You check total plate count and coliforms by sending representative, sealed samples to an accredited food microbiology lab. Ask for results by named methods, such as the relevant ISO methods, and compare them against limits written in your spec.
The test itself is routine. Most problems come from poor sampling, unclear limits or relying only on the supplier's own certificate.
What the tests tell you
- Total plate count (TPC), also called aerobic plate count or total viable count: a broad measure of how many bacteria the product carries.
- Coliforms: a group of bacteria that indicate general hygiene during processing and handling.
- E. coli: a more specific sign of faecal contamination.
- Yeast and mould: relevant to storage and moisture control.
- Pathogens such as Salmonella: tested separately, usually as absent or present in a set sample weight.
Why onion counts can be high
Onion grows in soil, and belt drying uses air temperatures that dry the product without fully sterilising it. Untreated dehydrated onion can therefore carry fairly high counts. Many buyers in food manufacturing ask for a treated, lower count product, which is covered in whether dehydrated onion is steam sterilised.
Sampling properly
- Take samples from several cartons or bags across the lot, not from one.
- Use clean, sterile tools and bags, and seal and label them on the spot.
- Keep a duplicate sealed sample in case results are disputed.
- Record the lot number, date and cartons sampled.
- Send to the lab promptly, with the methods and limits stated on the request.
Choosing the lab and methods
In India, use a lab accredited by NABL for the specific tests you need, not just accredited in general. Check the lab's scope. Common reference methods include ISO 4833-1 for colony count and ISO methods for coliforms and E. coli. Some US buyers prefer FDA Bacteriological Analytical Manual methods. Name the method in your contract so results are comparable.
Results are reported in colony forming units per gram (cfu/g). Read the report carefully: units, method, sample date and the lab's accreditation mark. Our guide to reading a lab certificate explains what to look for.
Setting limits
There is no single limit for all markets. Your limits should come from your own customers, your food safety plan and the product's use. A seasoning eaten without further cooking needs stricter limits than onion that will be boiled in a soup.
Write separate limits for TPC, coliforms, E. coli, yeast and mould, and Salmonella. Then decide whether each lot is tested before shipment, on arrival or both. The specification guide for dehydrated onion powder shows how these fit with the physical limits.
How we help
We draw sealed samples from the packed lot ourselves and send them to an NABL-accredited lab with your methods and limits. You receive the original report, not a summary. To set this up for your next order, ask for a free sourcing review.