How to investigate a food customer complaint: from the first call to the root cause

A consumer phones to say she found a piece of blue plastic in a biscuit. A retailer emails about a “funny smell” on three packs of polony. On many sites the complaint is logged, a voucher goes out and the file is closed, and three months later the same plastic turns up again. A food complaint investigation procedure that works treats every complaint as evidence and follows it until the real cause is found and fixed.

Classify first: safety, legality or quality

The first decision sets the pace of everything else. Classify each complaint as soon as it arrives:

Class	Examples	First response
Food safety	Glass, metal, hard plastic, suspected illness, undeclared allergen, mould in a product where it should not grow, chemical taste	Escalate to the QA manager the same day; check whether other product is affected
Legality	Missing or wrong allergen information, wrong date code, underweight packs, wrong label	Escalate the same day; check the whole batch and the labels in stock
Quality	Taste, texture, colour, broken product, poor seal with no safety impact	Investigate within your normal target time

Set your own response times for each class and write them into the procedure. If there is any doubt between classes, treat it as the more serious one until the evidence says otherwise. An undeclared allergen is a legality issue and a food safety issue at the same time.

Gathering the evidence: sample, batch and traceability

The quality of the investigation depends on what you collect in the first conversation. Train whoever takes complaints to record:

• the product name, pack size, batch or lot code, best before date and any time code;
• where and when it was bought and how it was stored afterwards;
• exactly what was found, where in the product and how much was eaten;
• any illness, with symptoms and timing, without speculating about the cause;
• photographs, and arrangements to collect the sample and the packaging.

Get the physical sample back wherever possible, and keep it labelled and secure. Then pull the internal evidence for that batch: production records, CCP and metal detector checks, sieve and magnet inspections, cleaning records, maintenance and engineering work orders, raw material lots used, retained samples and any other complaints on the same batch or date. Good traceability turns a vague complaint into a defined window of production. The Traceability, Withdrawal and Recall Risk Assessment Template (RA20) helps you test that your system can deliver that information fast.

Investigating on site: test each possible cause

List every possible cause, then test each one against the evidence. For a foreign body, examine the item closely: what material, what colour, what shape, any wear marks. Then go to the line and look for where it could have come from. For a biscuit with blue plastic, that means checking every blue plastic item in the area: scrapers, scoops, ingredient bags, gloves, detectable tape and equipment parts.

Rule possible causes out with evidence, not opinion. If the metal detector was checked and passed every hour, a metal complaint is less likely to be from production, but it is not proof. If the plastic matches the colour and thickness of a worn scraper blade, that is a strong lead. Also consider causes outside your site: damage in distribution, tampering, or contamination after the pack was opened.

For complaints about suspected illness, be careful. Bacteria such as Salmonella, Staphylococcus aureus or Bacillus cereus can cause illness, but the food eaten last is not always the cause. Onset times differ by organism, from a few hours for the toxins of Staphylococcus aureus and Bacillus cereus to a day or more for Salmonella, so ask what else the person ate in the days before. Check retained samples, batch microbiology and process records, and work with the consumer’s medical information where it is offered.

Getting to root cause with 5 Whys and a fishbone

A fishbone diagram helps the team think widely. Draw the problem at the head and list possible causes under headings such as people, methods, machines, materials, measurement and environment. Then use 5 Whys on the most likely branch to dig down to the cause you can fix.

A worked example from a biscuit factory in KwaZulu-Natal

A biscuit manufacturer in KwaZulu-Natal received two complaints of blue plastic in one month. The fragment matched the blade of a hand scraper used on the dough sheeter. The 5 Whys ran like this:

1. Why was there plastic in the biscuit? A piece of scraper blade broke off into the dough.
2. Why did it break off? The blade edge was worn and chipped.
3. Why was a worn blade in use? Nobody checked scrapers for wear.
4. Why was there no check? Scrapers were not on the hard plastics register.
5. Why were they not on the register? The register only covered fixed items, not hand tools.

The root cause was a gap in the register, not a careless operator. The site added all hand tools to the register, introduced a start of shift check, and switched to metal detectable scrapers. They verified the fix by tracking foreign matter complaints over the following six months. Notice that “human error” never appears as the answer. If your investigation ends at “operator was careless”, keep asking why.

Our Conducting a Root Cause Analysis course trains your team to use these tools properly, so investigations reach causes you can actually fix.

Responding to the customer and closing the file

Acknowledge the complaint quickly, thank the person and tell them what will happen next. Do not admit or deny cause before the investigation is done. When you reply with findings, be clear and honest about what you found and what you have changed. Retailers will expect a formal report, often within a time they set.

Close the file only when:

• the root cause is identified and recorded;
• corrective actions are complete;
• someone has verified that the actions worked;
• the customer has had a response.

An open corrective action with a closed complaint is one of the most common findings we raise on internal food safety audits.

Trending complaints per million units

Raw complaint numbers rise and fall with sales, so trend them as a rate. Divide the number of complaints by the units sold and multiply by one million. A site that received 18 complaints on 4.5 million units in a quarter has a rate of 4 complaints per million units.

Then split the rate by category, product, line and month. A Pareto chart of categories usually shows two or three causes making up most of the complaints, and those are the ones to target. Report the trend at food safety team meetings and management review, and set reduction targets for the biggest categories. Rising trends should feed straight into your internal audit schedule.

When a complaint becomes a withdrawal or recall

Most complaints are single events. Some are the first sign of a wider problem. Ask: is there evidence that other units in the same batch are affected, and could they harm consumers or break the law? Examples include an undeclared allergen caused by a wrong label, a pathogen such as Listeria monocytogenes found in retained samples, or glass from a breakage that was not picked up.

A withdrawal removes product from the distribution chain before it reaches consumers. A recall brings back product that consumers already have. Your procedure should say who decides, how quickly, and who must be told, including customers, your certification body as your scheme requires, and the relevant authorities. In South Africa, the Consumer Protection Act and the National Consumer Commission’s recall guidelines set out how a product recall is reported. Practise it with a mock recall so the first real one is not the first time the team sees the procedure. If your system needs strengthening, our HACCP and GMP implementation consulting can help.

What to do this week

• Check that your complaint form captures batch code, date code and sample details.
• Add safety, legality and quality classes with response times to your procedure.
• Pick your last three closed complaints and check each has a verified root cause.
• Calculate your complaints per million units for the last quarter by category.
• Confirm the criteria and decision makers for a withdrawal or recall.