that finding metal has become normalised it seems in your process. Why is that?

 

Personally I think this is a bit back to front. You should be defining in your HACCP plan what is and isn't acceptable in terms of foreign matter risk including size. So that should be giving you your release decision, however, what you are detecting is an early warning in your process that something is wrong. It is not normal to find metal pieces on magnets routinely unless for example, you have a root vegetable product where it's conceivable that some fragments would come in with soil, however, even then, you'd question washing processes not just accept it. This needs to be investigated and resolved.

 

For investigation, I'd use a recognised RCA technique like 8 step problem solving or at least fishbone.

 

I'm not sure if you have an equivalent organisation to Campden BRI or RSSL in Vietnam but those are the kinds of places in the UK which could do metal analysis and support an investigation into where it's come from. But there is obviously also stuff you can do on site.

• Inspect machinery for signs of scratches and wear and do this full end to end. Concentrate of course on any areas which are moving.
• Check the finds with a normal magnet, not rare earth to see if it's mild steel or iron (unlikely to be part of your process).
• Check filters are intact and in place and an appropriate gauge for your process.
• Look for any recent maintenance work and see what the process is in general for cleaning up after cutting or grinding.
• Look at cleaning processes. I had an incident once with metal where we found the root cause was how we were washing some removable items, they were bashing each other in a sink so we bought a frame to clean them in.

I'm sure you can think of far more potential root causes. But I'm old enough to have seen enough incidents where a level of failure becomes the norm and accepted. Then you later find there was an issue in your process and you missed the early warning.

[Scampi]

I would suggest you have a process failure             I can think of no reasonable reason short of metal on metal causing "fines" in your particular product/process

 

I would be worrying less about quantifying them (e.g. there should be zero anything above that is a process failure) and more time investigating where they are originating 

[Baohan88]

There are several approaches I'd take to this.

 

Firstly you ask how to measure what is there. I think this could be relatively simple and I wouldn't wash it off. When you wash metal filings, they tend to sink to the bottom of whatever they are rinsed onto and resist further rinsing away. I would take a damp cloth and wipe the magnet, then, if necessary, photograph it.

 

I don't think I can answer on "what is acceptable" because my question which follows is, for milk, why are you getting any? It's an interesting thing that finding metal has become normalised it seems in your process. Why is that?

 

Personally I think this is a bit back to front. You should be defining in your HACCP plan what is and isn't acceptable in terms of foreign matter risk including size. So that should be giving you your release decision, however, what you are detecting is an early warning in your process that something is wrong. It is not normal to find metal pieces on magnets routinely unless for example, you have a root vegetable product where it's conceivable that some fragments would come in with soil, however, even then, you'd question washing processes not just accept it. This needs to be investigated and resolved.

 

For investigation, I'd use a recognised RCA technique like 8 step problem solving or at least fishbone.

 

I'm not sure if you have an equivalent organisation to Campden BRI or RSSL in Vietnam but those are the kinds of places in the UK which could do metal analysis and support an investigation into where it's come from. But there is obviously also stuff you can do on site.

• Inspect machinery for signs of scratches and wear and do this full end to end. Concentrate of course on any areas which are moving.
• Check the finds with a normal magnet, not rare earth to see if it's mild steel or iron (unlikely to be part of your process).
• Check filters are intact and in place and an appropriate gauge for your process.
• Look for any recent maintenance work and see what the process is in general for cleaning up after cutting or grinding.
• Look at cleaning processes. I had an incident once with metal where we found the root cause was how we were washing some removable items, they were bashing each other in a sink so we bought a frame to clean them in.

I'm sure you can think of far more potential root causes. But I'm old enough to have seen enough incidents where a level of failure becomes the norm and accepted. Then you later find there was an issue in your process and you missed the early warning.

 

Thank for your advice. My process includes cleaning → grinding (w/ water) → evaporation (I found metal piece here) → centrifugation → (optional) drying. I installed a magnet after wet almond grinding, followed by grinding tanks to centrifugation, with 200-micron filters after each step to minimize metal contamination.

 

I suspect small metal fragments may come from grinding contact, but inspections of equipment and tanks have not identified any abnormalities or root cause. Upstream, magnets in cleaning and dry grinding material occasionally capture larger metal pieces, though this is rare (checked every 8 hours). And the water flow also has a magnet trap on the pipe but can't catch anything.

 

Since the product must continue to be produced, teams are asking me for an acceptable limit and handling guidance, so I think of quantity of exceptional release. However, I understand this should not be normalized, and the presence of metal should be treated as an early warning requiring further root cause investigation and corrective action. Do you have any suggestions in this kind of situation?

[GMO]

Ah, you didn't say it was almond milk? So there is a grinding process. Makes more sense. I suspect grinding processes will be subject to this but I'd still check set up and Interesting that your centrifugation isn't taking it out. If you have 200 micron filters, how are you getting 0.4mm pieces through? Or are they only 0.4mm in one direction?

 

I'd not assume everything is set up correctly. I'd confirm it.

 

Fact is that a 0.4mm piece of metal isn't going to hurt anyone. An ops leader once said to me "at what point is a foreign body actually fortification?" He was being a dick but there is validity to the fact that iron powders are used as cereal fortification. A little experiment for you: How to extract iron from cereal - BBC Science Focus Magazine

 

But that all said, it should still be minimised.

 

So what I'd do is this:

Ensure that everything is set up as intended. Get the OEM in to look at your grinding process particularly and check the rest of the line. This is your baseline normal performance. What level do you get? None? Or a very very fine powder? Set a limit which is just above this for action but below something reasonable for food safety. The FDA will have you believe up to 7mm is fine but I'm doubtful and that's not in liquids and only for adults. What would make sense is anything which goes above the size of your filtration (i.e. 0.2mm) should prompt stopping the line and investigation IMO. But it's difficult to say as there's something that goes against my gut in accepting contmaination.

 

Anyone with experience in other grinding processes who could wade in. I'm thinking milling?

[PQEdwards]

The processes that I assess involve ingredients that are mildly abrasive and involve milling processes, so the presence of fine metal particulates is considered technically unavoidable. Control is provided by magnets throughout the processes and montoring of the size and quantity of debris collected. Our approach has been to determine what has been historically normal (and accepted by customers) and establish alarm limits based on this. Also the presence of any large particle is not acceptable. Any deviation from these limits indicate a process issue that needs immediate investigation and isolation of the product.